diff --git a/benchmarks/BM_ADSR.cpp b/benchmarks/BM_ADSR.cpp
index 0977c149..762c4804 100644
--- a/benchmarks/BM_ADSR.cpp
+++ b/benchmarks/BM_ADSR.cpp
@@ -35,7 +35,7 @@ public:
     }
 
     sfz::MidiState midiState;
-    sfz::Region region{0, midiState};
+    sfz::Region region{0};
     sfz::ADSREnvelope envelope;
     std::vector<float> output;
 };
diff --git a/common.mk b/common.mk
index abe2b26c..21ca24b3 100644
--- a/common.mk
+++ b/common.mk
@@ -89,6 +89,7 @@ SFIZZ_SOURCES = \
 	src/sfizz/FlexEGDescription.cpp \
 	src/sfizz/FlexEnvelope.cpp \
 	src/sfizz/Interpolators.cpp \
+	src/sfizz/Layer.cpp \
 	src/sfizz/Logger.cpp \
 	src/sfizz/LFO.cpp \
 	src/sfizz/LFODescription.cpp \
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 64d616aa..1538b4cc 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -75,6 +75,7 @@ set(SFIZZ_HEADERS
     sfizz/HistoricalBuffer.h
     sfizz/Interpolators.h
     sfizz/Interpolators.hpp
+    sfizz/Layer.h
     sfizz/Logger.h
     sfizz/LFO.h
     sfizz/LFOCommon.h
@@ -157,6 +158,7 @@ set(SFIZZ_SOURCES
     sfizz/SynthMessaging.cpp
     sfizz/WindowedSinc.cpp
     sfizz/Interpolators.cpp
+    sfizz/Layer.cpp
     sfizz/modulations/ModId.cpp
     sfizz/modulations/ModKey.cpp
     sfizz/modulations/ModKeyHash.cpp
diff --git a/src/sfizz/Layer.cpp b/src/sfizz/Layer.cpp
new file mode 100644
index 00000000..3f3b823f
--- /dev/null
+++ b/src/sfizz/Layer.cpp
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#include "Layer.h"
+#include "Region.h"
+#include "utility/Debug.h"
+#include "utility/SwapAndPop.h"
+#include <absl/algorithm/container.h>
+
+namespace sfz {
+
+Layer::Layer(std::unique_ptr<Region> region, const MidiState& midiState)
+    : Layer(region.get(), midiState)
+{
+    regionOwned_ = true;
+    region.release();
+}
+
+Layer::Layer(Region* region, const MidiState& midiState)
+    : region_(region), regionOwned_(false), midiState_(midiState)
+{
+    initializeActivations();
+}
+
+Layer::~Layer()
+{
+    if (regionOwned_)
+        delete region_;
+}
+
+void Layer::initializeActivations()
+{
+    const Region& region = *region_;
+
+    keySwitched_ = !region.usesKeySwitches;
+    previousKeySwitched_ = !region.usesPreviousKeySwitches;
+    sequenceSwitched_ = !region.usesSequenceSwitches;
+    pitchSwitched_ = true;
+    bpmSwitched_ = true;
+    aftertouchSwitched_ = true;
+    ccSwitched_.set();
+}
+
+bool Layer::isSwitchedOn() const noexcept
+{
+    return keySwitched_ && previousKeySwitched_ && sequenceSwitched_ && pitchSwitched_ && bpmSwitched_ && aftertouchSwitched_ && ccSwitched_.all();
+}
+
+bool Layer::registerNoteOn(int noteNumber, float velocity, float randValue) noexcept
+{
+    ASSERT(velocity >= 0.0f && velocity <= 1.0f);
+
+    const Region& region = *region_;
+
+    const bool keyOk = region.keyRange.containsWithEnd(noteNumber);
+    if (keyOk) {
+        // Sequence activation
+        sequenceSwitched_ =
+            ((sequenceCounter_++ % region.sequenceLength) == region.sequencePosition - 1);
+    }
+
+    if (!isSwitchedOn())
+        return false;
+
+    if (!region.triggerOnNote)
+        return false;
+
+    if (region.velocityOverride == VelocityOverride::previous)
+        velocity = midiState_.getLastVelocity();
+
+    const bool velOk = region.velocityRange.containsWithEnd(velocity);
+    const bool randOk = region.randRange.contains(randValue) || (randValue >= 1.0f && region.randRange.isValid() && region.randRange.getEnd() >= 1.0f);
+    const bool firstLegatoNote = (region.trigger == Trigger::first && midiState_.getActiveNotes() == 1);
+    const bool attackTrigger = (region.trigger == Trigger::attack);
+    const bool notFirstLegatoNote = (region.trigger == Trigger::legato && midiState_.getActiveNotes() > 1);
+
+    return keyOk && velOk && randOk && (attackTrigger || firstLegatoNote || notFirstLegatoNote);
+}
+
+bool Layer::registerNoteOff(int noteNumber, float velocity, float randValue) noexcept
+{
+    ASSERT(velocity >= 0.0f && velocity <= 1.0f);
+
+    const Region& region = *region_;
+
+    if (!isSwitchedOn())
+        return false;
+
+    if (!region.triggerOnNote)
+        return false;
+
+    // Prerequisites
+
+    const bool keyOk = region.keyRange.containsWithEnd(noteNumber);
+    const bool velOk = region.velocityRange.containsWithEnd(velocity);
+    const bool randOk = region.randRange.contains(randValue) || (randValue >= 1.0f && region.randRange.isValid() && region.randRange.getEnd() >= 1.0f);
+
+    if (!(velOk && keyOk && randOk))
+        return false;
+
+    // Release logic
+
+    if (region.trigger == Trigger::release_key)
+        return true;
+
+    if (region.trigger == Trigger::release) {
+        const bool sostenutoed = isNoteSostenutoed(noteNumber);
+
+        if (sostenutoed && !sostenutoPressed_) {
+            removeFromSostenutoReleases(noteNumber);
+            if (sustainPressed_)
+                delaySustainRelease(noteNumber, midiState_.getNoteVelocity(noteNumber));
+        }
+
+        if (!sostenutoPressed_ || !sostenutoed) {
+            if (sustainPressed_)
+                delaySustainRelease(noteNumber, midiState_.getNoteVelocity(noteNumber));
+            else
+                return true;
+        }
+    }
+
+    return false;
+}
+
+bool Layer::registerCC(int ccNumber, float ccValue) noexcept
+{
+    ASSERT(ccValue >= 0.0f && ccValue <= 1.0f);
+
+    const Region& region = *region_;
+
+    if (ccNumber == region.sustainCC)
+        sustainPressed_ = region.checkSustain && ccValue >= region.sustainThreshold;
+
+    if (ccNumber == region.sostenutoCC) {
+        const bool newState = region.checkSostenuto && ccValue >= region.sostenutoThreshold;
+        if (!sostenutoPressed_ && newState)
+            storeSostenutoNotes();
+
+        if (!newState && sostenutoPressed_)
+            delayedSostenutoReleases_.clear();
+
+        sostenutoPressed_ = newState;
+    }
+
+    if (region.ccConditions.getWithDefault(ccNumber).containsWithEnd(ccValue))
+        ccSwitched_.set(ccNumber, true);
+    else
+        ccSwitched_.set(ccNumber, false);
+
+    if (!isSwitchedOn())
+        return false;
+
+    if (!region.triggerOnCC)
+        return false;
+
+    if (auto triggerRange = region.ccTriggers.get(ccNumber)) {
+        if (triggerRange->containsWithEnd(ccValue))
+            return true;
+    }
+
+    return false;
+}
+
+void Layer::registerPitchWheel(float pitch) noexcept
+{
+    const Region& region = *region_;
+    if (region.bendRange.containsWithEnd(pitch))
+        pitchSwitched_ = true;
+    else
+        pitchSwitched_ = false;
+}
+
+void Layer::registerAftertouch(float aftertouch) noexcept
+{
+    const Region& region = *region_;
+    if (region.aftertouchRange.containsWithEnd(aftertouch))
+        aftertouchSwitched_ = true;
+    else
+        aftertouchSwitched_ = false;
+}
+
+void Layer::registerTempo(float secondsPerQuarter) noexcept
+{
+    const Region& region = *region_;
+    const float bpm = 60.0f / secondsPerQuarter;
+    if (region.bpmRange.containsWithEnd(bpm))
+        bpmSwitched_ = true;
+    else
+        bpmSwitched_ = false;
+}
+
+void Layer::delaySustainRelease(int noteNumber, float velocity) noexcept
+{
+    if (delayedSustainReleases_.size() == delayedSustainReleases_.capacity())
+        return;
+
+    delayedSustainReleases_.emplace_back(noteNumber, velocity);
+}
+
+void Layer::delaySostenutoRelease(int noteNumber, float velocity) noexcept
+{
+    if (delayedSostenutoReleases_.size() == delayedSostenutoReleases_.capacity())
+        return;
+
+    delayedSostenutoReleases_.emplace_back(noteNumber, velocity);
+}
+
+void Layer::removeFromSostenutoReleases(int noteNumber) noexcept
+{
+    swapAndPopFirst(delayedSostenutoReleases_, [=](const std::pair<int, float>& p) {
+        return p.first == noteNumber;
+    });
+}
+
+void Layer::storeSostenutoNotes() noexcept
+{
+    ASSERT(delayedSostenutoReleases_.empty());
+    const Region& region = *region_;
+    for (int note = region.keyRange.getStart(); note <= region.keyRange.getEnd(); ++note) {
+        if (midiState_.isNotePressed(note))
+            delaySostenutoRelease(note, midiState_.getNoteVelocity(note));
+    }
+}
+
+
+bool Layer::isNoteSustained(int noteNumber) const noexcept
+{
+    return absl::c_find_if(delayedSustainReleases_, [=](const std::pair<int, float>& p) {
+        return p.first == noteNumber;
+    }) != delayedSustainReleases_.end();
+}
+
+bool Layer::isNoteSostenutoed(int noteNumber) const noexcept
+{
+    return absl::c_find_if(delayedSostenutoReleases_, [=](const std::pair<int, float>& p) {
+        return p.first == noteNumber;
+    }) != delayedSostenutoReleases_.end();
+}
+
+} // namespace sfz
diff --git a/src/sfizz/Layer.h b/src/sfizz/Layer.h
new file mode 100644
index 00000000..619d7d5a
--- /dev/null
+++ b/src/sfizz/Layer.h
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include "Config.h"
+#include "utility/NumericId.h"
+#include "utility/LeakDetector.h"
+#include <utility>
+#include <string>
+#include <vector>
+#include <bitset>
+#include <memory>
+
+namespace sfz {
+struct Region;
+class MidiState;
+
+struct Layer {
+public:
+    Layer(std::unique_ptr<Region> region, const MidiState& midiState);
+    Layer(Region* region, const MidiState& midiState);
+    ~Layer();
+
+    Layer(const Layer&) = delete;
+    Layer(Layer&&) = delete;
+    Layer& operator=(const Layer&) = delete;
+    Layer& operator=(Layer&&) = delete;
+
+    /**
+     * @brief Get the region that this layer operates on.
+     */
+    const Region& getRegion() const noexcept { return *region_; }
+    /**
+     * @brief Get the region that this layer operates on.
+     */
+    Region& getRegion() noexcept { return *region_; }
+
+    /**
+     * @brief Reset the activations to their initial states.
+     */
+    void initializeActivations();
+
+    /**
+     * @brief Given the current midi state, is the region switched on?
+     *
+     * @return true
+     * @return false
+     */
+    bool isSwitchedOn() const noexcept;
+    /**
+     * @brief Register a new note on event. The region may be switched on or off using keys so
+     * this function updates the keyswitches state.
+     *
+     * @param noteNumber
+     * @param velocity
+     * @param randValue a random value between 0 and 1 used to randomize a bit the region activations
+     *                  and vary the samples
+     * @return true if the region should trigger on this event.
+     * @return false
+     */
+    bool registerNoteOn(int noteNumber, float velocity, float randValue) noexcept;
+    /**
+     * @brief Register a new note off event. The region may be switched on or off using keys so
+     * this function updates the keyswitches state.
+     *
+     * @param noteNumber
+     * @param velocity
+     * @param randValue a random value between 0 and 1 used to randomize a bit the region activations
+     *                  and vary the samples
+     * @return true if the region should trigger on this event.
+     * @return false
+     */
+    bool registerNoteOff(int noteNumber, float velocity, float randValue) noexcept;
+    /**
+     * @brief Register a new CC event. The region may be switched on or off using CCs so
+     * this function checks if it indeeds need to activate or not.
+     *
+     * @param ccNumber
+     * @param ccValue
+     * @return true if the region should trigger on this event
+     * @return false
+     */
+    bool registerCC(int ccNumber, float ccValue) noexcept;
+    /**
+     * @brief Register a new pitch wheel event.
+     *
+     * @param pitch
+     */
+    void registerPitchWheel(float pitch) noexcept;
+    /**
+     * @brief Register a new aftertouch event.
+     *
+     * @param aftertouch
+     */
+    void registerAftertouch(float aftertouch) noexcept;
+    /**
+     * @brief Register tempo
+     *
+     * @param secondsPerQuarter
+     */
+    void registerTempo(float secondsPerQuarter) noexcept;
+
+    Region* const region_ {};
+    bool regionOwned_ = false;
+
+    // Started notes
+    bool sustainPressed_ { false };
+    bool sostenutoPressed_ { false };
+    std::vector<std::pair<int, float>> delayedSustainReleases_;
+    std::vector<std::pair<int, float>> delayedSostenutoReleases_;
+    void delaySustainRelease(int noteNumber, float velocity) noexcept;
+    void delaySostenutoRelease(int noteNumber, float velocity) noexcept;
+    void storeSostenutoNotes() noexcept;
+    void removeFromSostenutoReleases(int noteNumber) noexcept;
+    bool isNoteSustained(int noteNumber) const noexcept;
+    bool isNoteSostenutoed(int noteNumber) const noexcept;
+
+    const MidiState& midiState_;
+    bool keySwitched_ {};
+    bool previousKeySwitched_ {};
+    bool sequenceSwitched_ {};
+    bool pitchSwitched_ {};
+    bool bpmSwitched_ {};
+    bool aftertouchSwitched_ {};
+    std::bitset<config::numCCs> ccSwitched_;
+
+    int sequenceCounter_ { 0 };
+
+    LEAK_DETECTOR(Layer);
+};
+
+} // namespace sfz
diff --git a/src/sfizz/Region.cpp b/src/sfizz/Region.cpp
index 90f4b046..cfc84355 100644
--- a/src/sfizz/Region.cpp
+++ b/src/sfizz/Region.cpp
@@ -6,6 +6,7 @@
 
 #include "Region.h"
 #include "Opcode.h"
+#include "MidiState.h"
 #include "MathHelpers.h"
 #include "utility/SwapAndPop.h"
 #include "utility/StringViewHelpers.h"
@@ -35,11 +36,9 @@ bool extendIfNecessary(std::vector<T>& vec, unsigned size, unsigned defaultCapac
     return true;
 }
 
-sfz::Region::Region(int regionNumber, const MidiState& midiState, absl::string_view defaultPath)
-: id{regionNumber}, midiState(midiState), defaultPath(defaultPath)
+sfz::Region::Region(int regionNumber, absl::string_view defaultPath)
+: id{regionNumber}, defaultPath(defaultPath)
 {
-    ccSwitched.set();
-
     gainToEffect.reserve(5); // sufficient room for main and fx1-4
     gainToEffect.push_back(1.0); // contribute 100% into the main bus
 
@@ -260,7 +259,7 @@ bool sfz::Region::parseOpcode(const Opcode& rawOpcode)
     case hash("sw_last"):
         if (!lastKeyswitchRange) {
             lastKeyswitch = opcode.readOptional(Default::key);
-            keySwitched = !lastKeyswitch.has_value();
+            usesKeySwitches = lastKeyswitch.has_value();
         }
         break;
     case hash("sw_lolast"):
@@ -271,7 +270,7 @@ bool sfz::Region::parseOpcode(const Opcode& rawOpcode)
             else
                 lastKeyswitchRange->setStart(value);
 
-            keySwitched = false;
+            usesKeySwitches = true;
             lastKeyswitch = absl::nullopt;
         }
         break;
@@ -283,7 +282,7 @@ bool sfz::Region::parseOpcode(const Opcode& rawOpcode)
             else
                 lastKeyswitchRange->setEnd(value);
 
-            keySwitched = false;
+            usesKeySwitches = true;
             lastKeyswitch = absl::nullopt;
         }
         break;
@@ -292,14 +291,14 @@ bool sfz::Region::parseOpcode(const Opcode& rawOpcode)
         break;
     case hash("sw_down"):
         downKeyswitch = opcode.readOptional(Default::key);
-        keySwitched = !downKeyswitch.has_value();
+        usesKeySwitches = downKeyswitch.has_value();
         break;
     case hash("sw_up"):
         upKeyswitch = opcode.readOptional(Default::key);
         break;
     case hash("sw_previous"):
         previousKeyswitch = opcode.readOptional(Default::key);
-        previousKeySwitched = !previousKeyswitch.has_value();
+        usesPreviousKeySwitches = previousKeyswitch.has_value();
         break;
     case hash("sw_vel"):
         velocityOverride =
@@ -348,7 +347,7 @@ bool sfz::Region::parseOpcode(const Opcode& rawOpcode)
         break;
     case hash("seq_position"):
         sequencePosition = opcode.read(Default::sequence);
-        sequenceSwitched = false;
+        usesSequenceSwitches = true;
         break;
     // Region logic: triggers
     case hash("trigger"):
@@ -1499,191 +1498,6 @@ bool sfz::Region::processGenericCc(const Opcode& opcode, OpcodeSpec<float> spec,
     return true;
 }
 
-bool sfz::Region::isSwitchedOn() const noexcept
-{
-    return keySwitched && previousKeySwitched && sequenceSwitched && pitchSwitched && bpmSwitched && aftertouchSwitched && ccSwitched.all();
-}
-
-void sfz::Region::delaySustainRelease(int noteNumber, float velocity) noexcept
-{
-    if (delayedSustainReleases.size() == delayedSustainReleases.capacity())
-        return;
-
-    delayedSustainReleases.emplace_back(noteNumber, velocity);
-}
-
-void sfz::Region::delaySostenutoRelease(int noteNumber, float velocity) noexcept
-{
-    if (delayedSostenutoReleases.size() == delayedSostenutoReleases.capacity())
-        return;
-
-    delayedSostenutoReleases.emplace_back(noteNumber, velocity);
-}
-
-void sfz::Region::removeFromSostenutoReleases(int noteNumber) noexcept
-{
-    swapAndPopFirst(delayedSostenutoReleases, [=](const std::pair<int, float>& p) {
-        return p.first == noteNumber;
-    });
-}
-
-void sfz::Region::storeSostenutoNotes() noexcept
-{
-    ASSERT(delayedSostenutoReleases.empty());
-    for (int note = keyRange.getStart(); note <= keyRange.getEnd(); ++note) {
-        if (midiState.isNotePressed(note))
-            delaySostenutoRelease(note, midiState.getNoteVelocity(note));
-    }
-}
-
-
-bool sfz::Region::isNoteSustained(int noteNumber) const noexcept
-{
-    return absl::c_find_if(delayedSustainReleases, [=](const std::pair<int, float>& p) {
-        return p.first == noteNumber;
-    }) != delayedSustainReleases.end();
-}
-
-bool sfz::Region::isNoteSostenutoed(int noteNumber) const noexcept
-{
-    return absl::c_find_if(delayedSostenutoReleases, [=](const std::pair<int, float>& p) {
-        return p.first == noteNumber;
-    }) != delayedSostenutoReleases.end();
-}
-
-bool sfz::Region::registerNoteOn(int noteNumber, float velocity, float randValue) noexcept
-{
-    ASSERT(velocity >= 0.0f && velocity <= 1.0f);
-
-    const bool keyOk = keyRange.containsWithEnd(noteNumber);
-    if (keyOk) {
-        // Sequence activation
-        sequenceSwitched =
-            ((sequenceCounter++ % sequenceLength) == sequencePosition - 1);
-    }
-
-    if (!isSwitchedOn())
-        return false;
-
-    if (!triggerOnNote)
-        return false;
-
-    if (velocityOverride == VelocityOverride::previous)
-        velocity = midiState.getLastVelocity();
-
-    const bool velOk = velocityRange.containsWithEnd(velocity);
-    const bool randOk = randRange.contains(randValue) || (randValue >= 1.0f && randRange.isValid() && randRange.getEnd() >= 1.0f);
-    const bool firstLegatoNote = (trigger == Trigger::first && midiState.getActiveNotes() == 1);
-    const bool attackTrigger = (trigger == Trigger::attack);
-    const bool notFirstLegatoNote = (trigger == Trigger::legato && midiState.getActiveNotes() > 1);
-
-    return keyOk && velOk && randOk && (attackTrigger || firstLegatoNote || notFirstLegatoNote);
-}
-
-bool sfz::Region::registerNoteOff(int noteNumber, float velocity, float randValue) noexcept
-{
-    ASSERT(velocity >= 0.0f && velocity <= 1.0f);
-
-    if (!isSwitchedOn())
-        return false;
-
-    if (!triggerOnNote)
-        return false;
-
-    // Prerequisites
-
-    const bool keyOk = keyRange.containsWithEnd(noteNumber);
-    const bool velOk = velocityRange.containsWithEnd(velocity);
-    const bool randOk = randRange.contains(randValue) || (randValue >= 1.0f && randRange.isValid() && randRange.getEnd() >= 1.0f);
-
-    if (!(velOk && keyOk && randOk))
-        return false;
-
-    // Release logic
-
-    if (trigger == Trigger::release_key)
-        return true;
-
-    if (trigger == Trigger::release) {
-        const bool sostenutoed = isNoteSostenutoed(noteNumber);
-
-        if (sostenutoed && !sostenutoPressed) {
-            removeFromSostenutoReleases(noteNumber);
-            if (sustainPressed)
-                delaySustainRelease(noteNumber, midiState.getNoteVelocity(noteNumber));
-        }
-
-        if (!sostenutoPressed || !sostenutoed) {
-            if (sustainPressed)
-                delaySustainRelease(noteNumber, midiState.getNoteVelocity(noteNumber));
-            else
-                return true;
-        }
-    }
-
-    return false;
-}
-
-bool sfz::Region::registerCC(int ccNumber, float ccValue) noexcept
-{
-    ASSERT(ccValue >= 0.0f && ccValue <= 1.0f);
-
-    if (ccNumber == sustainCC)
-        sustainPressed = checkSustain && ccValue >= sustainThreshold;
-
-    if (ccNumber == sostenutoCC) {
-        const bool newState = checkSostenuto && ccValue >= sostenutoThreshold;
-        if (!sostenutoPressed && newState)
-            storeSostenutoNotes();
-
-        if (!newState && sostenutoPressed)
-            delayedSostenutoReleases.clear();
-
-        sostenutoPressed = newState;
-    }
-
-    if (ccConditions.getWithDefault(ccNumber).containsWithEnd(ccValue))
-        ccSwitched.set(ccNumber, true);
-    else
-        ccSwitched.set(ccNumber, false);
-
-    if (!isSwitchedOn())
-        return false;
-
-    if (!triggerOnCC)
-        return false;
-
-    if (ccTriggers.contains(ccNumber) && ccTriggers[ccNumber].containsWithEnd(ccValue))
-        return true;
-
-    return false;
-}
-
-void sfz::Region::registerPitchWheel(float pitch) noexcept
-{
-    if (bendRange.containsWithEnd(pitch))
-        pitchSwitched = true;
-    else
-        pitchSwitched = false;
-}
-
-void sfz::Region::registerAftertouch(float aftertouch) noexcept
-{
-    if (aftertouchRange.containsWithEnd(aftertouch))
-        aftertouchSwitched = true;
-    else
-        aftertouchSwitched = false;
-}
-
-void sfz::Region::registerTempo(float secondsPerQuarter) noexcept
-{
-    const float bpm = 60.0f / secondsPerQuarter;
-    if (bpmRange.containsWithEnd(bpm))
-        bpmSwitched = true;
-    else
-        bpmSwitched = false;
-}
-
 float sfz::Region::getBasePitchVariation(float noteNumber, float velocity) const noexcept
 {
     ASSERT(velocity >= 0.0f && velocity <= 1.0f);
@@ -1697,7 +1511,7 @@ float sfz::Region::getBasePitchVariation(float noteNumber, float velocity) const
     return centsFactor(pitchVariationInCents);
 }
 
-float sfz::Region::getBaseVolumedB(int noteNumber) const noexcept
+float sfz::Region::getBaseVolumedB(const MidiState& midiState, int noteNumber) const noexcept
 {
     fast_real_distribution<float> volumeDistribution { 0.0f, ampRandom };
     auto baseVolumedB = volume + volumeDistribution(Random::randomGenerator);
@@ -1732,7 +1546,7 @@ float sfz::Region::getPhase() const noexcept
     return phase;
 }
 
-uint64_t sfz::Region::getOffset(Oversampling factor) const noexcept
+uint64_t sfz::Region::getOffset(const MidiState& midiState, Oversampling factor) const noexcept
 {
     std::uniform_int_distribution<int64_t> offsetDistribution { 0, offsetRandom };
     uint64_t finalOffset = offset + offsetDistribution(Random::randomGenerator);
@@ -1741,7 +1555,7 @@ uint64_t sfz::Region::getOffset(Oversampling factor) const noexcept
     return Default::offset.bounds.clamp(finalOffset) * static_cast<uint64_t>(factor);
 }
 
-float sfz::Region::getDelay() const noexcept
+float sfz::Region::getDelay(const MidiState& midiState) const noexcept
 {
     fast_real_distribution<float> delayDistribution { 0, delayRandom };
     float finalDelay { delay };
@@ -1792,7 +1606,7 @@ float sfz::Region::getNoteGain(int noteNumber, float velocity) const noexcept
     return baseGain;
 }
 
-float sfz::Region::getCrossfadeGain() const noexcept
+float sfz::Region::getCrossfadeGain(const MidiState& midiState) const noexcept
 {
     float gain { 1.0f };
 
diff --git a/src/sfizz/Region.h b/src/sfizz/Region.h
index 4b3f106d..8c77d145 100644
--- a/src/sfizz/Region.h
+++ b/src/sfizz/Region.h
@@ -15,7 +15,6 @@
 #include "LFODescription.h"
 #include "Opcode.h"
 #include "AudioBuffer.h"
-#include "MidiState.h"
 #include "FileId.h"
 #include "utility/NumericId.h"
 #include "utility/LeakDetector.h"
@@ -29,6 +28,7 @@
 namespace sfz {
 
 class RegionSet;
+class MidiState;
 
 /**
  * @brief Regions are the basic building blocks for the SFZ parsing and handling code.
@@ -43,7 +43,7 @@ class RegionSet;
  *
  */
 struct Region {
-    Region(int regionNumber, const MidiState& midiState, absl::string_view defaultPath = "");
+    explicit Region(int regionNumber, absl::string_view defaultPath = "");
     Region(const Region&) = default;
     ~Region() = default;
 
@@ -98,65 +98,6 @@ struct Region {
      * @return false
      */
     bool shouldLoop() const noexcept { return (loopMode == LoopMode::loop_continuous || loopMode == LoopMode::loop_sustain); }
-    /**
-     * @brief Given the current midi state, is the region switched on?
-     *
-     * @return true
-     * @return false
-     */
-    bool isSwitchedOn() const noexcept;
-    /**
-     * @brief Register a new note on event. The region may be switched on or off using keys so
-     * this function updates the keyswitches state.
-     *
-     * @param noteNumber
-     * @param velocity
-     * @param randValue a random value between 0 and 1 used to randomize a bit the region activations
-     *                  and vary the samples
-     * @return true if the region should trigger on this event.
-     * @return false
-     */
-    bool registerNoteOn(int noteNumber, float velocity, float randValue) noexcept;
-    /**
-     * @brief Register a new note off event. The region may be switched on or off using keys so
-     * this function updates the keyswitches state.
-     *
-     * @param noteNumber
-     * @param velocity
-     * @param randValue a random value between 0 and 1 used to randomize a bit the region activations
-     *                  and vary the samples
-     * @return true if the region should trigger on this event.
-     * @return false
-     */
-    bool registerNoteOff(int noteNumber, float velocity, float randValue) noexcept;
-    /**
-     * @brief Register a new CC event. The region may be switched on or off using CCs so
-     * this function checks if it indeeds need to activate or not.
-     *
-     * @param ccNumber
-     * @param ccValue
-     * @return true if the region should trigger on this event
-     * @return false
-     */
-    bool registerCC(int ccNumber, float ccValue) noexcept;
-    /**
-     * @brief Register a new pitch wheel event.
-     *
-     * @param pitch
-     */
-    void registerPitchWheel(float pitch) noexcept;
-    /**
-     * @brief Register a new aftertouch event.
-     *
-     * @param aftertouch
-     */
-    void registerAftertouch(float aftertouch) noexcept;
-    /**
-     * @brief Register tempo
-     *
-     * @param secondsPerQuarter
-     */
-    void registerTempo(float secondsPerQuarter) noexcept;
 
     /**
      * @brief Get the base pitch of the region depending on which note has been
@@ -180,18 +121,19 @@ struct Region {
      * @brief Get the additional crossfade gain of the region depending on the
      * CC values
      *
-     * @param ccState
+     * @param midiState
      * @return float
      */
-    float getCrossfadeGain() const noexcept;
+    float getCrossfadeGain(const MidiState& midiState) const noexcept;
     /**
      * @brief Get the base volume of the region depending on which note has been
      * pressed to trigger the region.
      *
+     * @param midiState
      * @param noteNumber
      * @return float
      */
-    float getBaseVolumedB(int noteNumber) const noexcept;
+    float getBaseVolumedB(const MidiState& midiState, int noteNumber) const noexcept;
     /**
      * @brief Get the base gain of the region.
      *
@@ -221,15 +163,17 @@ struct Region {
     /**
      * @brief Get the region offset in samples
      *
+     * @param midiState
      * @return uint32_t
      */
-    uint64_t getOffset(Oversampling factor = Oversampling::x1) const noexcept;
+    uint64_t getOffset(const MidiState& midiState, Oversampling factor = Oversampling::x1) const noexcept;
     /**
      * @brief Get the region delay in seconds
      *
+     * @param midiState
      * @return float
      */
-    float getDelay() const noexcept;
+    float getDelay(const MidiState& midiState) const noexcept;
     /**
      * @brief Get the index of the sample end, either natural end or forced
      * loop.
@@ -410,6 +354,9 @@ struct Region {
     float sustainThreshold { Default::sustainThreshold }; // sustain_cc
     float sostenutoThreshold { Default::sostenutoThreshold }; // sustain_cc
 
+    bool usesKeySwitches { false };
+    bool usesPreviousKeySwitches { false };
+
     // Region logic: internal conditions
     UncheckedRange<float> aftertouchRange { Default::loChannelAftertouch, Default::hiChannelAftertouch }; // hichanaft and lochanaft
     UncheckedRange<float> bpmRange { Default::loBPM, Default::hiBPM }; // hibpm and lobpm
@@ -417,6 +364,8 @@ struct Region {
     uint8_t sequenceLength { Default::sequence }; // seq_length
     uint8_t sequencePosition { Default::sequence }; // seq_position
 
+    bool usesSequenceSwitches { false };
+
     // Region logic: triggers
     Trigger trigger { Default::trigger }; // trigger
     CCMap<UncheckedRange<float>> ccTriggers {{ Default::loCC, Default::hiCC }}; // on_loccN on_hiccN
@@ -507,29 +456,8 @@ struct Region {
     // Parent
     RegionSet* parent { nullptr };
 
-    // Started notes
-    bool sustainPressed { false };
-    bool sostenutoPressed { false };
-    std::vector<std::pair<int, float>> delayedSustainReleases;
-    std::vector<std::pair<int, float>> delayedSostenutoReleases;
-    void delaySustainRelease(int noteNumber, float velocity) noexcept;
-    void delaySostenutoRelease(int noteNumber, float velocity) noexcept;
-    void storeSostenutoNotes() noexcept;
-    void removeFromSostenutoReleases(int noteNumber) noexcept;
-    bool isNoteSustained(int noteNumber) const noexcept;
-    bool isNoteSostenutoed(int noteNumber) const noexcept;
+    std::string defaultPath;
 
-    const MidiState& midiState;
-    bool keySwitched { true };
-    bool previousKeySwitched { true };
-    bool sequenceSwitched { true };
-    bool pitchSwitched { true };
-    bool bpmSwitched { true };
-    bool aftertouchSwitched { true };
-    std::bitset<config::numCCs> ccSwitched;
-    std::string defaultPath { "" };
-
-    int sequenceCounter { 0 };
     LEAK_DETECTOR(Region);
 };
 
diff --git a/src/sfizz/Synth.cpp b/src/sfizz/Synth.cpp
index 0bcdfaf9..ca3b0245 100644
--- a/src/sfizz/Synth.cpp
+++ b/src/sfizz/Synth.cpp
@@ -136,8 +136,10 @@ void Synth::Impl::onParseWarning(const SourceRange& range, const std::string& me
 
 void Synth::Impl::buildRegion(const std::vector<Opcode>& regionOpcodes)
 {
-    int regionNumber = static_cast<int>(regions_.size());
-    auto lastRegion = absl::make_unique<Region>(regionNumber, resources_.midiState, defaultPath_);
+    int regionNumber = static_cast<int>(layers_.size());
+    Region* lastRegion = new Region(regionNumber, defaultPath_);
+    Layer* lastLayer = new Layer(std::unique_ptr<Region>(lastRegion), resources_.midiState);
+    layers_.emplace_back(lastLayer);
 
     //
     auto parseOpcodes = [&](const std::vector<Opcode>& opcodes) {
@@ -171,22 +173,22 @@ void Synth::Impl::buildRegion(const std::vector<Opcode>& regionOpcodes)
         lastRegion->offsetAllKeys(octaveOffset_ * 12 + noteOffset_);
 
     if (lastRegion->lastKeyswitch)
-        lastKeyswitchLists_[*lastRegion->lastKeyswitch].push_back(lastRegion.get());
+        lastKeyswitchLists_[*lastRegion->lastKeyswitch].push_back(lastLayer);
 
     if (lastRegion->lastKeyswitchRange) {
         auto& range = *lastRegion->lastKeyswitchRange;
         for (uint8_t note = range.getStart(), end = range.getEnd(); note <= end; note++)
-            lastKeyswitchLists_[note].push_back(lastRegion.get());
+            lastKeyswitchLists_[note].push_back(lastLayer);
     }
 
     if (lastRegion->upKeyswitch)
-        upKeyswitchLists_[*lastRegion->upKeyswitch].push_back(lastRegion.get());
+        upKeyswitchLists_[*lastRegion->upKeyswitch].push_back(lastLayer);
 
     if (lastRegion->downKeyswitch)
-        downKeyswitchLists_[*lastRegion->downKeyswitch].push_back(lastRegion.get());
+        downKeyswitchLists_[*lastRegion->downKeyswitch].push_back(lastLayer);
 
     if (lastRegion->previousKeyswitch)
-        previousKeyswitchLists_.push_back(lastRegion.get());
+        previousKeyswitchLists_.push_back(lastLayer);
 
     if (lastRegion->defaultSwitch)
         currentSwitch_ = *lastRegion->defaultSwitch;
@@ -201,18 +203,19 @@ void Synth::Impl::buildRegion(const std::vector<Opcode>& regionOpcodes)
 
     if (currentSet_ != nullptr) {
         lastRegion->parent = currentSet_;
-        currentSet_->addRegion(lastRegion.get());
+        currentSet_->addRegion(lastRegion);
     }
 
     // Adapt the size of the delayed releases to avoid allocating later on
     if (lastRegion->trigger == Trigger::release) {
         const auto keyLength = static_cast<unsigned>(lastRegion->keyRange.length());
         const auto size = max(config::delayedReleaseVoices, keyLength);
-        lastRegion->delayedSustainReleases.reserve(size);
-        lastRegion->delayedSostenutoReleases.reserve(size);
+        lastLayer->delayedSustainReleases_.reserve(size);
+        lastLayer->delayedSostenutoReleases_.reserve(size);
     }
 
-    regions_.push_back(std::move(lastRegion));
+    // Initialize status of Key switches, CC switches, etc
+    lastLayer->initializeActivations();
 }
 
 void Synth::Impl::clear()
@@ -235,7 +238,7 @@ void Synth::Impl::clear()
 
     currentSet_ = nullptr;
     sets_.clear();
-    regions_.clear();
+    layers_.clear();
     effectBuses_.clear();
     effectBuses_.emplace_back(new EffectBus);
     effectBuses_[0]->setGainToMain(1.0);
@@ -502,7 +505,7 @@ bool Synth::loadSfzFile(const fs::path& file)
     if (!loaderParsesPermissively)
         success = parser.getErrorCount() == 0;
 
-    success = success && !impl.regions_.empty();
+    success = success && !impl.layers_.empty();
 
     if (!success) {
         parser.clear();
@@ -527,7 +530,7 @@ bool Synth::loadSfzString(const fs::path& path, absl::string_view text)
     if (!loaderParsesPermissively)
         success = parser.getErrorCount() == 0;
 
-    success = success && !impl.regions_.empty();
+    success = success && !impl.layers_.empty();
 
     if (!success) {
         parser.clear();
@@ -543,11 +546,12 @@ void Synth::Impl::finalizeSfzLoad()
     resources_.filePool.setRootDirectory(parser_.originalDirectory());
 
     size_t currentRegionIndex = 0;
-    size_t currentRegionCount = regions_.size();
+    size_t currentRegionCount = layers_.size();
 
     auto removeCurrentRegion = [this, &currentRegionIndex, &currentRegionCount]() {
-        DBG("Removing the region with sample " << *regions_[currentRegionIndex]->sampleId);
-        regions_.erase(regions_.begin() + currentRegionIndex);
+        const Region& region = layers_[currentRegionIndex]->getRegion();
+        DBG("Removing the region with sample " << *region.sampleId);
+        layers_.erase(layers_.begin() + currentRegionIndex);
         --currentRegionCount;
     };
 
@@ -564,155 +568,156 @@ void Synth::Impl::finalizeSfzLoad()
     FlexEGs::clearUnusedCurves();
 
     while (currentRegionIndex < currentRegionCount) {
-        auto region = regions_[currentRegionIndex].get();
+        Layer& layer = *layers_[currentRegionIndex];
+        Region& region = layer.getRegion();
 
         absl::optional<FileInformation> fileInformation;
 
-        if (!region->isGenerator()) {
-            if (!resources_.filePool.checkSampleId(*region->sampleId)) {
+        if (!region.isGenerator()) {
+            if (!resources_.filePool.checkSampleId(*region.sampleId)) {
                 removeCurrentRegion();
                 continue;
             }
 
-            fileInformation = resources_.filePool.getFileInformation(*region->sampleId);
+            fileInformation = resources_.filePool.getFileInformation(*region.sampleId);
             if (!fileInformation) {
                 removeCurrentRegion();
                 continue;
             }
 
-            region->hasWavetableSample = fileInformation->wavetable ||
+            region.hasWavetableSample = fileInformation->wavetable ||
                 fileInformation->end < config::wavetableMaxFrames;
         }
 
-        if (!region->isOscillator()) {
-            region->sampleEnd = std::min(region->sampleEnd, fileInformation->end);
+        if (!region.isOscillator()) {
+            region.sampleEnd = std::min(region.sampleEnd, fileInformation->end);
 
             if (fileInformation->hasLoop) {
-                if (region->loopRange.getStart() == Default::loopStart)
-                    region->loopRange.setStart(fileInformation->loopStart);
+                if (region.loopRange.getStart() == Default::loopStart)
+                    region.loopRange.setStart(fileInformation->loopStart);
 
-                if (region->loopRange.getEnd() == Default::loopEnd)
-                    region->loopRange.setEnd(fileInformation->loopEnd);
+                if (region.loopRange.getEnd() == Default::loopEnd)
+                    region.loopRange.setEnd(fileInformation->loopEnd);
 
-                if (!region->loopMode)
-                    region->loopMode = LoopMode::loop_continuous;
+                if (!region.loopMode)
+                    region.loopMode = LoopMode::loop_continuous;
             }
 
-            if (region->isRelease() && !region->loopMode)
-                region->loopMode = LoopMode::one_shot;
+            if (region.isRelease() && !region.loopMode)
+                region.loopMode = LoopMode::one_shot;
 
-            if (region->loopRange.getEnd() == Default::loopEnd)
-                region->loopRange.setEnd(region->sampleEnd);
+            if (region.loopRange.getEnd() == Default::loopEnd)
+                region.loopRange.setEnd(region.sampleEnd);
 
             // if range is invalid, disable the loop
-            if (!region->loopRange.isValid())
-                region->loopMode = absl::nullopt;
+            if (!region.loopRange.isValid())
+                region.loopMode = absl::nullopt;
 
             if (fileInformation->numChannels == 2)
-                region->hasStereoSample = true;
+                region.hasStereoSample = true;
 
-            if (region->pitchKeycenterFromSample)
-                region->pitchKeycenter = fileInformation->rootKey;
+            if (region.pitchKeycenterFromSample)
+                region.pitchKeycenter = fileInformation->rootKey;
 
             // TODO: adjust with LFO targets
             const auto maxOffset = [region]() {
-                uint64_t sumOffsetCC = region->offset + region->offsetRandom;
-                for (const auto& offsets : region->offsetCC)
+                uint64_t sumOffsetCC = region.offset + region.offsetRandom;
+                for (const auto& offsets : region.offsetCC)
                     sumOffsetCC += offsets.data;
                 return Default::offsetMod.bounds.clamp(sumOffsetCC);
             }();
 
-            if (!resources_.filePool.preloadFile(*region->sampleId, maxOffset))
+            if (!resources_.filePool.preloadFile(*region.sampleId, maxOffset))
                 removeCurrentRegion();
         }
-        else if (!region->isGenerator()) {
-            if (!resources_.wavePool.createFileWave(resources_.filePool, std::string(region->sampleId->filename()))) {
+        else if (!region.isGenerator()) {
+            if (!resources_.wavePool.createFileWave(resources_.filePool, std::string(region.sampleId->filename()))) {
                 removeCurrentRegion();
                 continue;
             }
         }
 
-        if (region->lastKeyswitch) {
+        if (region.lastKeyswitch) {
             if (currentSwitch_)
-                region->keySwitched = (*currentSwitch_ == *region->lastKeyswitch);
+                layer.keySwitched_ = (*currentSwitch_ == *region.lastKeyswitch);
 
-            if (region->keyswitchLabel)
-                setKeyswitchLabel(*region->lastKeyswitch, *region->keyswitchLabel);
+            if (region.keyswitchLabel)
+                setKeyswitchLabel(*region.lastKeyswitch, *region.keyswitchLabel);
         }
 
-        if (region->lastKeyswitchRange) {
-            auto& range = *region->lastKeyswitchRange;
+        if (region.lastKeyswitchRange) {
+            auto& range = *region.lastKeyswitchRange;
             if (currentSwitch_)
-                region->keySwitched = range.containsWithEnd(*currentSwitch_);
+                layer.keySwitched_ = range.containsWithEnd(*currentSwitch_);
 
-            if (region->keyswitchLabel) {
+            if (region.keyswitchLabel) {
                 for (uint8_t note = range.getStart(), end = range.getEnd(); note <= end; note++)
-                    setKeyswitchLabel(note, *region->keyswitchLabel);
+                    setKeyswitchLabel(note, *region.keyswitchLabel);
             }
         }
 
         for (auto note = 0; note < 128; note++) {
-            if (region->keyRange.containsWithEnd(note))
-                noteActivationLists_[note].push_back(region);
+            if (region.keyRange.containsWithEnd(note))
+                noteActivationLists_[note].push_back(&layer);
         }
 
         for (int cc = 0; cc < config::numCCs; cc++) {
-            if (region->ccTriggers.contains(cc)
-                || region->ccConditions.contains(cc)
-                || (cc == region->sustainCC && region->trigger == Trigger::release)
-                || (cc == region->sostenutoCC && region->trigger == Trigger::release))
-                ccActivationLists_[cc].push_back(region);
+            if (region.ccTriggers.contains(cc)
+                || region.ccConditions.contains(cc)
+                || (cc == region.sustainCC && region.trigger == Trigger::release)
+                || (cc == region.sostenutoCC && region.trigger == Trigger::release))
+                ccActivationLists_[cc].push_back(&layer);
         }
 
         // Defaults
         for (int cc = 0; cc < config::numCCs; cc++) {
-            region->registerCC(cc, resources_.midiState.getCCValue(cc));
+            layer.registerCC(cc, resources_.midiState.getCCValue(cc));
         }
 
 
         // Set the default frequencies on equalizers if needed
-        if (region->equalizers.size() > 0
-            && region->equalizers[0].frequency == Default::eqFrequency) {
-            region->equalizers[0].frequency = Default::defaultEQFreq[0];
-            if (region->equalizers.size() > 1
-                && region->equalizers[1].frequency == Default::eqFrequency) {
-                region->equalizers[1].frequency = Default::defaultEQFreq[1];
-                if (region->equalizers.size() > 2
-                    && region->equalizers[2].frequency == Default::eqFrequency) {
-                    region->equalizers[2].frequency = Default::defaultEQFreq[2];
+        if (region.equalizers.size() > 0
+            && region.equalizers[0].frequency == Default::eqFrequency) {
+            region.equalizers[0].frequency = Default::defaultEQFreq[0];
+            if (region.equalizers.size() > 1
+                && region.equalizers[1].frequency == Default::eqFrequency) {
+                region.equalizers[1].frequency = Default::defaultEQFreq[1];
+                if (region.equalizers.size() > 2
+                    && region.equalizers[2].frequency == Default::eqFrequency) {
+                    region.equalizers[2].frequency = Default::defaultEQFreq[2];
                 }
             }
         }
 
-        if (!region->velocityPoints.empty())
-            region->velCurve = Curve::buildFromVelcurvePoints(
-                region->velocityPoints, Curve::Interpolator::Linear);
+        if (!region.velocityPoints.empty())
+            region.velCurve = Curve::buildFromVelcurvePoints(
+                region.velocityPoints, Curve::Interpolator::Linear);
 
-        region->registerPitchWheel(0);
-        region->registerAftertouch(0);
-        region->registerTempo(2.0f);
-        maxFilters = max(maxFilters, region->filters.size());
-        maxEQs = max(maxEQs, region->equalizers.size());
-        maxLFOs = max(maxLFOs, region->lfos.size());
-        maxFlexEGs = max(maxFlexEGs, region->flexEGs.size());
-        havePitchEG = havePitchEG || region->pitchEG != absl::nullopt;
-        haveFilterEG = haveFilterEG || region->filterEG != absl::nullopt;
-        haveAmplitudeLFO = haveAmplitudeLFO || region->amplitudeLFO != absl::nullopt;
-        havePitchLFO = havePitchLFO || region->pitchLFO != absl::nullopt;
-        haveFilterLFO = haveFilterLFO || region->filterLFO != absl::nullopt;
+        layer.registerPitchWheel(0);
+        layer.registerAftertouch(0);
+        layer.registerTempo(2.0f);
+        maxFilters = max(maxFilters, region.filters.size());
+        maxEQs = max(maxEQs, region.equalizers.size());
+        maxLFOs = max(maxLFOs, region.lfos.size());
+        maxFlexEGs = max(maxFlexEGs, region.flexEGs.size());
+        havePitchEG = havePitchEG || region.pitchEG != absl::nullopt;
+        haveFilterEG = haveFilterEG || region.filterEG != absl::nullopt;
+        haveAmplitudeLFO = haveAmplitudeLFO || region.amplitudeLFO != absl::nullopt;
+        havePitchLFO = havePitchLFO || region.pitchLFO != absl::nullopt;
+        haveFilterLFO = haveFilterLFO || region.filterLFO != absl::nullopt;
 
         ++currentRegionIndex;
     }
-    if (currentRegionCount < regions_.size()) {
-        DBG("Removing " << (regions_.size() - currentRegionCount)
-            << " out of " << regions_.size() << " regions");
+    if (currentRegionCount < layers_.size()) {
+        DBG("Removing " << (layers_.size() - currentRegionCount)
+            << " out of " << layers_.size() << " regions");
     }
-    regions_.resize(currentRegionCount);
+    layers_.resize(currentRegionCount);
 
     // collect all CCs used in regions, with matrix not yet connected
     BitArray<config::numCCs> usedCCs;
-    for (const RegionPtr& regionPtr : regions_) {
-        const Region& region = *regionPtr;
+    for (const LayerPtr& layerPtr : layers_) {
+        const Region& region = layerPtr->getRegion();
         collectUsedCCsFromRegion(usedCCs, region);
         for (const Region::Connection& connection : region.connections) {
             if (connection.source.id() == ModId::Controller)
@@ -720,8 +725,8 @@ void Synth::Impl::finalizeSfzLoad()
         }
     }
     // connect default controllers, except if these CC are already used
-    for (const RegionPtr& regionPtr : regions_) {
-        Region& region = *regionPtr;
+    for (const LayerPtr& layerPtr : layers_) {
+        Region& region = layerPtr->getRegion();
         constexpr unsigned defaultSmoothness = 10;
         if (!usedCCs.test(7)) {
             region.getOrCreateConnection(
@@ -760,19 +765,21 @@ void Synth::Impl::finalizeSfzLoad()
     currentUsedCCs_ = collectAllUsedCCs();
 
     // cache the set of keys assigned
-    for (const RegionPtr& regionPtr : regions_) {
-        UncheckedRange<uint8_t> keyRange = regionPtr->keyRange;
+    for (const LayerPtr& layerPtr : layers_) {
+        const Region& region = layerPtr->getRegion();
+        UncheckedRange<uint8_t> keyRange = region.keyRange;
         unsigned loKey = keyRange.getStart();
         unsigned hiKey = keyRange.getEnd();
         for (unsigned key = loKey; key <= hiKey; ++key)
             keySlots_.set(key);
     }
     // cache the set of keyswitches assigned
-    for (const RegionPtr& regionPtr : regions_) {
-        if (absl::optional<uint8_t> sw = regionPtr->lastKeyswitch) {
+    for (const LayerPtr& layerPtr : layers_) {
+        const Region& region = layerPtr->getRegion();
+        if (absl::optional<uint8_t> sw = region.lastKeyswitch) {
             swLastSlots_.set(*sw);
         }
-        else if (absl::optional<UncheckedRange<uint8_t>> swRange = regionPtr->lastKeyswitchRange) {
+        else if (absl::optional<UncheckedRange<uint8_t>> swRange = region.lastKeyswitchRange) {
             unsigned loKey = swRange->getStart();
             unsigned hiKey = swRange->getEnd();
             for (unsigned key = loKey; key <= hiKey; ++key)
@@ -1075,15 +1082,17 @@ void Synth::noteOff(int delay, int noteNumber, uint8_t velocity) noexcept
     impl.resources_.midiState.noteOffEvent(delay, noteNumber, normalizedVelocity);
 }
 
-void Synth::Impl::startVoice(Region* region, int delay, const TriggerEvent& triggerEvent, SisterVoiceRingBuilder& ring) noexcept
+void Synth::Impl::startVoice(Layer* layer, int delay, const TriggerEvent& triggerEvent, SisterVoiceRingBuilder& ring) noexcept
 {
-    voiceManager_.checkPolyphony(region, delay, triggerEvent);
+    const Region& region = layer->getRegion();
+
+    voiceManager_.checkPolyphony(&region, delay, triggerEvent);
     Voice* selectedVoice = voiceManager_.findFreeVoice();
     if (selectedVoice == nullptr)
         return;
 
     ASSERT(selectedVoice->isFree());
-    if (selectedVoice->startVoice(region, delay, triggerEvent))
+    if (selectedVoice->startVoice(layer, delay, triggerEvent))
         ring.addVoiceToRing(selectedVoice);
 }
 
@@ -1093,18 +1102,19 @@ void Synth::Impl::noteOffDispatch(int delay, int noteNumber, float velocity) noe
     SisterVoiceRingBuilder ring;
     const TriggerEvent triggerEvent { TriggerEventType::NoteOff, noteNumber, velocity };
 
-    for (auto& region : upKeyswitchLists_[noteNumber])
-        region->keySwitched = true;
+    for (Layer* layer : upKeyswitchLists_[noteNumber])
+        layer->keySwitched_ = true;
 
-    for (auto& region : downKeyswitchLists_[noteNumber])
-        region->keySwitched = false;
+    for (Layer* layer : downKeyswitchLists_[noteNumber])
+        layer->keySwitched_ = false;
 
-    for (auto& region : noteActivationLists_[noteNumber]) {
-        if (region->registerNoteOff(noteNumber, velocity, randValue)) {
-            if (region->trigger == Trigger::release && !region->rtDead && !voiceManager_.playingAttackVoice(region))
+    for (Layer* layer : noteActivationLists_[noteNumber]) {
+        const Region& region = layer->getRegion();
+        if (layer->registerNoteOff(noteNumber, velocity, randValue)) {
+            if (region.trigger == Trigger::release && !region.rtDead && !voiceManager_.playingAttackVoice(&region))
                 continue;
 
-            startVoice(region, delay, triggerEvent, ring);
+            startVoice(layer, delay, triggerEvent, ring);
         }
     }
 }
@@ -1116,70 +1126,77 @@ void Synth::Impl::noteOnDispatch(int delay, int noteNumber, float velocity) noex
 
     if (!lastKeyswitchLists_[noteNumber].empty()) {
         if (currentSwitch_ && *currentSwitch_ != noteNumber) {
-            for (auto& region : lastKeyswitchLists_[*currentSwitch_])
-                region->keySwitched = false;
+            for (Layer* layer : lastKeyswitchLists_[*currentSwitch_])
+                layer->keySwitched_ = false;
         }
         currentSwitch_ = noteNumber;
         currentSwitchChanged_ = true;
     }
 
-    for (auto& region : lastKeyswitchLists_[noteNumber])
-        region->keySwitched = true;
+    for (Layer* layer : lastKeyswitchLists_[noteNumber])
+        layer->keySwitched_ = true;
 
-    for (auto& region : upKeyswitchLists_[noteNumber])
-        region->keySwitched = false;
+    for (Layer* layer : upKeyswitchLists_[noteNumber])
+        layer->keySwitched_ = false;
 
-    for (auto& region : downKeyswitchLists_[noteNumber])
-        region->keySwitched = true;
+    for (Layer* layer : downKeyswitchLists_[noteNumber])
+        layer->keySwitched_ = true;
 
-    for (auto& region : noteActivationLists_[noteNumber]) {
-        if (region->registerNoteOn(noteNumber, velocity, randValue)) {
+    for (Layer* layer : noteActivationLists_[noteNumber]) {
+        if (layer->registerNoteOn(noteNumber, velocity, randValue)) {
+            const Region& region = layer->getRegion();
             for (auto& voice : voiceManager_) {
-                if (voice.checkOffGroup(region, delay, noteNumber)) {
+                if (voice.checkOffGroup(&region, delay, noteNumber)) {
                     const TriggerEvent& event = voice.getTriggerEvent();
                     noteOffDispatch(delay, event.number, event.value);
                 }
             }
 
             TriggerEvent triggerEvent { TriggerEventType::NoteOn, noteNumber, velocity };
-            if (region->velocityOverride == VelocityOverride::previous)
+            if (region.velocityOverride == VelocityOverride::previous)
                 triggerEvent.value = resources_.midiState.getLastVelocity();
 
-            startVoice(region, delay, triggerEvent, ring);
+            startVoice(layer, delay, triggerEvent, ring);
         }
     }
 
-    for (auto& region : previousKeyswitchLists_)
-        region->previousKeySwitched = (*region->previousKeyswitch == noteNumber);
+    for (Layer* layer : previousKeyswitchLists_) {
+        const Region& region = layer->getRegion();
+        layer->previousKeySwitched_ = (region.previousKeyswitch == noteNumber);
+    }
 }
 
-void Synth::Impl::startDelayedSustainReleases(Region* region, int delay, SisterVoiceRingBuilder& ring) noexcept
+void Synth::Impl::startDelayedSustainReleases(Layer* layer, int delay, SisterVoiceRingBuilder& ring) noexcept
 {
-    if (!region->rtDead && !voiceManager_.playingAttackVoice(region)) {
-        region->delayedSustainReleases.clear();
+    const Region& region = layer->getRegion();
+
+    if (!region.rtDead && !voiceManager_.playingAttackVoice(&region)) {
+        layer->delayedSustainReleases_.clear();
         return;
     }
 
-    for (auto& note: region->delayedSustainReleases) {
+    for (auto& note: layer->delayedSustainReleases_) {
         const TriggerEvent noteOffEvent { TriggerEventType::NoteOff, note.first, note.second };
-        startVoice(region, delay, noteOffEvent, ring);
+        startVoice(layer, delay, noteOffEvent, ring);
     }
 
-    region->delayedSustainReleases.clear();
+    layer->delayedSustainReleases_.clear();
 }
 
-void Synth::Impl::startDelayedSostenutoReleases(Region* region, int delay, SisterVoiceRingBuilder& ring) noexcept
+void Synth::Impl::startDelayedSostenutoReleases(Layer* layer, int delay, SisterVoiceRingBuilder& ring) noexcept
 {
-    if (!region->rtDead && !voiceManager_.playingAttackVoice(region)) {
-        region->delayedSostenutoReleases.clear();
+    const Region& region = layer->getRegion();
+
+    if (!region.rtDead && !voiceManager_.playingAttackVoice(&region)) {
+        layer->delayedSostenutoReleases_.clear();
         return;
     }
 
-    for (auto& note: region->delayedSostenutoReleases) {
+    for (auto& note: layer->delayedSostenutoReleases_) {
         const TriggerEvent noteOffEvent { TriggerEventType::NoteOff, note.first, note.second };
-        startVoice(region, delay, noteOffEvent, ring);
+        startVoice(layer, delay, noteOffEvent, ring);
     }
-    region->delayedSostenutoReleases.clear();
+    layer->delayedSostenutoReleases_.clear();
 }
 
 void Synth::cc(int delay, int ccNumber, uint8_t ccValue) noexcept
@@ -1192,23 +1209,25 @@ void Synth::Impl::ccDispatch(int delay, int ccNumber, float value) noexcept
 {
     SisterVoiceRingBuilder ring;
     const TriggerEvent triggerEvent { TriggerEventType::CC, ccNumber, value };
-    for (auto& region : ccActivationLists_[ccNumber]) {
-        if (region->checkSustain && ccNumber == region->sustainCC && value < region->sustainThreshold)
-            startDelayedSustainReleases(region, delay, ring);
+    for (Layer* layer : ccActivationLists_[ccNumber]) {
+        const Region& region = layer->getRegion();
 
-        if (region->checkSostenuto && ccNumber == region->sostenutoCC && value < region->sostenutoThreshold) {
-            if (region->sustainPressed) {
-                for (const auto& v: region->delayedSostenutoReleases)
-                    region->delaySustainRelease(v.first, v.second);
+        if (region.checkSustain && ccNumber == region.sustainCC && value < region.sustainThreshold)
+            startDelayedSustainReleases(layer, delay, ring);
 
-                region->delayedSostenutoReleases.clear();
+        if (region.checkSostenuto && ccNumber == region.sostenutoCC && value < region.sostenutoThreshold) {
+            if (layer->sustainPressed_) {
+                for (const auto& v: layer->delayedSostenutoReleases_)
+                    layer->delaySustainRelease(v.first, v.second);
+
+                layer->delayedSostenutoReleases_.clear();
             } else {
-                startDelayedSostenutoReleases(region, delay, ring);
+                startDelayedSostenutoReleases(layer, delay, ring);
             }
         }
 
-        if (region->registerCC(ccNumber, value))
-            startVoice(region, delay, triggerEvent, ring);
+        if (layer->registerCC(ccNumber, value))
+            startVoice(layer, delay, triggerEvent, ring);
     }
 }
 
@@ -1288,8 +1307,8 @@ void Synth::pitchWheel(int delay, int pitch) noexcept
     ScopedTiming logger { impl.dispatchDuration_, ScopedTiming::Operation::addToDuration };
     impl.resources_.midiState.pitchBendEvent(delay, normalizedPitch);
 
-    for (auto& region : impl.regions_) {
-        region->registerPitchWheel(normalizedPitch);
+    for (const Impl::LayerPtr& layer : impl.layers_) {
+        layer->registerPitchWheel(normalizedPitch);
     }
 
     for (auto& voice : impl.voiceManager_) {
@@ -1310,8 +1329,8 @@ void Synth::hdAftertouch(int delay, float normAftertouch) noexcept
 
     impl.resources_.midiState.channelAftertouchEvent(delay, normAftertouch);
 
-    for (auto& region : impl.regions_) {
-        region->registerAftertouch(normAftertouch);
+    for (const Impl::LayerPtr& layerPtr : impl.layers_) {
+        layerPtr->registerAftertouch(normAftertouch);
     }
 
     for (auto& voice : impl.voiceManager_) {
@@ -1365,7 +1384,7 @@ void Synth::playbackState(int delay, int playbackState)
 int Synth::getNumRegions() const noexcept
 {
     Impl& impl = *impl_;
-    return static_cast<int>(impl.regions_.size());
+    return static_cast<int>(impl.layers_.size());
 }
 
 int Synth::getNumGroups() const noexcept
@@ -1490,10 +1509,16 @@ std::string Synth::exportMidnam(absl::string_view model) const
     return std::move(writer.str());
 }
 
-const Region* Synth::getRegionView(int idx) const noexcept
+const Layer* Synth::getLayerView(int idx) const noexcept
 {
     Impl& impl = *impl_;
-    return (size_t)idx < impl.regions_.size() ? impl.regions_[idx].get() : nullptr;
+    return (size_t)idx < impl.layers_.size() ? impl.layers_[idx].get() : nullptr;
+}
+
+const Region* Synth::getRegionView(int idx) const noexcept
+{
+    const Layer* layer = getLayerView(idx);
+    return layer ? &layer->getRegion() : nullptr;
 }
 
 const EffectBus* Synth::getEffectBusView(int idx) const noexcept
@@ -1514,10 +1539,10 @@ const PolyphonyGroup* Synth::getPolyphonyGroupView(int idx) const noexcept
     return impl.voiceManager_.getPolyphonyGroupView(idx);
 }
 
-const Region* Synth::getRegionById(NumericId<Region> id) const noexcept
+Layer* Synth::getLayerById(NumericId<Region> id) noexcept
 {
     Impl& impl = *impl_;
-    const size_t size = impl.regions_.size();
+    const size_t size = impl.layers_.size();
 
     if (size == 0 || !id.valid())
         return nullptr;
@@ -1526,10 +1551,17 @@ const Region* Synth::getRegionById(NumericId<Region> id) const noexcept
     size_t index = static_cast<size_t>(id.number());
     index = std::min(index, size - 1);
 
-    while (index > 0 && impl.regions_[index]->getId().number() > id.number())
+    while (index > 0 && impl.layers_[index]->getRegion().getId().number() > id.number())
         --index;
 
-    return (impl.regions_[index]->getId() == id) ? impl.regions_[index].get() : nullptr;
+    return (impl.layers_[index]->getRegion().getId() == id) ?
+        impl.layers_[index].get() : nullptr;
+}
+
+const Region* Synth::getRegionById(NumericId<Region> id) const noexcept
+{
+    Layer* layer = const_cast<Synth*>(this)->getLayerById(id);
+    return layer ? &layer->getRegion() : nullptr;
 }
 
 const Voice* Synth::getVoiceView(int idx) const noexcept
@@ -1653,8 +1685,10 @@ void Synth::Impl::setupModMatrix()
 {
     ModMatrix& mm = resources_.modMatrix;
 
-    for (const RegionPtr& region : regions_) {
-        for (const Region::Connection& conn : region->connections) {
+    for (const LayerPtr& layerPtr : layers_) {
+        const Region& region = layerPtr->getRegion();
+
+        for (const Region::Connection& conn : region.connections) {
             ModGenerator* gen = nullptr;
 
             ModKey sourceKey = conn.source;
@@ -1789,9 +1823,10 @@ void Synth::Impl::resetAllControllers(int delay) noexcept
             voice.registerCC(delay, cc, 0.0f);
     }
 
-    for (auto& region : regions_) {
+    for (const LayerPtr& layerPtr : layers_) {
+        Layer& layer = *layerPtr;
         for (int cc = 0; cc < config::numCCs; ++cc)
-            region->registerCC(cc, 0.0f);
+            layer.registerCC(cc, 0.0f);
     }
 }
 
@@ -1929,8 +1964,8 @@ void Synth::Impl::collectUsedCCsFromModulations(BitArray<config::numCCs>& usedCC
 BitArray<config::numCCs> Synth::Impl::collectAllUsedCCs()
 {
     BitArray<config::numCCs> used;
-    for (const Impl::RegionPtr& region : regions_)
-        collectUsedCCsFromRegion(used, *region);
+    for (const LayerPtr& layerPtr : layers_)
+        collectUsedCCsFromRegion(used, layerPtr->getRegion());
     collectUsedCCsFromModulations(used, resources_.modMatrix);
     return used;
 }
diff --git a/src/sfizz/Synth.h b/src/sfizz/Synth.h
index d314b9a0..5bdf3ba4 100644
--- a/src/sfizz/Synth.h
+++ b/src/sfizz/Synth.h
@@ -26,6 +26,7 @@ class RegionSet;
 class PolyphonyGroup;
 class EffectBus;
 struct Region;
+struct Layer;
 class Voice;
 
 /**
@@ -189,6 +190,13 @@ public:
      * @brief Export a MIDI Name document describing the loaded instrument
      */
     std::string exportMidnam(absl::string_view model = {}) const;
+    /**
+     * @brief Find the layer which is associated with the given identifier.
+     *
+     * @param id
+     * @return Layer*
+     */
+    Layer* getLayerById(NumericId<Region> id) noexcept;
     /**
      * @brief Find the region which is associated with the given identifier.
      *
@@ -196,6 +204,14 @@ public:
      * @return const Region*
      */
     const Region* getRegionById(NumericId<Region> id) const noexcept;
+    /**
+     * @brief Get a raw view into a specific layer. This is mostly used
+     * for testing.
+     *
+     * @param idx
+     * @return const Layer*
+     */
+    const Layer* getLayerView(int idx) const noexcept;
     /**
      * @brief Get a raw view into a specific region. This is mostly used
      * for testing.
diff --git a/src/sfizz/SynthMessaging.cpp b/src/sfizz/SynthMessaging.cpp
index a91b9447..24de4b96 100644
--- a/src/sfizz/SynthMessaging.cpp
+++ b/src/sfizz/SynthMessaging.cpp
@@ -28,9 +28,10 @@ void sfz::Synth::dispatchMessage(Client& client, int delay, const char* path, co
             if (extractMessage(p, path, indices) && !strcmp(sig, s))
 
         #define GET_REGION_OR_BREAK(idx)            \
-            if (idx >= impl.regions_.size())        \
+            if (idx >= impl.layers_.size())         \
                 break;                              \
-            const auto& region = *impl.regions_[idx];
+            Layer& layer = *impl.layers_[idx];      \
+            const Region& region = layer.getRegion();
 
         MATCH("/hello", "") {
             client.receive(delay, "/hello", "", nullptr);
diff --git a/src/sfizz/SynthPrivate.h b/src/sfizz/SynthPrivate.h
index b40ebcc7..350a12fd 100644
--- a/src/sfizz/SynthPrivate.h
+++ b/src/sfizz/SynthPrivate.h
@@ -5,6 +5,7 @@
 #include "SisterVoiceRing.h"
 #include "TriggerEvent.h"
 #include "VoiceManager.h"
+#include "Layer.h"
 #include "BitArray.h"
 #include "modulations/sources/ADSREnvelope.h"
 #include "modulations/sources/Controller.h"
@@ -147,30 +148,30 @@ struct Synth::Impl final: public Parser::Listener {
      * @brief Start a voice for a specific region.
      * This will do the needed polyphony checks and voice stealing.
      *
-     * @param region
+     * @param layer
      * @param delay
      * @param triggerEvent
      * @param ring
      */
-    void startVoice(Region* region, int delay, const TriggerEvent& triggerEvent, SisterVoiceRingBuilder& ring) noexcept;
+    void startVoice(Layer* layer, int delay, const TriggerEvent& triggerEvent, SisterVoiceRingBuilder& ring) noexcept;
 
     /**
      * @brief Start all delayed sustain release voices of the region if necessary
      *
-     * @param region
+     * @param layer
      * @param delay
      * @param ring
      */
-    void startDelayedSustainReleases(Region* region, int delay, SisterVoiceRingBuilder& ring) noexcept;
+    void startDelayedSustainReleases(Layer* layer, int delay, SisterVoiceRingBuilder& ring) noexcept;
 
     /**
      * @brief Start all delayed sostenuto release voices of the region if necessary
      *
-     * @param region
+     * @param layer
      * @param delay
      * @param ring
      */
-    void startDelayedSostenutoReleases(Region* region, int delay, SisterVoiceRingBuilder& ring) noexcept;
+    void startDelayedSostenutoReleases(Layer* layer, int delay, SisterVoiceRingBuilder& ring) noexcept;
 
     /**
      * @brief Finalize SFZ loading, following a successful execution of the
@@ -242,22 +243,24 @@ struct Synth::Impl final: public Parser::Listener {
     bool currentSwitchChanged_ = true;
     std::vector<std::string> unknownOpcodes_;
     using RegionViewVector = std::vector<Region*>;
+    using LayerViewVector = std::vector<Layer*>;
     using VoiceViewVector = std::vector<Voice*>;
+    using LayerPtr = std::unique_ptr<Layer>;
     using RegionPtr = std::unique_ptr<Region>;
     using RegionSetPtr = std::unique_ptr<RegionSet>;
-    std::vector<RegionPtr> regions_;
+    std::vector<LayerPtr> layers_;
     VoiceManager voiceManager_;
 
     // These are more general "groups" than sfz and encapsulates the full hierarchy
     RegionSet* currentSet_ { nullptr };
     std::vector<RegionSetPtr> sets_;
 
-    std::array<RegionViewVector, 128> lastKeyswitchLists_;
-    std::array<RegionViewVector, 128> downKeyswitchLists_;
-    std::array<RegionViewVector, 128> upKeyswitchLists_;
-    RegionViewVector previousKeyswitchLists_;
-    std::array<RegionViewVector, 128> noteActivationLists_;
-    std::array<RegionViewVector, config::numCCs> ccActivationLists_;
+    std::array<LayerViewVector, 128> lastKeyswitchLists_;
+    std::array<LayerViewVector, 128> downKeyswitchLists_;
+    std::array<LayerViewVector, 128> upKeyswitchLists_;
+    LayerViewVector previousKeyswitchLists_;
+    std::array<LayerViewVector, 128> noteActivationLists_;
+    std::array<LayerViewVector, config::numCCs> ccActivationLists_;
 
     // Effect factory and buses
     EffectFactory effectFactory_;
diff --git a/src/sfizz/Voice.cpp b/src/sfizz/Voice.cpp
index e2eb1f30..06fcfa59 100644
--- a/src/sfizz/Voice.cpp
+++ b/src/sfizz/Voice.cpp
@@ -5,6 +5,7 @@
 // If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
 
 #include "Voice.h"
+#include "Layer.h"
 #include "AudioBuffer.h"
 #include "Config.h"
 #include "Defaults.h"
@@ -198,7 +199,7 @@ struct Voice::Impl
     const NumericId<Voice> id_;
     StateListener* stateListener_ = nullptr;
 
-    Region* region_ { nullptr };
+    const Region* region_ { nullptr };
 
     State state_ { State::idle };
     bool noteIsOff_ { false };
@@ -362,18 +363,21 @@ Voice::Impl::Impl(int voiceNumber, Resources& resources)
     getSCurve();
 }
 
-bool Voice::startVoice(Region* region, int delay, const TriggerEvent& event) noexcept
+bool Voice::startVoice(Layer* layer, int delay, const TriggerEvent& event) noexcept
 {
     Impl& impl = *impl_;
     ASSERT(event.value >= 0.0f && event.value <= 1.0f);
 
-    impl.region_ = region;
+    Resources& resources = impl.resources_;
+
+    const Region& region = layer->getRegion();
+    impl.region_ = &region;
 
     impl.triggerEvent_ = event;
     if (impl.triggerEvent_.type == TriggerEventType::CC)
-        impl.triggerEvent_.number = region->pitchKeycenter;
+        impl.triggerEvent_.number = region.pitchKeycenter;
 
-    if (region->disabled()) {
+    if (region.disabled()) {
         impl.switchState(State::cleanMeUp);
         return false;
     }
@@ -384,33 +388,33 @@ bool Voice::startVoice(Region* region, int delay, const TriggerEvent& event) noe
     if (delay < 0)
         delay = 0;
 
-    if (region->isOscillator()) {
+    if (region.isOscillator()) {
         const WavetableMulti* wave = nullptr;
-        if (!region->isGenerator())
-            wave = impl.resources_.wavePool.getFileWave(region->sampleId->filename());
+        if (!region.isGenerator())
+            wave = resources.wavePool.getFileWave(region.sampleId->filename());
         else {
-            switch (hash(region->sampleId->filename())) {
+            switch (hash(region.sampleId->filename())) {
             default:
             case hash("*silence"):
                 break;
             case hash("*sine"):
-                wave = impl.resources_.wavePool.getWaveSin();
+                wave = resources.wavePool.getWaveSin();
                 break;
             case hash("*triangle"): // fallthrough
             case hash("*tri"):
-                wave = impl.resources_.wavePool.getWaveTriangle();
+                wave = resources.wavePool.getWaveTriangle();
                 break;
             case hash("*square"):
-                wave = impl.resources_.wavePool.getWaveSquare();
+                wave = resources.wavePool.getWaveSquare();
                 break;
             case hash("*saw"):
-                wave = impl.resources_.wavePool.getWaveSaw();
+                wave = resources.wavePool.getWaveSaw();
                 break;
             }
         }
-        const float phase = region->getPhase();
+        const float phase = region.getPhase();
         const int quality =
-            region->oscillatorQuality.value_or(Default::oscillatorQuality);
+            region.oscillatorQuality.value_or(Default::oscillatorQuality);
         for (WavetableOscillator& osc : impl.waveOscillators_) {
             osc.setWavetable(wave);
             osc.setPhase(phase);
@@ -418,61 +422,61 @@ bool Voice::startVoice(Region* region, int delay, const TriggerEvent& event) noe
         }
         impl.setupOscillatorUnison();
     } else {
-        impl.currentPromise_ = impl.resources_.filePool.getFilePromise(region->sampleId);
+        impl.currentPromise_ = resources.filePool.getFilePromise(region.sampleId);
         if (!impl.currentPromise_) {
             impl.switchState(State::cleanMeUp);
             return false;
         }
         impl.updateLoopInformation();
         impl.speedRatio_ = static_cast<float>(impl.currentPromise_->information.sampleRate / impl.sampleRate_);
-        impl.sourcePosition_ = region->getOffset(impl.resources_.filePool.getOversamplingFactor());
+        impl.sourcePosition_ = region.getOffset(resources.midiState, resources.filePool.getOversamplingFactor());
     }
 
     // do Scala retuning and reconvert the frequency into a 12TET key number
-    const float numberRetuned = impl.resources_.tuning.getKeyFractional12TET(impl.triggerEvent_.number);
+    const float numberRetuned = resources.tuning.getKeyFractional12TET(impl.triggerEvent_.number);
 
-    impl.pitchRatio_ = region->getBasePitchVariation(numberRetuned, impl.triggerEvent_.value);
+    impl.pitchRatio_ = region.getBasePitchVariation(numberRetuned, impl.triggerEvent_.value);
 
     // apply stretch tuning if set
-    if (impl.resources_.stretch)
-        impl.pitchRatio_ *= impl.resources_.stretch->getRatioForFractionalKey(numberRetuned);
+    if (resources.stretch)
+        impl.pitchRatio_ *= resources.stretch->getRatioForFractionalKey(numberRetuned);
 
-    impl.baseVolumedB_ = region->getBaseVolumedB(impl.triggerEvent_.number);
-    impl.baseGain_ = region->getBaseGain();
+    impl.baseVolumedB_ = region.getBaseVolumedB(resources.midiState, impl.triggerEvent_.number);
+    impl.baseGain_ = region.getBaseGain();
     if (impl.triggerEvent_.type != TriggerEventType::CC)
-        impl.baseGain_ *= region->getNoteGain(impl.triggerEvent_.number, impl.triggerEvent_.value);
+        impl.baseGain_ *= region.getNoteGain(impl.triggerEvent_.number, impl.triggerEvent_.value);
     impl.gainSmoother_.reset();
     impl.resetCrossfades();
 
-    for (unsigned i = 0; i < region->filters.size(); ++i) {
-        impl.filters_[i].setup(*region, i, impl.triggerEvent_.number, impl.triggerEvent_.value);
+    for (unsigned i = 0; i < region.filters.size(); ++i) {
+        impl.filters_[i].setup(region, i, impl.triggerEvent_.number, impl.triggerEvent_.value);
     }
 
-    for (unsigned i = 0; i < region->equalizers.size(); ++i) {
-        impl.equalizers_[i].setup(*region, i, impl.triggerEvent_.value);
+    for (unsigned i = 0; i < region.equalizers.size(); ++i) {
+        impl.equalizers_[i].setup(region, i, impl.triggerEvent_.value);
     }
 
     impl.triggerDelay_ = delay;
-    impl.initialDelay_ = delay + static_cast<int>(region->getDelay() * impl.sampleRate_);
-    impl.baseFrequency_ = impl.resources_.tuning.getFrequencyOfKey(impl.triggerEvent_.number);
-    impl.sampleSize_ = region->trueSampleEnd(impl.resources_.filePool.getOversamplingFactor()) - impl.sourcePosition_ - 1;
-    impl.bendStepFactor_ = centsFactor(region->bendStep);
-    impl.bendSmoother_.setSmoothing(region->bendSmooth, impl.sampleRate_);
-    impl.bendSmoother_.reset(centsFactor(region->getBendInCents(impl.resources_.midiState.getPitchBend())));
+    impl.initialDelay_ = delay + static_cast<int>(region.getDelay(resources.midiState) * impl.sampleRate_);
+    impl.baseFrequency_ = resources.tuning.getFrequencyOfKey(impl.triggerEvent_.number);
+    impl.sampleSize_ = region.trueSampleEnd(resources.filePool.getOversamplingFactor()) - impl.sourcePosition_ - 1;
+    impl.bendStepFactor_ = centsFactor(region.bendStep);
+    impl.bendSmoother_.setSmoothing(region.bendSmooth, impl.sampleRate_);
+    impl.bendSmoother_.reset(centsFactor(region.getBendInCents(resources.midiState.getPitchBend())));
 
-    impl.resources_.modMatrix.initVoice(impl.id_, region->getId(), impl.initialDelay_);
-    impl.saveModulationTargets(region);
+    resources.modMatrix.initVoice(impl.id_, region.getId(), impl.initialDelay_);
+    impl.saveModulationTargets(&region);
 
-    if (region->checkSustain) {
+    if (region.checkSustain) {
         const bool sustainPressed =
-            impl.resources_.midiState.getCCValue(region->sustainCC) >= region->sustainThreshold;
+            resources.midiState.getCCValue(region.sustainCC) >= region.sustainThreshold;
         impl.sustainState_ =
             sustainPressed ? Impl::SustainState::Sustaining : Impl::SustainState::Up;
     }
 
-    if (region->checkSostenuto) {
+    if (region.checkSostenuto) {
         const bool sostenutoPressed =
-            impl.resources_.midiState.getCCValue(region->sostenutoCC) >= region->sostenutoThreshold;
+            resources.midiState.getCCValue(region.sostenutoCC) >= region.sostenutoThreshold;
         impl.sostenutoState_ =
             sostenutoPressed ? Impl::SostenutoState::PreviouslyDown : Impl::SostenutoState::Up;
     }
diff --git a/src/sfizz/Voice.h b/src/sfizz/Voice.h
index ceaf3588..d6412424 100644
--- a/src/sfizz/Voice.h
+++ b/src/sfizz/Voice.h
@@ -18,6 +18,7 @@ namespace sfz {
 enum InterpolatorModel : int;
 class LFO;
 class FlexEnvelope;
+struct Layer;
 /**
  * @brief The SFZ voice are the polyphony holders. They get activated by the synth
  * and tasked to play a given region until the end, stopping on note-offs, off-groups
@@ -99,12 +100,12 @@ public:
     /**
      * @brief Start playing a region after a short delay for different triggers (note on, off, cc)
      *
-     * @param region
+     * @param layer
      * @param delay
      * @param evebt
      * @return bool
      */
-    bool startVoice(Region* region, int delay, const TriggerEvent& event) noexcept;
+    bool startVoice(Layer* layer, int delay, const TriggerEvent& event) noexcept;
 
     /**
      * @brief Get the sample quality determined by the active region.
diff --git a/tests/DirectRegionT.cpp b/tests/DirectRegionT.cpp
index 8f5bf6a6..f0d63c94 100644
--- a/tests/DirectRegionT.cpp
+++ b/tests/DirectRegionT.cpp
@@ -7,6 +7,7 @@
 #include "TestHelpers.h"
 #include "sfizz/MidiState.h"
 #include "sfizz/Region.h"
+#include "sfizz/Layer.h"
 #include "sfizz/SfzHelpers.h"
 #include "sfizz/modulations/ModId.h"
 #include "sfizz/modulations/ModKey.h"
@@ -18,8 +19,7 @@ using namespace sfz;
 
 TEST_CASE("[Direct Region Tests] amp_velcurve")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "amp_velcurve_6", "0.4" });
     REQUIRE(region.velocityPoints.back() == std::pair<uint8_t, float>(6, 0.4f));
     region.parseOpcode({ "amp_velcurve_127", "-1.0" });
@@ -33,87 +33,98 @@ TEST_CASE("[Direct Region Tests] amp_velcurve")
 TEST_CASE("[Direct Region Tests] Release and release key")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "lokey", "63" });
     region.parseOpcode({ "hikey", "65" });
     region.parseOpcode({ "sample", "*sine" });
-    region.delayedSustainReleases.reserve(config::delayedReleaseVoices);
     SECTION("Release key without sustain")
     {
         region.parseOpcode({ "trigger", "release_key" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 0.0f);
-        region.registerCC(64, 0.0f);
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
-        REQUIRE( region.registerNoteOff(63, 0.5f, 0.0f) );
+        layer.registerCC(64, 0.0f);
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( layer.registerNoteOff(63, 0.5f, 0.0f) );
     }
     SECTION("Release key with sustain")
     {
         region.parseOpcode({ "trigger", "release_key" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 1.0f);
-        region.registerCC(64, 1.0f);
-        REQUIRE( !region.registerCC(64, 1.0f) );
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
-        REQUIRE( region.registerNoteOff(63, 0.5f, 0.0f) );
+        layer.registerCC(64, 1.0f);
+        REQUIRE( !layer.registerCC(64, 1.0f) );
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( layer.registerNoteOff(63, 0.5f, 0.0f) );
     }
 
     SECTION("Release without sustain")
     {
         region.parseOpcode({ "trigger", "release" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 0.0f);
-        region.registerCC(64, 0.0f);
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
-        REQUIRE( region.registerNoteOff(63, 0.5f, 0.0f) );
+        layer.registerCC(64, 0.0f);
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( layer.registerNoteOff(63, 0.5f, 0.0f) );
     }
 
     SECTION("Release with sustain")
     {
         region.parseOpcode({ "trigger", "release" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 1.0f);
-        region.registerCC(64, 1.0f);
+        layer.registerCC(64, 1.0f);
         midiState.noteOnEvent(0, 63, 0.5f);
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
-        REQUIRE( !region.registerNoteOff(63, 0.5f, 0.0f) );
-        REQUIRE( region.delayedSustainReleases.size() == 1 );
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( !layer.registerNoteOff(63, 0.5f, 0.0f) );
+        REQUIRE( layer.delayedSustainReleases_.size() == 1 );
         std::vector<std::pair<int, float>> expected = {
             { 63, 0.5f }
         };
-        REQUIRE( region.delayedSustainReleases == expected );
+        REQUIRE( layer.delayedSustainReleases_ == expected );
     }
 
     SECTION("Release with sustain and 2 notes")
     {
         region.parseOpcode({ "trigger", "release" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 1.0f);
-        region.registerCC(64, 1.0f);
+        layer.registerCC(64, 1.0f);
         midiState.noteOnEvent(0, 63, 0.5f);
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
         midiState.noteOnEvent(0, 64, 0.6f);
-        REQUIRE( !region.registerNoteOn(64, 0.6f, 0.0f) );
-        REQUIRE( !region.registerNoteOff(63, 0.0f, 0.0f) );
-        REQUIRE( !region.registerNoteOff(64, 0.2f, 0.0f) );
-        REQUIRE( region.delayedSustainReleases.size() == 2 );
+        REQUIRE( !layer.registerNoteOn(64, 0.6f, 0.0f) );
+        REQUIRE( !layer.registerNoteOff(63, 0.0f, 0.0f) );
+        REQUIRE( !layer.registerNoteOff(64, 0.2f, 0.0f) );
+        REQUIRE( layer.delayedSustainReleases_.size() == 2 );
         std::vector<std::pair<int, float>> expected = {
             { 63, 0.5f },
             { 64, 0.6f }
         };
-        REQUIRE( region.delayedSustainReleases == expected );
+        REQUIRE( layer.delayedSustainReleases_ == expected );
     }
 
     SECTION("Release with sustain and 2 notes but 1 outside")
     {
         region.parseOpcode({ "trigger", "release" });
+        Layer layer { &region, midiState };
+        layer.delayedSustainReleases_.reserve(config::delayedReleaseVoices);
         midiState.ccEvent(0, 64, 1.0f);
-        region.registerCC(64, 1.0f);
+        layer.registerCC(64, 1.0f);
         midiState.noteOnEvent(0, 63, 0.5f);
-        REQUIRE( !region.registerNoteOn(63, 0.5f, 0.0f) );
+        REQUIRE( !layer.registerNoteOn(63, 0.5f, 0.0f) );
         midiState.noteOnEvent(0, 66, 0.6f);
-        REQUIRE( !region.registerNoteOn(66, 0.6f, 0.0f) );
-        REQUIRE( !region.registerNoteOff(63, 0.0f, 0.0f) );
-        REQUIRE( !region.registerNoteOff(66, 0.2f, 0.0f) );
-        REQUIRE( region.delayedSustainReleases.size() == 1 );
+        REQUIRE( !layer.registerNoteOn(66, 0.6f, 0.0f) );
+        REQUIRE( !layer.registerNoteOff(63, 0.0f, 0.0f) );
+        REQUIRE( !layer.registerNoteOff(66, 0.2f, 0.0f) );
+        REQUIRE( layer.delayedSustainReleases_.size() == 1 );
         std::vector<std::pair<int, float>> expected = {
             { 63, 0.5f }
         };
-        REQUIRE( region.delayedSustainReleases == expected );
+        REQUIRE( layer.delayedSustainReleases_ == expected );
     }
 }
diff --git a/tests/RegionActivationT.cpp b/tests/RegionActivationT.cpp
index 13f6b660..cca98f99 100644
--- a/tests/RegionActivationT.cpp
+++ b/tests/RegionActivationT.cpp
@@ -4,6 +4,7 @@
 // license. You should have receive a LICENSE.md file along with the code.
 // If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
 
+#include "sfizz/Layer.h"
 #include "sfizz/Region.h"
 #include "sfizz/Synth.h"
 #include "sfizz/SfzHelpers.h"
@@ -14,33 +15,35 @@ using namespace sfz::literals;
 TEST_CASE("Region activation", "Region tests")
 {
     sfz::MidiState midiState;
-    sfz::Region region { 0, midiState };
+    sfz::Region region { 0 };
 
     region.parseOpcode({ "sample", "*sine" });
     SECTION("Basic state")
     {
-        region.registerCC(4, 0_norm);
-        REQUIRE(region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerCC(4, 0_norm);
+        REQUIRE(layer.isSwitchedOn());
     }
 
     SECTION("Single CC range")
     {
         region.parseOpcode({ "locc4", "56" });
         region.parseOpcode({ "hicc4", "59" });
-        region.registerCC(4, 0_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(4, 57_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 56_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 59_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 43_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(4, 65_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(6, 57_norm);
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerCC(4, 0_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(4, 57_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 56_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 59_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 43_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(4, 65_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(6, 57_norm);
+        REQUIRE(!layer.isSwitchedOn());
     }
 
     SECTION("Multiple CC ranges")
@@ -49,69 +52,73 @@ TEST_CASE("Region activation", "Region tests")
         region.parseOpcode({ "hicc4", "59" });
         region.parseOpcode({ "locc54", "18" });
         region.parseOpcode({ "hicc54", "27" });
-        region.registerCC(4, 0_norm);
-        region.registerCC(54, 0_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(4, 57_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(54, 19_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(54, 17_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(54, 27_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 56_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 59_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(54, 2_norm);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerCC(54, 26_norm);
-        REQUIRE(region.isSwitchedOn());
-        region.registerCC(4, 65_norm);
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerCC(4, 0_norm);
+        layer.registerCC(54, 0_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(4, 57_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(54, 19_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(54, 17_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(54, 27_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 56_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 59_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(54, 2_norm);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerCC(54, 26_norm);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerCC(4, 65_norm);
+        REQUIRE(!layer.isSwitchedOn());
     }
 
     SECTION("Bend ranges")
     {
         region.parseOpcode({ "lobend", "56" });
         region.parseOpcode({ "hibend", "243" });
-        region.registerPitchWheel(0);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerPitchWheel(sfz::normalizeBend(56));
-        REQUIRE(region.isSwitchedOn());
-        region.registerPitchWheel(sfz::normalizeBend(243));
-        REQUIRE(region.isSwitchedOn());
-        region.registerPitchWheel(sfz::normalizeBend(245));
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerPitchWheel(0);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerPitchWheel(sfz::normalizeBend(56));
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerPitchWheel(sfz::normalizeBend(243));
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerPitchWheel(sfz::normalizeBend(245));
+        REQUIRE(!layer.isSwitchedOn());
     }
 
     SECTION("Aftertouch ranges")
     {
         region.parseOpcode({ "lochanaft", "56" });
         region.parseOpcode({ "hichanaft", "68" });
-        region.registerAftertouch(sfz::normalize7Bits(0));
-        REQUIRE(!region.isSwitchedOn());
-        region.registerAftertouch(sfz::normalize7Bits(56));
-        REQUIRE(region.isSwitchedOn());
-        region.registerAftertouch(sfz::normalize7Bits(68));
-        REQUIRE(region.isSwitchedOn());
-        region.registerAftertouch(sfz::normalize7Bits(98));
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerAftertouch(sfz::normalize7Bits(0));
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerAftertouch(sfz::normalize7Bits(56));
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerAftertouch(sfz::normalize7Bits(68));
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerAftertouch(sfz::normalize7Bits(98));
+        REQUIRE(!layer.isSwitchedOn());
     }
 
     SECTION("BPM ranges")
     {
         region.parseOpcode({ "lobpm", "56" });
         region.parseOpcode({ "hibpm", "68" });
-        region.registerTempo(2.0f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerTempo(0.90f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerTempo(1.01f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerTempo(1.1f);
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        layer.registerTempo(2.0f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerTempo(0.90f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerTempo(1.01f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerTempo(1.1f);
+        REQUIRE(!layer.isSwitchedOn());
     }
 
     SECTION("Sequences: length 2, default position")
@@ -119,61 +126,64 @@ TEST_CASE("Region activation", "Region tests")
         region.parseOpcode({ "seq_length", "2" });
         region.parseOpcode({ "seq_position", "1" });
         region.parseOpcode({ "key", "40" });
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
     }
     SECTION("Sequences: length 2, position 2")
     {
         region.parseOpcode({ "seq_length", "2" });
         region.parseOpcode({ "seq_position", "2" });
         region.parseOpcode({ "key", "40" });
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
     }
     SECTION("Sequences: length 3, position 2")
     {
         region.parseOpcode({ "seq_length", "3" });
         region.parseOpcode({ "seq_position", "2" });
         region.parseOpcode({ "key", "40" });
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOn(40, 64_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
-        region.registerNoteOff(40, 0_norm, 0.5f);
-        REQUIRE(!region.isSwitchedOn());
+        sfz::Layer layer { &region, midiState };
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOn(40, 64_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
+        layer.registerNoteOff(40, 0_norm, 0.5f);
+        REQUIRE(!layer.isSwitchedOn());
     }
 }
 
@@ -341,10 +351,10 @@ TEST_CASE("[Keyswitches] sw_default")
         <region> sw_last=40 key=54 sample=*sine
     )");
     REQUIRE( synth.getNumRegions() == 4 );
-    REQUIRE( !synth.getRegionView(0)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(1)->isSwitchedOn() );
-    REQUIRE( !synth.getRegionView(2)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(3)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(0)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(1)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(2)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(3)->isSwitchedOn() );
 }
 
 TEST_CASE("[Keyswitches] sw_default and playing with switches")
@@ -358,22 +368,22 @@ TEST_CASE("[Keyswitches] sw_default and playing with switches")
         <region> sw_last=40 key=54 sample=*sine
     )");
     REQUIRE( synth.getNumRegions() == 4 );
-    REQUIRE( !synth.getRegionView(0)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(1)->isSwitchedOn() );
-    REQUIRE( !synth.getRegionView(2)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(3)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(0)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(1)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(2)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(3)->isSwitchedOn() );
     synth.noteOn(0, 41, 64);
     synth.noteOff(0, 41, 0);
-    REQUIRE( synth.getRegionView(0)->isSwitchedOn() );
-    REQUIRE( !synth.getRegionView(1)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(2)->isSwitchedOn() );
-    REQUIRE( !synth.getRegionView(3)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(0)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(1)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(2)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(3)->isSwitchedOn() );
     synth.noteOn(0, 40, 64);
     synth.noteOff(0, 40, 64);
-    REQUIRE( !synth.getRegionView(0)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(1)->isSwitchedOn() );
-    REQUIRE( !synth.getRegionView(2)->isSwitchedOn() );
-    REQUIRE( synth.getRegionView(3)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(0)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(1)->isSwitchedOn() );
+    REQUIRE( !synth.getLayerView(2)->isSwitchedOn() );
+    REQUIRE( synth.getLayerView(3)->isSwitchedOn() );
 }
 
 TEST_CASE("[Keyswitches] sw_previous in range")
@@ -385,21 +395,21 @@ TEST_CASE("[Keyswitches] sw_previous in range")
     // Note: sforzando seems to activate by default if sw_previous is indeed 60,
     // but not any other value. As it does not seem really useful at this point
     // the test assumes that sw_previous regions are disabled by default
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 51, 64);
     REQUIRE(synth.getNumActiveVoices() == 0);
     synth.noteOn(0, 60, 64);
     REQUIRE(synth.getNumActiveVoices() == 0);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 51, 64);
     REQUIRE(synth.getNumActiveVoices() == 1);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 60, 64);
     REQUIRE(synth.getNumActiveVoices() == 1);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 60, 64);
     REQUIRE(synth.getNumActiveVoices() == 2);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] sw_previous out of range")
@@ -409,20 +419,20 @@ TEST_CASE("[Keyswitches] sw_previous out of range")
     synth.loadSfzString(fs::current_path() / "tests/TestFiles/sw_previous.sfz", R"(
         <region> sample=*saw sw_previous=60 lokey=50 hikey=55
     )");
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 51, 64);
     REQUIRE(synth.getNumActiveVoices() == 0);
     synth.noteOn(0, 60, 64);
     REQUIRE(synth.getNumActiveVoices() == 0);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 51, 64);
     REQUIRE(synth.getNumActiveVoices() == 1);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 60, 64);
     REQUIRE(synth.getNumActiveVoices() == 1);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
     synth.noteOn(0, 61, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] sw_lolast and sw_hilast")
@@ -432,29 +442,29 @@ TEST_CASE("[Keyswitches] sw_lolast and sw_hilast")
         <region> sw_lolast=57 sw_hilast=59 key=70 sample=*saw
         <region> sw_lolast=60 sw_hilast=62 key=72 sample=*sine
     )");
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 51, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 57, 64);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 60, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 58, 64);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 61, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 59, 64);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 62, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] sw_lolast and sw_hilast with sw_last")
@@ -464,26 +474,26 @@ TEST_CASE("[Keyswitches] sw_lolast and sw_hilast with sw_last")
         <region> sw_last=40 sw_lolast=57 sw_hilast=59 key=70 sample=*saw
         <region> sw_lolast=60 sw_hilast=62 sw_last=41 key=72 sample=*sine
     )");
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 40, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 41, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 57, 64);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 41, 64);
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 60, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
     synth.noteOn(0, 40, 64);
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] sw_lolast and sw_hilast with sw_default")
@@ -494,8 +504,8 @@ TEST_CASE("[Keyswitches] sw_lolast and sw_hilast with sw_default")
         <region> sw_lolast=57 sw_hilast=59 key=70 sample=*saw
         <region> sw_lolast=60 sw_hilast=62 key=72 sample=*sine
     )");
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] Multiple sw_default")
@@ -509,10 +519,10 @@ TEST_CASE("[Keyswitches] Multiple sw_default")
         <master> sw_default=59
         <region> sw_last=62 key=73 sample=*saw
     )");
-    REQUIRE(!synth.getRegionView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(0)->isSwitchedOn());
     // Only the last one is taken into account
-    REQUIRE(synth.getRegionView(1)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(2)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(1)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(2)->isSwitchedOn());
 }
 
 TEST_CASE("[Keyswitches] Multiple sw_default, in region")
@@ -523,7 +533,7 @@ TEST_CASE("[Keyswitches] Multiple sw_default, in region")
         <region> sw_last=58 key=70 sample=*saw
         <region> sw_default=58 sw_last=59 key=72 sample=*saw
     )");
-    REQUIRE(synth.getRegionView(0)->isSwitchedOn());
-    REQUIRE(!synth.getRegionView(1)->isSwitchedOn());
+    REQUIRE(synth.getLayerView(0)->isSwitchedOn());
+    REQUIRE(!synth.getLayerView(1)->isSwitchedOn());
 }
 
diff --git a/tests/RegionTriggersT.cpp b/tests/RegionTriggersT.cpp
index 6817acb5..30b1cad5 100644
--- a/tests/RegionTriggersT.cpp
+++ b/tests/RegionTriggersT.cpp
@@ -7,6 +7,7 @@
 #include "TestHelpers.h"
 #include "sfizz/Synth.h"
 #include "sfizz/Region.h"
+#include "sfizz/Layer.h"
 #include "sfizz/SfzHelpers.h"
 #include "catch2/catch.hpp"
 using namespace Catch::literals;
@@ -16,50 +17,54 @@ using namespace sfz;
 TEST_CASE("Basic triggers", "Region triggers")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
 
     region.parseOpcode({ "sample", "*sine" });
     SECTION("key")
     {
         region.parseOpcode({ "key", "40" });
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(40, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(41, 64_norm, 0.5f));
-        REQUIRE(!region.registerCC(63, 64_norm));
+        Layer layer { &region, midiState };
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerCC(63, 64_norm));
     }
     SECTION("lokey and hikey")
     {
         region.parseOpcode({ "lokey", "40" });
         region.parseOpcode({ "hikey", "42" });
-        REQUIRE(!region.registerNoteOn(39, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(40, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOn(41, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOn(42, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(43, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(42, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(42, 64_norm, 0.5f));
-        REQUIRE(!region.registerCC(63, 64_norm));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerNoteOn(39, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(40, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(42, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(43, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(42, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(42, 64_norm, 0.5f));
+        REQUIRE(!layer.registerCC(63, 64_norm));
     }
     SECTION("key and release trigger")
     {
         region.parseOpcode({ "key", "40" });
         region.parseOpcode({ "trigger", "release" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOff(40, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(41, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(41, 64_norm, 0.5f));
-        REQUIRE(!region.registerCC(63, 64_norm));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOff(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerCC(63, 64_norm));
     }
     SECTION("key and release_key trigger")
     {
         region.parseOpcode({ "key", "40" });
         region.parseOpcode({ "trigger", "release_key" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOff(40, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(41, 64_norm, 0.5f));
-        REQUIRE(!region.registerNoteOff(41, 64_norm, 0.5f));
-        REQUIRE(!region.registerCC(63, 64_norm));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOff(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOff(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerCC(63, 64_norm));
     }
     // TODO: first and legato triggers
     SECTION("lovel and hivel")
@@ -67,11 +72,12 @@ TEST_CASE("Basic triggers", "Region triggers")
         region.parseOpcode({ "key", "40" });
         region.parseOpcode({ "lovel", "60" });
         region.parseOpcode({ "hivel", "70" });
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.5f));
-        REQUIRE(region.registerNoteOn(40, 60_norm, 0.5f));
-        REQUIRE(region.registerNoteOn(40, 70_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(41, 71_norm, 0.5f));
-        REQUIRE(!region.registerNoteOn(41, 59_norm, 0.5f));
+        Layer layer { &region, midiState };
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(40, 60_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(40, 70_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 71_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 59_norm, 0.5f));
     }
 
     SECTION("lorand and hirand")
@@ -79,54 +85,63 @@ TEST_CASE("Basic triggers", "Region triggers")
         region.parseOpcode({ "key", "40" });
         region.parseOpcode({ "lorand", "0.35" });
         region.parseOpcode({ "hirand", "0.40" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.34f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.35f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.36f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.37f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.38f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.39f));
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.40f));
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.41f));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.34f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.35f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.36f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.37f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.38f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.39f));
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.40f));
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.41f));
     }
 
     SECTION("lorand and hirand on 1.0f")
     {
         region.parseOpcode({ "key", "40" });
         region.parseOpcode({ "lorand", "0.35" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.34f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.35f));
-        REQUIRE(region.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.34f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.35f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 1.0f));
     }
 
     SECTION("Disable key trigger")
     {
         region.parseOpcode({ "key", "40" });
-        REQUIRE(region.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer1 { &region, midiState };
+        REQUIRE(layer1.registerNoteOn(40, 64_norm, 1.0f));
         region.parseOpcode({ "hikey", "-1" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer2 { &region, midiState };
+        REQUIRE(!layer2.registerNoteOn(40, 64_norm, 1.0f));
         region.parseOpcode({ "hikey", "40" });
-        REQUIRE(region.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer3 { &region, midiState };
+        REQUIRE(layer3.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer4 { &region, midiState };
         region.parseOpcode({ "key", "-1" });
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 1.0f));
+        REQUIRE(!layer4.registerNoteOn(40, 64_norm, 1.0f));
+        Layer layer5 { &region, midiState };
         region.parseOpcode({ "key", "40" });
-        REQUIRE(region.registerNoteOn(40, 64_norm, 1.0f));
+        REQUIRE(layer5.registerNoteOn(40, 64_norm, 1.0f));
     }
 
     SECTION("on_loccN, on_hiccN")
     {
         region.parseOpcode({ "on_locc47", "64" });
         region.parseOpcode({ "on_hicc47", "68" });
-        REQUIRE(!region.registerCC(47, 63_norm));
-        REQUIRE(region.registerCC(47, 64_norm));
-        REQUIRE(region.registerCC(47, 65_norm));
+        Layer layer1 { &region, midiState };
+        REQUIRE(!layer1.registerCC(47, 63_norm));
+        REQUIRE(layer1.registerCC(47, 64_norm));
+        REQUIRE(layer1.registerCC(47, 65_norm));
         region.parseOpcode({ "hikey", "-1" });
-        REQUIRE(region.registerCC(47, 64_norm));
-        REQUIRE(region.registerCC(47, 65_norm));
-        REQUIRE(region.registerCC(47, 66_norm));
-        REQUIRE(region.registerCC(47, 67_norm));
-        REQUIRE(region.registerCC(47, 68_norm));
-        REQUIRE(!region.registerCC(47, 69_norm));
-        REQUIRE(!region.registerCC(40, 64_norm));
+        Layer layer2 { &region, midiState };
+        REQUIRE(layer2.registerCC(47, 64_norm));
+        REQUIRE(layer2.registerCC(47, 65_norm));
+        REQUIRE(layer2.registerCC(47, 66_norm));
+        REQUIRE(layer2.registerCC(47, 67_norm));
+        REQUIRE(layer2.registerCC(47, 68_norm));
+        REQUIRE(!layer2.registerCC(47, 69_norm));
+        REQUIRE(!layer2.registerCC(40, 64_norm));
     }
 
     SECTION("on_loccN does not disable key triggering")
@@ -134,10 +149,11 @@ TEST_CASE("Basic triggers", "Region triggers")
         region.parseOpcode({ "sample", "*sine" });
         region.parseOpcode({ "on_locc1", "127" });
         region.parseOpcode({ "on_hicc1", "127" });
-        REQUIRE(!region.registerCC(1, 126_norm));
-        REQUIRE(!region.registerCC(2, 127_norm));
-        REQUIRE(region.registerCC(1, 127_norm));
-        REQUIRE(region.registerNoteOn(64, 127_norm, 0.5f));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerCC(1, 126_norm));
+        REQUIRE(!layer.registerCC(2, 127_norm));
+        REQUIRE(layer.registerCC(1, 127_norm));
+        REQUIRE(layer.registerNoteOn(64, 127_norm, 0.5f));
     }
 
     SECTION("on_loccN does not disable key triggering, but adding key=-1 does")
@@ -146,9 +162,10 @@ TEST_CASE("Basic triggers", "Region triggers")
         region.parseOpcode({ "on_locc1", "127" });
         region.parseOpcode({ "on_hicc1", "127" });
         region.parseOpcode({ "key", "-1" });
-        REQUIRE(!region.registerCC(1, 126_norm));
-        REQUIRE(region.registerCC(1, 127_norm));
-        REQUIRE(!region.registerNoteOn(64, 127_norm, 0.5f));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerCC(1, 126_norm));
+        REQUIRE(layer.registerCC(1, 127_norm));
+        REQUIRE(!layer.registerNoteOn(64, 127_norm, 0.5f));
     }
 
     SECTION("on_loccN does not disable key triggering, but adding hikey=-1 does")
@@ -157,33 +174,35 @@ TEST_CASE("Basic triggers", "Region triggers")
         region.parseOpcode({ "on_locc1", "127" });
         region.parseOpcode({ "on_hicc1", "127" });
         region.parseOpcode({ "hikey", "-1" });
-        REQUIRE(!region.registerCC(1, 126_norm));
-        REQUIRE(!region.registerCC(2, 127_norm));
-        REQUIRE(region.registerCC(1, 127_norm));
-        REQUIRE(!region.registerNoteOn(64, 127_norm, 0.5f));
+        Layer layer { &region, midiState };
+        REQUIRE(!layer.registerCC(1, 126_norm));
+        REQUIRE(!layer.registerCC(2, 127_norm));
+        REQUIRE(layer.registerCC(1, 127_norm));
+        REQUIRE(!layer.registerNoteOn(64, 127_norm, 0.5f));
     }
 }
 
 TEST_CASE("Legato triggers", "Region triggers")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     SECTION("First note playing")
     {
         region.parseOpcode({ "lokey", "40" });
         region.parseOpcode({ "hikey", "50" });
         region.parseOpcode({ "trigger", "first" });
+        Layer layer { &region, midiState };
         midiState.noteOnEvent(0, 40, 64_norm);
-        REQUIRE(region.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(40, 64_norm, 0.5f));
         midiState.noteOnEvent(0, 41, 64_norm);
-        REQUIRE(!region.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(41, 64_norm, 0.5f));
         midiState.noteOffEvent(0, 40, 0_norm);
-        region.registerNoteOff(40, 0_norm, 0.5f);
+        layer.registerNoteOff(40, 0_norm, 0.5f);
         midiState.noteOffEvent(0, 41, 0_norm);
-        region.registerNoteOff(41, 0_norm, 0.5f);
+        layer.registerNoteOff(41, 0_norm, 0.5f);
         midiState.noteOnEvent(0, 42, 64_norm);
-        REQUIRE(region.registerNoteOn(42, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(42, 64_norm, 0.5f));
     }
 
     SECTION("Second note playing")
@@ -191,16 +210,17 @@ TEST_CASE("Legato triggers", "Region triggers")
         region.parseOpcode({ "lokey", "40" });
         region.parseOpcode({ "hikey", "50" });
         region.parseOpcode({ "trigger", "legato" });
+        Layer layer { &region, midiState };
         midiState.noteOnEvent(0, 40, 64_norm);
-        REQUIRE(!region.registerNoteOn(40, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(40, 64_norm, 0.5f));
         midiState.noteOnEvent(0, 41, 64_norm);
-        REQUIRE(region.registerNoteOn(41, 64_norm, 0.5f));
+        REQUIRE(layer.registerNoteOn(41, 64_norm, 0.5f));
         midiState.noteOffEvent(0, 40, 64_norm);
-        region.registerNoteOff(40, 0_norm, 0.5f);
+        layer.registerNoteOff(40, 0_norm, 0.5f);
         midiState.noteOffEvent(0, 41, 64_norm);
-        region.registerNoteOff(41, 0_norm, 0.5f);
+        layer.registerNoteOff(41, 0_norm, 0.5f);
         midiState.noteOnEvent(0, 42, 64_norm);
-        REQUIRE(!region.registerNoteOn(42, 64_norm, 0.5f));
+        REQUIRE(!layer.registerNoteOn(42, 64_norm, 0.5f));
     }
 }
 
diff --git a/tests/RegionValueComputationsT.cpp b/tests/RegionValueComputationsT.cpp
index f3b1abca..c7516830 100644
--- a/tests/RegionValueComputationsT.cpp
+++ b/tests/RegionValueComputationsT.cpp
@@ -18,8 +18,7 @@ constexpr int numRandomTests { 64 };
 
 TEST_CASE("[Region] Crossfade in on key")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_lokey", "1" });
     region.parseOpcode({ "xfin_hikey", "3" });
@@ -30,8 +29,7 @@ TEST_CASE("[Region] Crossfade in on key")
 
 TEST_CASE("[Region] Crossfade in on key - 2")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_lokey", "1" });
     region.parseOpcode({ "xfin_hikey", "5" });
@@ -45,8 +43,7 @@ TEST_CASE("[Region] Crossfade in on key - 2")
 
 TEST_CASE("[Region] Crossfade in on key - gain")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_lokey", "1" });
     region.parseOpcode({ "xfin_hikey", "5" });
@@ -60,8 +57,7 @@ TEST_CASE("[Region] Crossfade in on key - gain")
 
 TEST_CASE("[Region] Crossfade out on key")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_lokey", "51" });
     region.parseOpcode({ "xfout_hikey", "55" });
@@ -76,8 +72,7 @@ TEST_CASE("[Region] Crossfade out on key")
 
 TEST_CASE("[Region] Crossfade out on key - gain")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_lokey", "51" });
     region.parseOpcode({ "xfout_hikey", "55" });
@@ -93,8 +88,7 @@ TEST_CASE("[Region] Crossfade out on key - gain")
 
 TEST_CASE("[Region] Crossfade in on velocity")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_lovel", "20" });
     region.parseOpcode({ "xfin_hivel", "24" });
@@ -110,8 +104,7 @@ TEST_CASE("[Region] Crossfade in on velocity")
 
 TEST_CASE("[Region] Crossfade in on vel - gain")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_lovel", "20" });
     region.parseOpcode({ "xfin_hivel", "24" });
@@ -128,8 +121,7 @@ TEST_CASE("[Region] Crossfade in on vel - gain")
 
 TEST_CASE("[Region] Crossfade out on vel")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_lovel", "51" });
     region.parseOpcode({ "xfout_hivel", "55" });
@@ -145,8 +137,7 @@ TEST_CASE("[Region] Crossfade out on vel")
 
 TEST_CASE("[Region] Crossfade out on vel - gain")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_lovel", "51" });
     region.parseOpcode({ "xfout_hivel", "55" });
@@ -164,104 +155,103 @@ TEST_CASE("[Region] Crossfade out on vel - gain")
 TEST_CASE("[Region] Crossfade in on CC")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_locc24", "20" });
     region.parseOpcode({ "xfin_hicc24", "24" });
     region.parseOpcode({ "amp_veltrack", "0" });
     midiState.ccEvent(0, 24, 19_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 20_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 21_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.5_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.5_a);
     midiState.ccEvent(0, 24, 22_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.70711_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.70711_a);
     midiState.ccEvent(0, 24, 23_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.86603_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.86603_a);
     midiState.ccEvent(0, 24, 24_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 25_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
 }
 
 TEST_CASE("[Region] Crossfade in on CC - gain")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfin_locc24", "20" });
     region.parseOpcode({ "xfin_hicc24", "24" });
     region.parseOpcode({ "amp_veltrack", "0" });
     region.parseOpcode({ "xf_cccurve", "gain" });
     midiState.ccEvent(0, 24, 19_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 20_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 21_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.25_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.25_a);
     midiState.ccEvent(0, 24, 22_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.5_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.5_a);
     midiState.ccEvent(0, 24, 23_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.75_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.75_a);
     midiState.ccEvent(0, 24, 24_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 25_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
 }
 TEST_CASE("[Region] Crossfade out on CC")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_locc24", "20" });
     region.parseOpcode({ "xfout_hicc24", "24" });
     region.parseOpcode({ "amp_veltrack", "0" });
     midiState.ccEvent(0, 24, 19_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 20_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 21_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.86603_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.86603_a);
     midiState.ccEvent(0, 24, 22_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.70711_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.70711_a);
     midiState.ccEvent(0, 24, 23_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.5_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.5_a);
     midiState.ccEvent(0, 24, 24_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 25_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
 }
 
 TEST_CASE("[Region] Crossfade out on CC - gain")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "xfout_locc24", "20" });
     region.parseOpcode({ "xfout_hicc24", "24" });
     region.parseOpcode({ "amp_veltrack", "0" });
     region.parseOpcode({ "xf_cccurve", "gain" });
     midiState.ccEvent(0, 24, 19_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 20_norm);
-    REQUIRE(region.getCrossfadeGain() == 1.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 1.0_a);
     midiState.ccEvent(0, 24, 21_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.75_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.75_a);
     midiState.ccEvent(0, 24, 22_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.5_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.5_a);
     midiState.ccEvent(0, 24, 23_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.25_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.25_a);
     midiState.ccEvent(0, 24, 24_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
     midiState.ccEvent(0, 24, 25_norm);
-    REQUIRE(region.getCrossfadeGain() == 0.0_a);
+    REQUIRE(region.getCrossfadeGain(midiState) == 0.0_a);
 }
 
 TEST_CASE("[Region] Velocity bug for extreme values - veltrack at 0")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "amp_veltrack", "0" });
     REQUIRE(region.getNoteGain(64, 127_norm) == 1.0_a);
@@ -271,8 +261,7 @@ TEST_CASE("[Region] Velocity bug for extreme values - veltrack at 0")
 
 TEST_CASE("[Region] Velocity bug for extreme values - positive veltrack")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "amp_veltrack", "100" });
     REQUIRE(region.getNoteGain(64, 127_norm) == 1.0_a);
@@ -281,8 +270,7 @@ TEST_CASE("[Region] Velocity bug for extreme values - positive veltrack")
 
 TEST_CASE("[Region] Velocity bug for extreme values - negative veltrack")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "amp_veltrack", "-100" });
     REQUIRE(region.getNoteGain(64, 127_norm) == Approx(0.0).margin(0.0001));
@@ -293,35 +281,35 @@ TEST_CASE("[Region] rt_decay")
 {
     MidiState midiState;
     midiState.setSampleRate(1000);
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "trigger", "release" });
     region.parseOpcode({ "rt_decay", "10" });
     midiState.noteOnEvent(0, 64, 64_norm);
     midiState.advanceTime(100);
-    REQUIRE( region.getBaseVolumedB(64) == Approx(Default::volume - 1.0f).margin(0.1) );
+    REQUIRE( region.getBaseVolumedB(midiState, 64) == Approx(Default::volume - 1.0f).margin(0.1) );
     region.parseOpcode({ "rt_decay", "20" });
     midiState.noteOnEvent(0, 64, 64_norm);
     midiState.advanceTime(100);
-    REQUIRE( region.getBaseVolumedB(64) == Approx(Default::volume - 2.0f).margin(0.1) );
+    REQUIRE( region.getBaseVolumedB(midiState, 64) == Approx(Default::volume - 2.0f).margin(0.1) );
     region.parseOpcode({ "trigger", "attack" });
     midiState.noteOnEvent(0, 64, 64_norm);
     midiState.advanceTime(100);
-    REQUIRE( region.getBaseVolumedB(64) == Approx(Default::volume).margin(0.1) );
+    REQUIRE( region.getBaseVolumedB(midiState, 64) == Approx(Default::volume).margin(0.1) );
 }
 
 TEST_CASE("[Region] Base delay")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
     region.parseOpcode({ "sample", "*sine" });
     region.parseOpcode({ "delay", "10" });
-    REQUIRE( region.getDelay() == 10.0f );
+    REQUIRE( region.getDelay(midiState) == 10.0f );
     region.parseOpcode({ "delay_random", "10" });
     Random::randomGenerator.seed(42);
     for (int i = 0; i < numRandomTests; ++i)
     {
-        auto delay = region.getDelay();
+        auto delay = region.getDelay(midiState);
         REQUIRE( (delay >= 10.0 && delay <= 20.0) );
     }
 }
@@ -329,25 +317,24 @@ TEST_CASE("[Region] Base delay")
 TEST_CASE("[Region] Offsets with CCs")
 {
     MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
 
     region.parseOpcode({ "offset_cc4", "255" });
     region.parseOpcode({ "offset", "10" });
-    REQUIRE( region.getOffset() == 10 );
+    REQUIRE( region.getOffset(midiState) == 10 );
     midiState.ccEvent(0, 4, 127_norm);
-    REQUIRE( region.getOffset() == 265 );
+    REQUIRE( region.getOffset(midiState) == 265 );
     midiState.ccEvent(0, 4, 100_norm);
-    REQUIRE( region.getOffset() == 210 );
+    REQUIRE( region.getOffset(midiState) == 210 );
     midiState.ccEvent(0, 4, 10_norm);
-    REQUIRE( region.getOffset() == 30 );
+    REQUIRE( region.getOffset(midiState) == 30 );
     midiState.ccEvent(0, 4, 0);
-    REQUIRE( region.getOffset() == 10 );
+    REQUIRE( region.getOffset(midiState) == 10 );
 }
 
 TEST_CASE("[Region] Pitch variation with veltrack")
 {
-    MidiState midiState;
-    Region region { 0, midiState };
+    Region region { 0 };
 
     REQUIRE(region.getBasePitchVariation(60.0, 0_norm) == 1.0);
     REQUIRE(region.getBasePitchVariation(60.0, 64_norm) == 1.0);
@@ -357,4 +344,3 @@ TEST_CASE("[Region] Pitch variation with veltrack")
     REQUIRE(region.getBasePitchVariation(60.0, 64_norm) == Approx(centsFactor(600.0)).margin(0.01f));
     REQUIRE(region.getBasePitchVariation(60.0, 127_norm) == Approx(centsFactor(1200.0)).margin(0.01f));
 }
-
diff --git a/tests/SynthT.cpp b/tests/SynthT.cpp
index cb97a0f7..5ae2cb51 100644
--- a/tests/SynthT.cpp
+++ b/tests/SynthT.cpp
@@ -5,13 +5,15 @@
 // If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
 
 #include "sfizz/Synth.h"
+#include "sfizz/Region.h"
+#include "sfizz/Layer.h"
 #include "sfizz/SisterVoiceRing.h"
 #include "sfizz/SfzHelpers.h"
 #include "sfizz/utility/NumericId.h"
 #include "BitArray.h"
 #include "TestHelpers.h"
-#include <algorithm>
 #include "catch2/catch.hpp"
+#include <algorithm>
 using namespace Catch::literals;
 using namespace sfz::literals;
 
@@ -1111,7 +1113,7 @@ TEST_CASE("[Synth] Release (Multiple notes, release, cleared the delayed voices
     sortAll(requiredVelocities, actualVelocities);
     REQUIRE( requiredVelocities == actualVelocities );
 
-    REQUIRE( synth.getRegionView(1)->delayedSustainReleases.empty() );
+    REQUIRE( synth.getLayerView(1)->delayedSustainReleases_.empty() );
 }
 
 TEST_CASE("[Synth] Release (Multiple notes after pedal is down, release, cleared the delayed voices after)")
@@ -1141,7 +1143,7 @@ TEST_CASE("[Synth] Release (Multiple notes after pedal is down, release, cleared
     sortAll(requiredVelocities, actualVelocities);
     REQUIRE( requiredVelocities == actualVelocities );
 
-    REQUIRE( synth.getRegionView(1)->delayedSustainReleases.empty() );
+    REQUIRE( synth.getLayerView(1)->delayedSustainReleases_.empty() );
 }
 
 TEST_CASE("[Synth] Release (Multiple note ons during pedal down)")
@@ -1168,7 +1170,7 @@ TEST_CASE("[Synth] Release (Multiple note ons during pedal down)")
     }
     sortAll(requiredVelocities, actualVelocities);
     REQUIRE( requiredVelocities == actualVelocities );
-    REQUIRE( synth.getRegionView(1)->delayedSustainReleases.empty() );
+    REQUIRE( synth.getLayerView(1)->delayedSustainReleases_.empty() );
 }
 
 TEST_CASE("[Synth] No release sample after the main sample stopped sounding by default")
@@ -1203,7 +1205,7 @@ TEST_CASE("[Synth] No release sample after the main sample stopped sounding by d
     synth.cc(0, 64, 0);
     REQUIRE( synth.getNumActiveVoices() == 0 );
 
-    REQUIRE( synth.getRegionView(1)->delayedSustainReleases.empty() );
+    REQUIRE( synth.getLayerView(1)->delayedSustainReleases_.empty() );
 }
 
 TEST_CASE("[Synth] If rt_dead is active the release sample can sound after the attack sample died")
@@ -1238,7 +1240,7 @@ TEST_CASE("[Synth] If rt_dead is active the release sample can sound after the a
     synth.cc(0, 64, 0);
     REQUIRE( synth.getNumActiveVoices() == 0 );
 
-    REQUIRE( synth.getRegionView(1)->delayedSustainReleases.empty() );
+    REQUIRE( synth.getLayerView(1)->delayedSustainReleases_.empty() );
 }
 
 TEST_CASE("[Synth] sw_default works at a global level")