Add the gain effect

src/CMakeLists.txt

@@ -26,6 +26,7 @@ set (SFIZZ_SOURCES
     sfizz/effects/Lofi.cpp
     sfizz/effects/Limiter.cpp
     sfizz/effects/Rectify.cpp
+    sfizz/effects/Gain.cpp
 )
 include (SfizzSIMDSourceFiles)
 

src/sfizz/Effects.cpp

@@ -16,6 +16,7 @@
 #include "effects/Lofi.h"
 #include "effects/Limiter.h"
 #include "effects/Rectify.h"
+#include "effects/Gain.h"
 #include <algorithm>
 
 namespace sfz {
@@ -31,6 +32,7 @@ void EffectFactory::registerStandardEffectTypes()
 
     // extensions (book)
     registerEffectType("rectify", fx::Rectify::makeInstance);
+    registerEffectType("gain", fx::Gain::makeInstance);
 }
 
 void EffectFactory::registerEffectType(absl::string_view name, Effect::MakeInstance& make)

src/sfizz/effects/Gain.cpp

@@ -0,0 +1,73 @@
+// 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
+
+
+/**
+   Note(jpc): this effect is book-only, mentioned but not documented
+
+   Note(jpc): implementation status
+
+- [x] gain
+- [ ] gain_oncc
+ */
+
+#include "Gain.h"
+#include "Opcode.h"
+#include "SIMDHelpers.h"
+#include "absl/memory/memory.h"
+
+namespace sfz {
+namespace fx {
+
+    void Gain::setSampleRate(double sampleRate)
+    {
+        (void)sampleRate;
+    }
+
+    void Gain::setSamplesPerBlock(int samplesPerBlock)
+    {
+        _tempBuffer.resize(samplesPerBlock);
+    }
+
+    void Gain::clear()
+    {
+    }
+
+    void Gain::process(const float* const inputs[], float* const outputs[], unsigned nframes)
+    {
+        const float baseGain = _gain;
+
+        absl::Span<float> gains = _tempBuffer.getSpan(0);
+        std::fill(gains.begin(), gains.end(), baseGain);
+
+        // to linear
+        for (unsigned i = 0; i < nframes; ++i)
+            gains[i] = std::pow(10.0f, 0.05f * gains[i]);
+
+        for (unsigned c = 0; c < EffectChannels; ++c) {
+            absl::Span<const float> input { inputs[c], nframes };
+            absl::Span<float> output { outputs[c], nframes };
+            sfz::applyGain(absl::Span<const float> { gains }, input, output);
+        }
+    }
+
+    std::unique_ptr<Effect> Gain::makeInstance(absl::Span<const Opcode> members)
+    {
+        auto fx = absl::make_unique<Gain>();
+
+        for (const Opcode& opc : members) {
+            switch (opc.lettersOnlyHash) {
+            case hash("gain"):
+                setValueFromOpcode(opc, fx->_gain, {-96.0f, 96.0f});
+                break;
+            }
+        }
+
+        return CXX11_MOVE(fx);
+    }
+
+} // namespace fx
+} // namespace sfz

src/sfizz/effects/Gain.h

@@ -0,0 +1,50 @@
+// 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 "Effects.h"
+
+namespace sfz {
+namespace fx {
+
+    /**
+     * @brief Gain effect
+     */
+    class Gain : public Effect {
+    public:
+        /**
+         * @brief Initializes with the given sample rate.
+         */
+        void setSampleRate(double sampleRate) override;
+
+        /**
+         * @brief Sets the maximum number of frames to render at a time. The actual
+         * value can be lower but should never be higher.
+         */
+        void setSamplesPerBlock(int samplesPerBlock) override;
+
+        /**
+         * @brief Reset the state to initial.
+         */
+        void clear() override;
+
+        /**
+         * @brief Copy the input signal to the output
+         */
+        void process(const float* const inputs[], float* const outputs[], unsigned nframes) override;
+
+        /**
+          * @brief Instantiates given the contents of the <effect> block.
+          */
+        static std::unique_ptr<Effect> makeInstance(absl::Span<const Opcode> members);
+
+    private:
+        float _gain = 0; // in dB
+        AudioBuffer<float, 1> _tempBuffer { 1, config::defaultSamplesPerBlock };
+    };
+
+} // namespace fx
+} // namespace sfz