Simpler power/envelope followerThis one is much cheaper...

src/sfizz/Config.h

@@ -57,7 +57,7 @@ namespace config {
     constexpr Oversampling defaultOversamplingFactor { Oversampling::x1 };
     constexpr float A440 { 440.0 };
     constexpr size_t powerHistoryLength { 16 };
-    constexpr float filteredEnvelopeCutoff { 5 };
+    constexpr float powerFollowerFactor { 10 };
     constexpr uint16_t numCCs { 512 };
     constexpr int maxCurves { 256 };
     constexpr int chunkSize { 1024 };

src/sfizz/Voice.cpp

@@ -30,9 +30,6 @@ sfz::Voice::Voice(int voiceNumber, sfz::Resources& resources)
 
     gainSmoother.setSmoothing(config::gainSmoothing, sampleRate);
     xfadeSmoother.setSmoothing(config::xfadeSmoothing, sampleRate);
-
-    for (auto & filter : channelEnvelopeFilters)
-        filter.setGain(vaGain(config::filteredEnvelopeCutoff, sampleRate));
 }
 
 sfz::Voice::~Voice()
@@ -246,20 +243,19 @@ void sfz::Voice::setSampleRate(float sampleRate) noexcept
     gainSmoother.setSmoothing(config::gainSmoothing, sampleRate);
     xfadeSmoother.setSmoothing(config::xfadeSmoothing, sampleRate);
 
-    for (auto & filter : channelEnvelopeFilters)
-        filter.setGain(vaGain(config::filteredEnvelopeCutoff, sampleRate));
-
     for (WavetableOscillator& osc : waveOscillators)
         osc.init(sampleRate);
 
     for (auto& lfo : lfos)
         lfo->setSampleRate(sampleRate);
+
+    trackingFactor = samplesPerBlock / sampleRate * config::powerFollowerFactor;
 }
 
 void sfz::Voice::setSamplesPerBlock(int samplesPerBlock) noexcept
 {
     this->samplesPerBlock = samplesPerBlock;
-    this->minEnvelopeDelay = samplesPerBlock / 2;
+    this->trackingFactor = samplesPerBlock / sampleRate * config::powerFollowerFactor;
 }
 
 void sfz::Voice::renderBlock(AudioSpan<float> buffer) noexcept
@@ -736,10 +732,7 @@ void sfz::Voice::reset() noexcept
     floatPositionOffset = 0.0f;
     noteIsOff = false;
 
-    for (auto& f : channelEnvelopeFilters)
-        f.reset();
-
-    for (auto& p : smoothedChannelEnvelopes)
+    for (auto& p : meanChannelPowers)
         p = 0.0f;
 
     filters.clear();
@@ -770,9 +763,9 @@ void sfz::Voice::removeVoiceFromRing() noexcept
     nextSisterVoice = this;
 }
 
-float sfz::Voice::getAverageEnvelope() const noexcept
+float sfz::Voice::getAveragePower() const noexcept
 {
-    return max(smoothedChannelEnvelopes[0], smoothedChannelEnvelopes[1]);
+    return max(meanChannelPowers[0], meanChannelPowers[1]);
 }
 
 bool sfz::Voice::releasedOrFree() const noexcept
@@ -869,16 +862,14 @@ void sfz::Voice::setupOscillatorUnison()
 
 void sfz::Voice::updateChannelPowers(AudioSpan<float> buffer)
 {
-    assert(smoothedChannelEnvelopes.size() == channelEnvelopeFilters.size());
-    assert(buffer.getNumChannels() <= channelEnvelopeFilters.size());
     if (buffer.getNumFrames() == 0)
         return;
 
-    for (unsigned i = 0; i < smoothedChannelEnvelopes.size(); ++i) {
+    const float factor = buffer.getNumFrames() / samplesPerBlock * trackingFactor;
+    for (unsigned i = 0; i < meanChannelPowers.size(); ++i) {
         const auto input = buffer.getConstSpan(i);
-        for (unsigned s = 0; s < buffer.getNumFrames(); ++s)
-            smoothedChannelEnvelopes[i] =
-                channelEnvelopeFilters[i].tickLowpass(std::abs(input[s]));
+        const float meanPower = sfz::meanSquared(input);
+        meanChannelPowers[i] = meanChannelPowers[i] * (1 - factor) + meanPower * factor;
     }
 }
 

src/sfizz/Voice.h

@@ -261,7 +261,7 @@ public:
      *
      * @return float
      */
-    float getAverageEnvelope() const noexcept;
+    float getAveragePower() const noexcept;
     /**
      * @brief Get the position of the voice in the source, in samples
      *
@@ -450,7 +450,6 @@ private:
     FilePromisePtr currentPromise { nullptr };
 
     int samplesPerBlock { config::defaultSamplesPerBlock };
-    int minEnvelopeDelay { config::defaultSamplesPerBlock / 2 };
     float sampleRate { config::defaultSampleRate };
 
     Resources& resources;
@@ -486,10 +485,8 @@ private:
     Smoother xfadeSmoother;
     void resetSmoothers() noexcept;
 
-    std::array<OnePoleFilter<float>, 2> channelEnvelopeFilters;
-    std::array<float, 2> smoothedChannelEnvelopes;
-
-    HistoricalBuffer<float> powerHistory { config::powerHistoryLength };
+    float trackingFactor { config::defaultSamplesPerBlock / config::defaultSampleRate * config::powerFollowerFactor };
+    std::array<float, 2> meanChannelPowers;
     LEAK_DETECTOR(Voice);
 };
 

src/sfizz/VoiceStealing.cpp

@@ -13,12 +13,12 @@ sfz::Voice* sfz::VoiceStealing::steal(absl::Span<sfz::Voice*> voices) noexcept
     // Start of the voice stealing algorithm
     absl::c_stable_sort(voices, voiceOrdering);
 
-    const auto sumEnvelope = absl::c_accumulate(voices, 0.0f, [](float sum, const Voice* v) {
-        return sum + v->getAverageEnvelope();
+    const auto sumPower = absl::c_accumulate(voices, 0.0f, [](float sum, const Voice* v) {
+        return sum + v->getAveragePower();
     });
-    // We are checking the envelope to try and kill voices with relative low contribution
+    // We are checking the power to try and kill voices with relative low contribution
     // to the output compared to the rest.
-    const auto envThreshold = sumEnvelope
+    const auto powerThreshold = sumPower
         / static_cast<float>(voices.size()) * config::stealingEnvelopeCoeff;
     // We are checking the age so that voices have the time to build up attack
     // This is not perfect because pad-type voices will take a long time to output
@@ -37,12 +37,12 @@ sfz::Voice* sfz::VoiceStealing::steal(absl::Span<sfz::Voice*> voices) noexcept
             break;
         }
 
-        float maxEnvelope { 0.0f };
+        float maxPower { 0.0f };
         SisterVoiceRing::applyToRing(ref, [&](Voice* v) {
-            maxEnvelope = max(maxEnvelope, v->getAverageEnvelope());
+            maxPower = max(maxPower, v->getAveragePower());
         });
 
-        if (maxEnvelope < envThreshold) {
+        if (maxPower < powerThreshold) {
             returnedVoice = ref;
             break;
         }