Sustain tweaks:

- Separate the sustain value from the sustain threshold after which the envelope goes from decay to sustain
- If the sustain value is set to 0, the envelope is freerunning

src/sfizz/ADSREnvelope.cpp

@@ -48,12 +48,14 @@ void ADSREnvelope<Type>::reset(const EGDescription& desc, const Region& region,
     this->hold = secondsToSamples(desc.getHold(state, velocity));
     this->peak = 1.0;
     this->sustain = normalizePercents(desc.getSustain(state, velocity));
-    this->sustain = max(this->sustain, config::virtuallyZero);
     this->start = this->peak * normalizePercents(desc.getStart(state, velocity));
 
     releaseDelay = 0;
+    sustainThreshold = this->sustain + config::virtuallyZero;
     shouldRelease = false;
-    freeRunning = ((region.trigger == SfzTrigger::release)
+    freeRunning = (
+        (region.trigger == SfzTrigger::release)
+        || (this->sustain == 0.0f)
         || (region.trigger == SfzTrigger::release_key)
         || (region.loopMode == SfzLoopMode::one_shot && (region.isGenerator() || region.oscillator)));
     currentValue = this->start;
@@ -89,7 +91,7 @@ Type ADSREnvelope<Type>::getNextValue() noexcept
         // fallthrough
     case State::Decay:
         currentValue *= decayRate;
-        if (currentValue > sustain)
+        if (currentValue > sustainThreshold )
             return currentValue;
 
         currentState = State::Sustain;
@@ -159,7 +161,7 @@ void ADSREnvelope<Type>::getBlock(absl::Span<Type> output) noexcept
         case State::Decay:
             while (count < size && (currentValue *= decayRate) > sustain)
                 output[count++] = currentValue;
-            if (currentValue <= sustain) {
+            if (currentValue <= sustainThreshold) {
                 currentValue = sustain;
                 currentState = State::Sustain;
             }

src/sfizz/ADSREnvelope.h

@@ -102,6 +102,7 @@ private:
     Type start { 0 };
     Type peak { 0 };
     Type sustain { 0 };
+    Type sustainThreshold { config::virtuallyZero };
     int releaseDelay { 0 };
     bool shouldRelease { false };
     bool freeRunning { false };

tests/SynthT.cpp

@@ -1167,6 +1167,55 @@ TEST_CASE("[Synth] end=-1 voices are immediately killed after triggering but the
     REQUIRE( numPlayingVoices(synth) == 0 );
 }
 
+TEST_CASE("[Synth] end=0 voices are immediately killed after triggering but they kill other voices")
+{
+    sfz::Synth synth;
+    sfz::AudioBuffer<float> buffer { 2, 256 };
+
+    synth.loadSfzString(fs::current_path(), R"(
+        <region> key=60 end=0 sample=*sine
+        <region> key=61 end=0 sample=*silence
+        <region> key=62 sample=*sine off_by=2
+        <region> key=63 end=0 sample=*saw group=2
+    )");
+    synth.noteOn(0, 60, 85);
+    REQUIRE( synth.getNumActiveVoices(true) == 0 );
+    synth.noteOn(0, 61, 85);
+    REQUIRE( synth.getNumActiveVoices(true) == 0 );
+    synth.noteOn(0, 62, 85);
+    REQUIRE( synth.getNumActiveVoices(true) == 1 );
+    REQUIRE( numPlayingVoices(synth) == 1 );
+    synth.noteOn(1, 63, 85);
+    synth.renderBlock(buffer);
+    REQUIRE( numPlayingVoices(synth) == 0 );
+}
+
+TEST_CASE("[Synth] ampeg_sustain = 0 puts the ampeg envelope in free-running mode, which kills the voice almost instantly in most cases")
+{
+    sfz::Synth synth;
+    sfz::AudioBuffer<float> buffer { 2, 256 };
+
+    synth.loadSfzString(fs::current_path(), R"(
+        <region> key=60 sample=*sine ampeg_sustain=0
+        <region> key=61 sample=*sine ampeg_sustain=0 ampeg_attack=0.1 ampeg_decay=0.1
+    )");
+
+    synth.noteOn(0, 60, 85);
+    REQUIRE( synth.getNumActiveVoices(true) == 1 );
+    synth.renderBlock(buffer);
+    REQUIRE( synth.getNumActiveVoices(true) == 0 );
+    synth.noteOn(0, 61, 85);
+    REQUIRE( synth.getNumActiveVoices(true) == 1 );
+    // Render a bit; this does not kill the voice
+    for (unsigned i = 0; i < 5; ++i)
+        synth.renderBlock(buffer);
+    REQUIRE( synth.getNumActiveVoices(true) == 1 );
+    // Render about half a second
+    for (unsigned i = 0; i < 100; ++i)
+        synth.renderBlock(buffer);
+    REQUIRE( synth.getNumActiveVoices(true) == 0 );
+}
+
 TEST_CASE("[Synth] Off by standard")
 {
     sfz::Synth synth;
@@ -1222,4 +1271,3 @@ TEST_CASE("[Synth] Off by same note")
     auto playingVoices = getPlayingVoices(synth);
     REQUIRE( playingVoices.front()->getRegion()->sampleId.filename() == "*triangle" );
 }
-