fixed filter issues

src/synth/Filter.cpp

@@ -15,7 +15,7 @@ void Filter::setSampleRate(float sampleRate) {
 
 void Filter::setParams(Type type, float frequency, float q) {
     type_ = type;
-    frequency_ = frequency;
+    frequency_ = std::min(frequency, sampleRate_ / 2.0f * 0.999f);
     q_ = q;
     calculateCoefficients();
 }
@@ -23,11 +23,11 @@ void Filter::setParams(Type type, float frequency, float q) {
 float Filter::biquadProcess(float in) {
 
     // calculate filtered sample
-    float out = a0_ * in + z1_;
+    float out = b0_ * in + z1_;
     
     // update states
-    z1_ = a1_ * in - b1_ * out + z2_;
-    z2_ = a2_ * in - b2_ * out;
+    z1_ = b1_ * in - a1_ * out + z2_;
+    z2_ = b2_ * in - a2_ * out;
 
     return out;
 }
@@ -73,11 +73,11 @@ void Filter::calculateCoefficients() {
     }
 
     // Normalize
-    a0_ = b0 / a0;
-    a1_ = b1 / a0;
-    a2_ = b2 / a0;
-    b1_ = a1 / a0;
-    b2_ = a2 / a0;
+    b0_ = b0 / a0;
+    b1_ = b1 / a0;
+    b2_ = b2 / a0;
+    a1_ = a1 / a0;
+    a2_ = a2 / a0;
     
 }
 

src/synth/Filter.h

@@ -40,7 +40,7 @@ private:
     float q_ = 0.707f;
 
     // biquad filter structure
-    float a0_, a1_, a2_, b1_, b2_;
+    float a1_, a2_, b0_, b1_, b2_;
     float z1_, z2_;
 
 };

src/synth/Synth.cpp

@@ -87,8 +87,9 @@ void Synth::process(float* out, uint32_t nFrames, uint32_t sampleRate) {
         gainEnvelope_.set(getParam(ParamId::Osc1VolumeEnvA), getParam(ParamId::Osc1VolumeEnvD), getParam(ParamId::Osc1VolumeEnvS), getParam(ParamId::Osc1VolumeEnvR));
         cutoffEnvelope_.set(getParam(ParamId::FilterCutoffEnvA), getParam(ParamId::FilterCutoffEnvD), getParam(ParamId::FilterCutoffEnvS), getParam(ParamId::FilterCutoffEnvR));
         resonanceEnvelope_.set(getParam(ParamId::FilterResonanceEnvA), getParam(ParamId::FilterResonanceEnvD), getParam(ParamId::FilterResonanceEnvS), getParam(ParamId::FilterResonanceEnvR));
-        float gain = gainEnvelope_.process();
-        filter_.setParams(Filter::Type::BiquadLowpass, cutoffEnvelope_.process(), resonanceEnvelope_.process());
+        float gainEnv = gainEnvelope_.process();
+        float cutoffEnv = cutoffEnvelope_.process();
+        float resonanceEnv = resonanceEnvelope_.process();
         // TODO: envelope is shared between all notes so this sequence involves a note change but only one envelope attack:
         // NOTE_A_ON > NOTE_B_ON > NOTE_A_OFF and note B starts playing part-way through note A's envelope 
 
@@ -106,6 +107,8 @@ void Synth::process(float* out, uint32_t nFrames, uint32_t sampleRate) {
         float pitchOffset = 0.5f;
         float phaseInc = pitchOffset * 2.0f * M_PI * frequency_ / static_cast<float>(sampleRate);
 
+        float gain = gainEnv * getParam(ParamId::Osc1Volume);
+
         // sample generation
         // TODO: wavetables
         // TODO: wavetables should be scaled by their RMS for equal loudness (prelim standard = 0.707)
@@ -132,6 +135,8 @@ void Synth::process(float* out, uint32_t nFrames, uint32_t sampleRate) {
         }
 
         // filter sample
+        float cutoffFreq = cutoffEnv * pow(2.0f, getParam(ParamId::FilterCutoff)) * frequency_;
+        filter_.setParams(Filter::Type::BiquadLowpass, cutoffFreq, resonanceEnv * getParam(ParamId::FilterResonance));
         sampleOut = filter_.biquadProcess(sampleOut);
 
         // write to buffer