Revert to earlier timbre.

src/yaw-shepard/dsp.cpp

@@ -93,7 +93,7 @@ protected:
 			synth.setPhaseVelocity(val);
 			break;
 		case ktpay:
-			synth.setTimbre(val);
+			synth.setPitchOffset(val);
 			break;
 		case ktpaz:
 			break;

src/yaw-shepard/synth.cpp

@@ -11,7 +11,7 @@ static constexpr double amin = 50;
 static constexpr double apiq = 500;
 static constexpr double amax = 10000;
 //Volume of voice as a function of sample rate independent frequency.
-static constexpr double getAmplitude( double hz )
+static constexpr inline float getAmplitude( double hz )
 {
   if( hz < amin )       return 0.0;
   if( hz < apiq )      {
@@ -24,8 +24,13 @@ static constexpr double getAmplitude( double hz )
   return 0.0;
 }
 
+//Interpolation function on unit interval with good regularity as a function on S^1.
+static constexpr inline float smooth( double x )
+{
+    return x * x * x;//(3.0 * x - 2.0);
+}
+
 //Sanity checks: voices should become silent outside audible frequencies.
-//Voice index code will loop infinitely if these fail.
 static_assert( MIN_VOLUME > getAmplitude(10.0) );
 static_assert( MIN_VOLUME > getAmplitude(20000.0));
 
@@ -33,54 +38,45 @@ static_assert( MIN_VOLUME > getAmplitude(20000.0));
 //Even overtones become plain overtones.
 void Synth::shiftUp()
 {
+    tablePhase *= 2.0;
     spectrumPhase += 1.0;
-    for(uint voice = 0; voice < NUM_VOICES; ++voice){
-        phases[voice] = phases[(2 * voice + 1) & VOICE_MASK];
-    }
 }
 
 //New fundamental is half as high as old fundamental.
 //Overtones become even overtones.
 void Synth::shiftDown()
 {
+    tablePhase /= 2.0;
     spectrumPhase -= 1.0;
-    for(uint voice = NUM_VOICES / 2 - 1; voice < NUM_VOICES; --voice){
-        phases[voice * 2 + 1] = phases[voice];
-    }
 }
 
 void Synth::process(float* output, const uint32_t frames)
 {
-    double hz;
-
     //Render.
     for(uint32_t i = 0; i < frames; i++){
 
         //Set pitch.
-        hz = hzFund = exp2(spectrumPhase) * fMin;
+        hzFund = exp2(spectrumPhase) * fMin;
+        
+        tablePhase += hzFund * sampleInterval;
+        tablePhase = frac(tablePhase);
 
         bool isOddHarmonic = true;
         
         for(uint voice = 0; voice < NUM_VOICES; ++voice){
-            //Get new phase.
-            double phase = phases[voice];
-            phase += hz * sampleInterval;
-            phase = frac(phase);
 
+            double voicePhase = 2.0 * M_PI * tablePhase * (voice + 1.0);
             //Anti-aliasing: don't bother rendering anything over the Nyquist rate.
-            if( hz > hzNyq ) break;
+            if( hzFund * (voice + 1.0) > hzNyq ) break;
 
-            output[i] += (!isOddHarmonic + isOddHarmonic * spectrumPhase * spectrumPhase)   //Fade in odd harmonics.
-            * getAmplitude(hz)                                              //Frequency response.
-            * sin(2.0 * M_PI * phase);                                      //Additives.
+            output[i] += (!isOddHarmonic + isOddHarmonic * smooth(spectrumPhase))   //Fade in odd harmonics.
+            * getAmplitude(hzFund * (voice + 1.0))                                  //Frequency response.
+            * sinf(static_cast<float>(voicePhase));                                 //Additives.
 
-            //Remember phase, move to higher overtone.
-            phases[voice] = phase;
-            hz *= (voice + 2.0) / (voice + 1.0);
             isOddHarmonic = !isOddHarmonic;
         }
 
-        output[i] *= 32 * volume / static_cast<double>(NUM_VOICES);
+        output[i] *= fMin * volume / static_cast<float>(8 * NUM_VOICES);
 
         //Wrapping.
         spectrumPhase += spectrumPhaseVelocity * sampleInterval;
@@ -95,7 +91,7 @@ void Synth::setSampleRate(double oldRate, double newRate){
     hzNyq = newRate / 2;
 }
 
-//Takes value from 0 to 1 representing frequency shift factor.
+//Takes value from 0 to 1 representing rate of wrapping pitch increase.
 //0 : lower one octave per second
 //1 : raise one octave per second
 void Synth::setPhaseVelocity(double in){
@@ -103,11 +99,12 @@ void Synth::setPhaseVelocity(double in){
 }
 
 //Vary pitch of fundamental in a non-wrapping kinda way.
-//Current range is six octaves, current bottom is 110.0 Hz (A3)
-void Synth::setTimbre(double in){
-    fMin = exp2(in * 2.0) * 110.0;
+//Current range is six octaves, current bottom is 13.75 Hz (A0)
+void Synth::setPitchOffset(double in){
+    fMin = exp2(in * 6.0) * 13.75;
 }
 
+
 void Synth::setVolume(double in){
     volume = in;
 }

src/yaw-shepard/synth.h

@@ -1,12 +1,6 @@
 #include "DistrhoPlugin.hpp"
 #include <array>
 
-struct Voice
-{
-    double hz;
-    double phase;
-};
-
 constexpr unsigned int NUM_VOICES = 512;
 constexpr unsigned int VOICE_MASK = NUM_VOICES - 1;
 
@@ -16,7 +10,7 @@ public:
     explicit Synth(double sampleRate);
     void process(float *output, uint32_t frames);
     void setPhaseVelocity(double in);
-    void setTimbre(double in);
+    void setPitchOffset(double in);
     void setSampleRate(double oldRate, double newRate);
     void setVolume(double in);
     void shiftUp();
@@ -26,9 +20,9 @@ public:
     double hzFund = fMin;
 
 private:
-    //Phase must persist between run invocation.
-    //Phase of each voice, considered a function on the unit circle.
-    std::array<double, NUM_VOICES> phases = {0};
+    //Phase of wavetable.
+    double tablePhase = 0.0;
+    double fmPhase = 0.0;
     float volume = 0.0f;
     //Parameter in unit circle controlling pitch (varies by one octave).
     double spectrumPhase = 1.0f;
@@ -37,6 +31,9 @@ private:
     //Lowest fundamental frequency of blit.
     double fMin = 55.0;
 
+    //Parameter stretching the overtone series.
+    double inharmonicity = 1.001;
+
     double hzNyq = 24000.0;
     double sampleInterval = 1.0 / 48000.0;
 };

src/yaw-shepard/ui.cpp

@@ -177,7 +177,7 @@ void TabUI::onNanoDisplay()
 	beginPath();
 	fillColor(200, 200, 200);
 	textBox(0.f, 15.f, 250.f,
-			std::format("Frequency: {:.3f}\nNearest: {}\n",
+			std::format("Frequency: {:.3f}\nNearest: {:.3f}\n",
 						hz, scale.getNearestNoteNumber(hz))
 				.c_str(),
 			nullptr);