Shepard tone timbre is now a harmonic series (buzz).

Fixed exception from custom tablet destructor. May need to check for a memory leak now.

src/yaw-shepard/dsp.cpp

@@ -83,10 +83,10 @@ protected:
 		fParameters[idx] = val;
 		switch (idx) {
 		case ktpax:
-			synth.setFrequencyShift(val);
+			synth.setPhaseVelocity(val);
 			break;
 		case ktpay:
-			synth.setTargetRatio(val);
+			synth.setTimbre(val);
 			break;
 		case ktpaz:
 			break;

src/yaw-shepard/synth.cpp

@@ -7,12 +7,20 @@ Synth::Synth(double sampleRate){
 #define frac(x) ((x) - ((long)x))
 constexpr double MIN_VOLUME = 0.00001;
 
+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 )
 {
-  if( hz < 20.0 )       return 0.0;
+  if( hz < amin )       return 0.0;
-  if( hz < 440.0 )      return hz / 440.0;
+  if( hz < apiq )      {
-  if( hz < 10000.0 )    return (10000.0 - hz) / 9560.0;
+        double a = (hz - amin) / (apiq - amin);
+        return a * a;}
+  if( hz < amax )     {
+        double a  = 1.0 - (hz - apiq) / (amax - apiq);
+        return a * a;
+  }
   return 0.0;
 }
 
@@ -21,6 +29,26 @@ static constexpr double getAmplitude( double hz )
 static_assert( MIN_VOLUME > getAmplitude(10.0) );
 static_assert( MIN_VOLUME > getAmplitude(20000.0));
 
+//New fundamental is twice as high as old fundamental.
+//Even overtones become plain overtones.
+void Synth::shiftUp()
+{
+    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()
+{
+    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;
@@ -29,76 +57,53 @@ void Synth::process(float* output, const uint32_t frames)
     for(uint32_t i = 0; i < frames; i++){
 
         //Set pitch.
-        hz = hzFund *= hzShift;
+        hz = hzFund = spectrumPhase * fMin + fMin;
 
-        //Set timbre.
+        bool isOddHarmonic = true;
-        ratio = ratioSlewRate * ratio + (1.0 - ratioSlewRate) * targetRatio;
         
         for(uint voice = 0; voice < NUM_VOICES; ++voice){
             //Get new phase.
-            double phase = phases[(voice + idxFund) & VOICE_MASK];
+            double phase = phases[voice];
             phase += hz * sampleInterval;
             phase = frac(phase);
 
             //Anti-aliasing: don't bother rendering anything over the Nyquist rate.
             if( hz > hzNyq ) break;
-            output[i] += getAmplitude(hz) * sin(2.0 * M_PI * phase);
+
+            output[i] += (!isOddHarmonic + isOddHarmonic * spectrumPhase * spectrumPhase)   //Fade in odd harmonics.
+            * getAmplitude(hz)                                              //Frequency response.
+            * sin(2.0 * M_PI * phase);                                      //Additives.
 
             //Remember phase, move to higher overtone.
-            phases[(voice + idxFund) & VOICE_MASK] = phase;
+            phases[voice] = phase;
-            hz *= ratio * (voice + 1.0) / (voice + 2.0);
+            hz *= (voice + 2.0) / (voice + 1.0);
+            isOddHarmonic = !isOddHarmonic;
         }
 
         output[i] *= volume / static_cast<double>(NUM_VOICES);
+
+        //Wrapping.
+        spectrumPhase += spectrumPhaseVelocity * sampleInterval;
+        if( spectrumPhase > 1.0) shiftDown();
+        if( spectrumPhase < 0.0)   shiftUp();
     }
 
-    //Make timbre cyclical.
-    if( hzShift < 1.0 )
-    {
-        //Pitch low and decreasing, shift bottom voices to top.
-        while( getAmplitude(hz) > MIN_VOLUME
-            && getAmplitude(hzFund) < MIN_VOLUME)
-        {
-            ++idxFund;
-            hz *= 2.0 * ratio;
-            hzFund *= 2.0 * ratio;
-        }
-    }
-
-    if( (hzShift > 1.0) || (targetRatio > ratio))
-    {
-        //Pitch high and increasing. Shift top voices to bottom.
-        while( getAmplitude(hz) < MIN_VOLUME
-            && getAmplitude(hzFund) > MIN_VOLUME)
-        {
-            --idxFund;
-            hz /= 2.0 * ratio;
-            hzFund /= 2.0 * ratio;
-        }
-    }
 }
 
 void Synth::setSampleRate(double oldRate, double newRate){
     sampleInterval = 1.0 / newRate;
     hzNyq = newRate / 2;
-    ratioSlewRate = pow(ratioSlewRate, oldRate / newRate);
-    hzShift = pow(hzShift, newRate / oldRate);
 }
 
 //Takes value from 0 to 1 representing frequency shift factor.
 //0 : lower one octave per second
 //1 : raise one octave per second
-void Synth::setFrequencyShift(double in){
+void Synth::setPhaseVelocity(double in){
-    hzShift = exp2(2.0 * (in - 0.5) * sampleInterval);
+    spectrumPhaseVelocity = 2.0 * (in - 0.5);
 }
 
-static constexpr double minRatio = 1.0;
+void Synth::setTimbre(double in){
-static constexpr double maxRatio = 1.05;
+    
-//Slew to given inharmonicity ratio.
-//0 : next voice is exactly harmonic.
-//1 : next voice is 5% inharmonic.
-void Synth::setTargetRatio(double in){
-    targetRatio = minRatio + in * (maxRatio - minRatio);
 }
 
 void Synth::setVolume(double in){

src/yaw-shepard/synth.h

@@ -7,7 +7,7 @@ struct Voice
     double phase;
 };
 
-constexpr unsigned int NUM_VOICES = 64;
+constexpr unsigned int NUM_VOICES = 256;
 constexpr unsigned int VOICE_MASK = NUM_VOICES - 1;
 
 class Synth
@@ -15,23 +15,26 @@ class Synth
 public:
     explicit Synth(double sampleRate);
     void process(float *output, uint32_t frames);
-    void setFrequencyShift(double in);
+    void setPhaseVelocity(double in);
-    void setTargetRatio(double in);
+    void setTimbre(double in);
     void setSampleRate(double oldRate, double newRate);
     void setVolume(double in);
+    void shiftUp();
+    void shiftDown();
 
 private:
     //Phase must persist between run invocation.
-    //Phase of each voice, considered as a period function on the unit interval.
+    //Phase of each voice, considered a function on the unit circle.
     std::array<double, NUM_VOICES> phases = {0};
-    //Index of lowest voice in phase array.
-    unsigned int idxFund = 0;
     float volume = 0.0f;
-    double hzFund = 32.7;
+    //Parameter in unit circle controlling pitch (varies by one octave).
-    double hzShift = 1.0;
+    double spectrumPhase = 1.0f;
+    //Revolutions per second of spectrum phase.
+    double spectrumPhaseVelocity = 0.0;
+    //Lowest fundamental frequency of blit.
+    static inline constexpr double fMin = 55.0;
+    //Current fundamental frequency of blit.
+    double hzFund = fMin;
     double hzNyq = 24000.0;
-    double ratio = 2.0;
-    double targetRatio = 2.0;
-    double ratioSlewRate = 0.99999;
     double sampleInterval = 1.0 / 48000.0;
 };

src/yaw-shepard/tablet.h

@@ -30,7 +30,6 @@ struct Packet {
 class Tablet {
 public:
 	Tablet(uintptr_t handle);
-	~Tablet();
     bool GetPacket( Packet &pkt );
 	bool initialized;
 	std::string errormsg = "";

src/yaw-shepard/wintab.cpp

@@ -18,10 +18,10 @@ Tablet::Tablet(uintptr_t handle)
 	NewContext(hwnd);
 }
 
-Tablet::~Tablet() {
+/*Tablet::~Tablet() {
-	if (hctx) { gpWTClose(hctx); }
+	// if (hctx) { gpWTClose(hctx); }
 	UnloadWintab();
-}
+}*/
 
 bool Tablet::GetPacket( Packet& packet ) {
 	//Serial number of newest packet.
@@ -54,7 +54,7 @@ void Tablet::NewContext(HWND hwnd) {
 	AXIS TabletZ = { 0 };
 	AXIS TabletPressure = { 0 };
 	gpWTInfoA(WTI_DEFCONTEXT, 0, &ctx);
-	ctx.lcOptions |= CXO_MESSAGES; //TODO: checker çela
+	ctx.lcOptions |= CXO_MESSAGES; //TODO: checker <EFBFBD>ela
 	ctx.lcPktData = PACKETDATA;
 	ctx.lcPktMode = 0;