Added synthesis.

src/yaw-shepard/DistrhoPluginInfo.h

@@ -2,22 +2,15 @@
 #define DISTRHO_PLUGIN_INFO_H_INCLUDED
 
 #define DISTRHO_PLUGIN_BRAND "yaw-audio"
-#define DISTRHO_PLUGIN_NAME  "yaw-tab"
-#define DISTRHO_PLUGIN_URI   "https://yaw.man/plugins/yaw-tab"
+#define DISTRHO_PLUGIN_NAME  "yaw-shepard"
+#define DISTRHO_PLUGIN_URI   "https://yaw.man/plugins/yaw-shepard"
 
 #define DISTRHO_PLUGIN_HAS_UI       1
 #define DISTRHO_PLUGIN_IS_RT_SAFE   1
 #define DISTRHO_PLUGIN_NUM_INPUTS   0
-#define DISTRHO_PLUGIN_NUM_OUTPUTS  2
+#define DISTRHO_PLUGIN_NUM_OUTPUTS  1
 #define DISTRHO_UI_USE_NANOVG       1
 
-// only checking if supported, not actually used
-#define DISTRHO_PLUGIN_WANT_PARAMETER_VALUE_CHANGE_REQUEST 1
-
-#ifdef __MOD_DEVICES__
-#define DISTRHO_PLUGIN_USES_MODGUI  1
-#endif
-
 enum Parameters {
     ktpax = 0,
     ktpay,

src/yaw-shepard/dsp.cpp

@@ -1,4 +1,5 @@
 #include "DistrhoPlugin.hpp"
+#include "synth.h"
 
 START_NAMESPACE_DISTRHO
 
@@ -7,19 +8,18 @@ class TabPlugin : public Plugin
 public:
 	TabPlugin()
 		: Plugin(kParameterCount, 0, 0),
-		sampleRate(getSampleRate())
+		sampleRate(getSampleRate()),
+		synth(sampleRate),
+		fParameters { 0 }
 	{
-		// clear all parameters
-		std::memset(fParameters, 0, sizeof(float) * kParameterCount);
-
 	}
 
 protected:
-	const char* getLabel() const override { return "yaw-tab-shepard"; }
-	const char* getDescription() const override { return "Drawing tablet Shepard buzz tone"; }
+	const char* getLabel() const override { return "yaw-shepard"; }
+	const char* getDescription() const override { return "Generalized Shepard tone, tablet UI"; }
 	const char* getMaker() const override { return "yaw-audio"; }
 	const char* getHomePage() const override { return "https://yaw.man/plugins/yaw-tab"; }
-	const char* getLicense() const override { return "ISC"; }
+	const char* getLicense() const override { return "Fuck You Pay Me"; }
 	uint32_t    getVersion() const override { return d_version(1, 0, 0); }
 	int64_t     getUniqueId() const override { return d_cconst('y', 's', 'p', 'd'); }
 
@@ -69,6 +69,7 @@ protected:
 
 	void sampleRateChanged(double newRate) override
 	{
+		synth.setSampleRate(sampleRate, newRate);
 		sampleRate = newRate;
 	}
 
@@ -82,14 +83,15 @@ protected:
 		fParameters[idx] = val;
 		switch (idx) {
 		case ktpax:
-			period = 0.02f * val * static_cast<float>(sampleRate);
+			synth.setFrequencyShift(val);
 			break;
 		case ktpay:
+			synth.setTargetRatio(val);
 			break;
 		case ktpaz:
 			break;
 		case ktpap:
-			volume = val;
+			synth.setVolume(val);
 			break;
 		case kParameterButtonA:
 			break;
@@ -100,30 +102,17 @@ protected:
 
 	void run(const float** inputs, float** outputs, uint32_t frames) override
 	{
-
-		for (uint32_t i = 0; i < frames; ++i) {
-			counter++;
-			if (counter > period) {
-				outputs[0][i] = outputs[1][i] = volume;
-				counter = 0;
-			}
-			else {
-				outputs[0][i] = outputs[1][i] = 0.0f;
-			}
-		}
-
+		synth.process(*outputs, frames);
 		parity = !parity;
 		fParameters[kParameterTime] += parity ? 1 : -1;
 	}
 
 private:
 	float fParameters[kParameterCount];
-	float period = 0.f;
-	float counter = 0.f;
-	float volume = 0.f;
 	double sampleRate;
 	bool parity = false;
 
+	Synth synth;
 	DISTRHO_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR(TabPlugin)
 };
 

src/yaw-shepard/synth.cpp

@@ -0,0 +1,104 @@
+#include "synth.h"
+
+Synth::Synth(double sampleRate){
+    setSampleRate(48000.0, sampleRate);
+}
+
+#define frac(x) ((x) - ((long)x))
+constexpr double MIN_VOLUME = 0.00001;
+
+//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 < 440.0 )      return hz / 440.0;
+  if( hz < 16000.0 )    return (16000.0 - hz) / 15560.0;
+  return 0.0;
+}
+
+//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));
+
+void Synth::process(float* output, const uint32_t frames)
+{
+    double hz;
+
+    //Render.
+    for(uint32_t i = 0; i < frames; i++){
+
+        //Set pitch.
+        hz = hzFund *= hzShift;
+
+        //Set timbre.
+        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];
+            phase += hz * sampleInterval;
+            phase = frac(phase);
+
+            //Don't bother rendering anything over the Nyquist rate.
+            if( hz > hzNyq ) break;
+            output[i] += getAmplitude(hz) * sin(2.0 * M_PI * phase);
+
+            //Remember phase, move to higher overtone.
+            phases[(voice + idxFund) & VOICE_MASK] = phase;
+            hz *= ratio;
+        }
+
+        output[i] *= volume;
+    }
+
+    //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 *= ratio;
+            hzFund *= 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 /= ratio;
+            hzFund /= ratio;
+        }
+    }
+}
+
+void Synth::setSampleRate(double oldRate, double newRate){
+    sampleInterval = 1.0 / newRate;
+    hzNyq = newRate / 2;
+    ratioSlewRate *= newRate / oldRate;
+    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){
+    hzShift = exp2(2.0 * (in - 0.5) * sampleInterval);
+}
+
+//Slew to given ratio.
+//0 : next voice is one fifth  above previous voice.
+//1 : next voice is one octave above previous voice.
+void Synth::setTargetRatio(double in){
+    targetRatio = 1.5 + in * 0.5;
+}
+
+void Synth::setVolume(double in){
+    volume = in;
+}

src/yaw-shepard/synth.h

@@ -0,0 +1,37 @@
+#include "DistrhoPlugin.hpp"
+#include <array>
+
+struct Voice
+{
+    double hz;
+    double phase;
+};
+
+constexpr int NUM_VOICES = 256;
+constexpr uchar VOICE_MASK = 0xFF;
+
+class Synth
+{
+public:
+    explicit Synth(double sampleRate);
+    void process(float *output, uint32_t frames);
+    void setFrequencyShift(double in);
+    void setTargetRatio(double in);
+    void setSampleRate(double oldRate, double newRate);
+    void setVolume(double in);
+
+private:
+    //Phase must persist between run invocation.
+    //Phase of each voice, considered as a period function on the unit interval.
+    std::array<double, NUM_VOICES> phases = {0};
+    //Index of lowest voice in phase array.
+    uchar idxFund = 0;
+    float volume = 0.0f;
+    double hzFund = 32.7;
+    double hzShift = 1.0;
+    double hzNyq = 24000.0;
+    double ratio = 2.0;
+    double targetRatio = 2.0;
+    double ratioSlewRate = 0.99999;
+    double sampleInterval = 1.0 / 48000.0;
+};