andrewm@0: /*
andrewm@0:  * FeedbackOscillator.cpp
andrewm@0:  *
andrewm@0:  * Recursive phase-shift oscillator implemented
andrewm@0:  * on the matrix
andrewm@0:  *
andrewm@0:  * Andrew McPherson 2014
andrewm@0:  */
andrewm@0: 
andrewm@0: #include "FeedbackOscillator.h"
andrewm@0: #include <cstdlib>
andrewm@0: #include <cmath>
andrewm@0: 
andrewm@0: #define COEFF_B0 	0
andrewm@0: #define COEFF_B1	1
andrewm@0: #define COEFF_A1	2
andrewm@0: 
andrewm@0: FeedbackOscillator::FeedbackOscillator()
andrewm@0: : wavetable1(0), wavetable2(0)
andrewm@0: {
andrewm@0: 
andrewm@0: }
andrewm@0: 
andrewm@0: FeedbackOscillator::~FeedbackOscillator() {
andrewm@0: 	if(wavetable1 != 0)
andrewm@0: 		free(wavetable1);
andrewm@0: 	if(wavetable2 != 0)
andrewm@0: 		free(wavetable2);
andrewm@0: 
andrewm@0: }
andrewm@0: 
andrewm@0: // Initialise the settings for the feedback oscillator
andrewm@0: void FeedbackOscillator::initialise(int maxTableSize, float hpfCutoffFrequency, float matrixSampleRate) {
andrewm@0: 	wavetableMaxLength = maxTableSize;
andrewm@0: 	if(wavetable1 != 0)
andrewm@0: 		free(wavetable1);
andrewm@0: 	if(wavetable2 != 0)
andrewm@0: 		free(wavetable2);
andrewm@0: 
andrewm@0: 	wavetable1 = (float *)malloc(maxTableSize * sizeof(float));
andrewm@0: 	wavetable2 = (float *)malloc(maxTableSize * sizeof(float));
andrewm@0: 
andrewm@0: 	float omega = tan(M_PI * hpfCutoffFrequency / matrixSampleRate);
andrewm@0: 	float n = 1.0f / (1.0f + omega);
andrewm@0: 
andrewm@0: 	coeffs[COEFF_A1] = (omega - 1.0f) * n;
andrewm@0: 	coeffs[COEFF_B0] = n;
andrewm@0: 	coeffs[COEFF_B1] = -n;
andrewm@0: 
andrewm@0: 	for(int n = 0; n < maxTableSize; n++)
andrewm@0: 		wavetable1[n] = wavetable2[n] = 0;
andrewm@0: 
andrewm@0: 	wavetableRead = wavetable1;
andrewm@0: 	wavetableWrite = wavetable2;
andrewm@0: 	wavetableWritePointer = 0;
andrewm@0: 	sampleCount = lastTriggerCount = 0;
andrewm@0: }
andrewm@0: 
andrewm@0: // Process one sample and store the output value
andrewm@0: // Returns true if the wavetable needs rendering
andrewm@50: int FeedbackOscillator::process(float input, float *output) {
andrewm@50: 	float outFloat = coeffs[COEFF_B0] * input + coeffs[COEFF_B1] * lastInput - coeffs[COEFF_A1] * lastOutput;
andrewm@0: 	int requestRenderLength = 0;
andrewm@0: 
andrewm@51: 	if(outFloat < -0.5)
andrewm@51: 		*output = 0;
andrewm@51: 	else if(outFloat > 0.5)
andrewm@51: 		*output = 1;
andrewm@51: 	else
andrewm@51: 		*output = outFloat + 0.5;
andrewm@0: 
andrewm@0: 	if(canTrigger && outFloat > 0 && lastOutput <= 0) {
andrewm@0: 		triggered = true;
andrewm@0: 		requestRenderLength = wavetableWritePointer;	// How many samples stored thus far?
andrewm@0: 		if(requestRenderLength < 4)
andrewm@0: 			requestRenderLength = 0;	// Ignore anything with fewer than 4 points
andrewm@0: 
andrewm@0: 		lastTriggerCount = sampleCount;
andrewm@0: 		canTrigger = false;
andrewm@0: 		wavetableWritePointer = 0;
andrewm@0: 
andrewm@0: 		// Swap buffers
andrewm@0: 		float *temp = wavetableWrite;
andrewm@0: 		wavetableWrite = wavetableRead;
andrewm@0: 		wavetableRead = temp;
andrewm@0: 	}
andrewm@0: 
andrewm@0: 	if(triggered) {
andrewm@0: 		wavetableWrite[wavetableWritePointer] = outFloat;
andrewm@0: 		if(++wavetableWritePointer >= wavetableMaxLength) {
andrewm@0: 			triggered = false;
andrewm@0: 			wavetableWritePointer = 0;
andrewm@0: 		}
andrewm@0: 	}
andrewm@0: 
andrewm@0: 	if(sampleCount - lastTriggerCount > 40)
andrewm@0: 		canTrigger = true;
andrewm@0: 
andrewm@0: 	sampleCount++;
andrewm@0: 
andrewm@0: 	lastOutput = outFloat;
andrewm@50: 	lastInput = input;
andrewm@0: 
andrewm@0: 	return requestRenderLength;
andrewm@0: }