robert@464: /*
robert@464:  * FeedbackOscillator.cpp
robert@464:  *
robert@464:  * Recursive phase-shift oscillator implemented
robert@464:  * on the matrix
robert@464:  *
robert@464:  * Andrew McPherson 2014
robert@464:  */
robert@464: 
robert@464: #include "FeedbackOscillator.h"
robert@464: #include <cstdlib>
robert@464: #include <cmath>
robert@464: 
robert@464: #define COEFF_B0 	0
robert@464: #define COEFF_B1	1
robert@464: #define COEFF_A1	2
robert@464: 
robert@464: FeedbackOscillator::FeedbackOscillator()
robert@464: : wavetable1(0), wavetable2(0)
robert@464: {
robert@464: 
robert@464: }
robert@464: 
robert@464: FeedbackOscillator::~FeedbackOscillator() {
robert@464: 	if(wavetable1 != 0)
robert@464: 		free(wavetable1);
robert@464: 	if(wavetable2 != 0)
robert@464: 		free(wavetable2);
robert@464: 
robert@464: }
robert@464: 
robert@464: // Initialise the settings for the feedback oscillator
robert@464: void FeedbackOscillator::initialise(int maxTableSize, float hpfCutoffFrequency, float matrixSampleRate) {
robert@464: 	wavetableMaxLength = maxTableSize;
robert@464: 	if(wavetable1 != 0)
robert@464: 		free(wavetable1);
robert@464: 	if(wavetable2 != 0)
robert@464: 		free(wavetable2);
robert@464: 
robert@464: 	wavetable1 = (float *)malloc(maxTableSize * sizeof(float));
robert@464: 	wavetable2 = (float *)malloc(maxTableSize * sizeof(float));
robert@464: 
robert@464: 	float omega = tan(M_PI * hpfCutoffFrequency / matrixSampleRate);
robert@464: 	float n = 1.0f / (1.0f + omega);
robert@464: 
robert@464: 	coeffs[COEFF_A1] = (omega - 1.0f) * n;
robert@464: 	coeffs[COEFF_B0] = n;
robert@464: 	coeffs[COEFF_B1] = -n;
robert@464: 
robert@464: 	for(int n = 0; n < maxTableSize; n++)
robert@464: 		wavetable1[n] = wavetable2[n] = 0;
robert@464: 
robert@464: 	wavetableRead = wavetable1;
robert@464: 	wavetableWrite = wavetable2;
robert@464: 	wavetableWritePointer = 0;
robert@464: 	sampleCount = lastTriggerCount = 0;
robert@464: }
robert@464: 
robert@464: // Process one sample and store the output value
robert@464: // Returns true if the wavetable needs rendering
robert@464: int FeedbackOscillator::process(float input, float *output) {
robert@464: 	float outFloat = coeffs[COEFF_B0] * input + coeffs[COEFF_B1] * lastInput - coeffs[COEFF_A1] * lastOutput;
robert@464: 	int requestRenderLength = 0;
robert@464: 
robert@464: 	if(outFloat < -0.5)
robert@464: 		*output = 0;
robert@464: 	else if(outFloat > 0.5)
robert@464: 		*output = 1;
robert@464: 	else
robert@464: 		*output = outFloat + 0.5;
robert@464: 
robert@464: 	if(canTrigger && outFloat > 0 && lastOutput <= 0) {
robert@464: 		triggered = true;
robert@464: 		requestRenderLength = wavetableWritePointer;	// How many samples stored thus far?
robert@464: 		if(requestRenderLength < 4)
robert@464: 			requestRenderLength = 0;	// Ignore anything with fewer than 4 points
robert@464: 
robert@464: 		lastTriggerCount = sampleCount;
robert@464: 		canTrigger = false;
robert@464: 		wavetableWritePointer = 0;
robert@464: 
robert@464: 		// Swap buffers
robert@464: 		float *temp = wavetableWrite;
robert@464: 		wavetableWrite = wavetableRead;
robert@464: 		wavetableRead = temp;
robert@464: 	}
robert@464: 
robert@464: 	if(triggered) {
robert@464: 		wavetableWrite[wavetableWritePointer] = outFloat;
robert@464: 		if(++wavetableWritePointer >= wavetableMaxLength) {
robert@464: 			triggered = false;
robert@464: 			wavetableWritePointer = 0;
robert@464: 		}
robert@464: 	}
robert@464: 
robert@464: 	if(sampleCount - lastTriggerCount > 40)
robert@464: 		canTrigger = true;
robert@464: 
robert@464: 	sampleCount++;
robert@464: 
robert@464: 	lastOutput = outFloat;
robert@464: 	lastInput = input;
robert@464: 
robert@464: 	return requestRenderLength;
robert@464: }