comparison examples/10-Instruments/airharp/Waveguide.cpp @ 468:85cf9c0da052 prerelease

merge

+/*
+ *
+ * Simple 1-Dimensional Waveguide
+ *
+ */
+
+#include "Waveguide.h"
+#include "../include/Utilities.h"
+#include <rtdk.h>
+#include <cmath>
+#include <stdio.h>
+#include <cstdlib>
+
+#define DECAY 0.995//0.999
+#define DAMPING 0.01//0.05
+
+// TODO: make damping and decay parametrisable
+
+Waveguide::Waveguide()	{
+
+	// initialize variables
+	a1_lp = 0;
+	a2_lp = 0;
+	b0_lp = 0;
+	b1_lp = 0;
+	b2_lp = 0;
+	_dt = 1.0/44100.0;
+	setFrequency(440);
+	updateFilterCoeffs(8000);
+	_filterReadPtr=0;
+	for(int i=0;i<FILTER_BUFFER_SIZE;i++)	{
+		_filterBuffer_x[i] = 0;
+		_filterBuffer_y[i] = 0;
+	}
+	for(int i=0;i<WG_BUFFER_SIZE;i++)	{
+		_buffer[i] = 0;
+	}
+	_lastX = 0;
+	_lastY = 0;
+	_readPtr = 0;
+
+}
+
+void Waveguide::setup()	{
+
+}
+
+float Waveguide::update(float in)	{
+
+	// 1. advance delay buffer read pointer
+
+	if(++_readPtr>=WG_BUFFER_SIZE)
+		_readPtr=0;
+
+	// 2. write input into buffer
+
+	_buffer[_readPtr] = in;
+
+	// 3. read delayed sample from buffer
+
+	float out = _buffer[(_readPtr-_periodInSamples+WG_BUFFER_SIZE)%WG_BUFFER_SIZE];
+
+	// 4. apply damping (low-pass) filter to output
+
+	if(++_filterReadPtr>=FILTER_BUFFER_SIZE)
+			_filterReadPtr=0;
+
+	out = b0_lp*out +
+					b1_lp*_filterBuffer_x[(_filterReadPtr-1+FILTER_BUFFER_SIZE)%FILTER_BUFFER_SIZE] +
+					b2_lp*_filterBuffer_x[(_filterReadPtr-2+FILTER_BUFFER_SIZE)%FILTER_BUFFER_SIZE] -
+					a1_lp*_filterBuffer_y[(_filterReadPtr-1+FILTER_BUFFER_SIZE)%FILTER_BUFFER_SIZE] -
+					a2_lp*_filterBuffer_y[(_filterReadPtr-2+FILTER_BUFFER_SIZE)%FILTER_BUFFER_SIZE];
+
+	// 5. Simple high-pass filter to block DC-offset
+	// y[n] = x[n] - x[n-1] + a * y[n-1]
+	float gain = 0.9999;
+	float temp = out;
+	out = out - _lastX + gain * _lastY;
+	_lastY = out;
+	_lastX = temp;
+
+	// 6. Apply intensity damping
+	out *= DECAY;
+
+	_filterBuffer_x[_filterReadPtr] = in;
+	_filterBuffer_y[_filterReadPtr] = out;
+
+	return out;
+
+}
+
+void Waveguide::setFrequency(float frequency)	{
+
+	// NB: currently no interpolation, so may not be ideal for dynamically changing waveguide frequency
+	_periodInMilliseconds = 1000.0/frequency;
+	_periodInSamples = (int)(_periodInMilliseconds * 44.1);
+
+}
+
+void Waveguide::updateFilterCoeffs(float frequency)	{
+
+	// FIXME: Butterworth filter doesn't work very well,
+	//		  using simple FIR in the meantime
+
+	a1_lp = 0;
+	a2_lp = 0;
+	b0_lp = 1.0 - DAMPING;
+	b1_lp = DAMPING;
+	b2_lp = 0;
+
+	/*
+	// 'w' for sake of resembling lower-case 'omega'
+	float w = 2.0 * M_PI * frequency;
+	float t = _dt;
+	// The Q for a 2nd-order Butterworth is sqrt(2)/2
+	float q = 0.707;//sqrt(2.0)/2.0;
+
+	// low-pass filter coefficients
+	float a0_lp = w*w*t*t + 2*(w/q)*t + 4.0;
+	float k = 1.0/a0_lp;
+	a1_lp = (2.0*w*w*t*t - 8.0) * k;
+	a2_lp = (4.0 - (w/q)*2.0*t + w*w*t*t) * k;
+	b0_lp = (w*w*t*t) * k;
+	b1_lp = (2.0*w*w*t*t) * k;
+	b2_lp = (w*w*t*t) * k;
+	*/
+
+}