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corbanbrook/snippet.js

Created January 13, 2010 16:50
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snippet.js
/* Oscillator Signal Generator
*
* Usage: var sine = Oscillator(SINEWAVE, 440.0, 1, 2048, 44100);
* var signal = sine.generate();
*
*/
SINEWAVE = 1;
SQUAREWAVE = 2;
SAWWAVE = 3;
TRIANGLEWAVE =4;
p.Oscillator = function(_waveform, _frequency, _amplitude, _bufferSize, _sampleRate) {
var waveform = _waveform;
var frequency = _frequency;
var amplitude = _amplitude;
var bufferSize = _bufferSize;
var sampleRate = _sampleRate;
var frameCount = 0;
var frameOffset = frameCount * bufferSize;
var cyclesPerSample = frequency / sampleRate;
var TWO_PI = 2*Math.PI;
var self = {
signal: new Array(bufferSize),
setAmp: function(_amplitude) {
if (_amplitude >= 0 && _amplitude <= 1) {
amplitude = amplitude;
} else {
throw "Amplitude out of range (0..1).";
}
},
setFreq: function(_frequency) {
frequency = _frequency;
cyclesPerSample = frequency / sampleRate;
},
add: function(_oscillator) {
for ( var i = 0; i < bufferSize; i++ ) {
self.signal[i] += _oscillator.valueAt(i);
}
return self.signal;
},
valueAt: function(_offset) {
var value;
var step = _offset * cyclesPerSample % 1;
switch(waveform) {
case SINEWAVE:
value = Math.sin(TWO_PI * step);
break;
case SQUAREWAVE:
value = step < 0.5 ? 1 : -1;
break;
case SAWWAVE:
value = 2 * (step - Math.round(step));
break;
case TRIANGLEWAVE:
value = 1 - 4 * Math.abs(Math.round(step) - step);
break;
}
return value * amplitude;
},
generate: function() {
for ( var i = 0; i < bufferSize; i++ ) {
self.signal[i] = self.valueAt(frameOffset + i);
}
frameCount++;
return self.signal;
}
};
return self;
}
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