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;
    }