Source: source/Noise.js

define(["Tone/core/Tone", "Tone/source/Source"], function(Tone){

	var sampleRate = Tone.context.sampleRate;
	//two seconds per buffer
	var bufferLength = sampleRate * 4;

	/**
	 *  Noise generator. 
	 *
	 *  uses looped noise buffers to save on performance. 
	 *
	 *  @constructor
	 *  @extends {Tone.Source}
	 *  @param {string} type the noise type (white|pink|brown)
	 */
	Tone.Noise = function(type){

		Tone.Source.call(this);

		/**
		 *  @private
		 *  @type {AudioBufferSourceNode}
		 */
		this._source = null;
		
		/**
		 *  the buffer
		 *  @private
		 *  @type {AudioBuffer}
		 */
		this._buffer = null;

		/**
		 *  set a callback function to invoke when the sample is over
		 *  
		 *  @type {function}
		 */
		this.onended = function(){};

		this.setType(this.defaultArg(type, "white"));
	};

	Tone.extend(Tone.Noise, Tone.Source);

	/**
	 *  set the noise type
	 *  
	 *  @param {string} type the noise type (white|pink|brown)
	 *  @param {Tone.Time} time (optional) time that the set will occur
	 */
	Tone.Noise.prototype.setType = function(type, time){
		switch (type){
			case "white" : 
				this._buffer = _whiteNoise;
				break;
			case "pink" : 
				this._buffer = _pinkNoise;
				break;
			case "brown" : 
				this._buffer = _brownNoise;
				break;
			default : 
				this._buffer = _whiteNoise;
		}
		//if it's playing, stop and restart it
		if (this.state === Tone.Source.State.STARTED){
			time = this.toSeconds(time);
			//remove the listener
			this._source.onended = undefined;
			this._stop(time);
			this._start(time);
		}
	};

	/**
	 *  internal start method
	 *  
	 *  @param {Tone.Time} time
	 *  @private
	 */
	Tone.Noise.prototype._start = function(time){		
		this._source = this.context.createBufferSource();
		this._source.buffer = this._buffer;
		this._source.loop = true;
		this._source.start(this.toSeconds(time));
		this.chain(this._source, this.output);
		this._source.onended = this._onended.bind(this);
	};

	/**
	 *  start the noise at a specific time
	 *  
	 *  @param {Tone.Time} time
	 */
	Tone.Noise.prototype.start = function(time){
		if (this.state === Tone.Source.State.STOPPED){
			this.state = Tone.Source.State.STARTED;
			//make the source
			this._start(time);
		}
	};

	/**
	 *  internal stop method
	 *  
	 *  @param {Tone.Time} time
	 *  @private
	 */
	Tone.Noise.prototype._stop = function(time){
		this._source.stop(this.toSeconds(time));
	};


	/**
	 *  stop the noise at a specific time
	 *  
	 *  @param {Tone.Time} time
	 */
	Tone.Noise.prototype.stop = function(time){
		if (this.state === Tone.Source.State.STARTED) {
			if (this._buffer && this._source){
				if (!time){
					this.state = Tone.Source.State.STOPPED;
				}
				this._stop(time);
			}
		}
	};

	/**
	 *  internal call when the buffer is done playing
	 *  
	 *  @private
	 */
	Tone.Noise.prototype._onended = function(){
		this.state = Tone.Source.State.STOPPED;
		this.onended();
	};

	/**
	 *  dispose all the components
	 */
	Tone.Noise.prototype.dispose = function(){
		if (this._source !== null){
			this._source.disconnect();
			this._source = null;
		}
		this._buffer = null;
		this.output.disconnect();
		this.output = null;
	};


	///////////////////////////////////////////////////////////////////////////
	// THE BUFFERS
	// borred heavily from http://noisehack.com/generate-noise-web-audio-api/
	///////////////////////////////////////////////////////////////////////////

	/**
	 *	static brown noise buffer
	 *  
	 *  @static
	 *  @private
	 *  @type {AudioBuffer}
	 */
	var _pinkNoise = (function() {
		var buffer = Tone.context.createBuffer(2, bufferLength, sampleRate);
		for (var channelNum = 0; channelNum < buffer.numberOfChannels; channelNum++){
			var channel = buffer.getChannelData(channelNum);
			var b0, b1, b2, b3, b4, b5, b6;
			b0 = b1 = b2 = b3 = b4 = b5 = b6 = 0.0;
			for (var i = 0; i < bufferLength; i++) {
				var white = Math.random() * 2 - 1;
				b0 = 0.99886 * b0 + white * 0.0555179;
				b1 = 0.99332 * b1 + white * 0.0750759;
				b2 = 0.96900 * b2 + white * 0.1538520;
				b3 = 0.86650 * b3 + white * 0.3104856;
				b4 = 0.55000 * b4 + white * 0.5329522;
				b5 = -0.7616 * b5 - white * 0.0168980;
				channel[i] = b0 + b1 + b2 + b3 + b4 + b5 + b6 + white * 0.5362;
				channel[i] *= 0.11; // (roughly) compensate for gain
				b6 = white * 0.115926;
			}
		}
		return buffer;
	}());

	/**
	 *	static brown noise buffer
	 *  
	 *  @static
	 *  @private
	 *  @type {AudioBuffer}
	 */
	var _brownNoise = (function() {
		var buffer = Tone.context.createBuffer(2, bufferLength, sampleRate);
		for (var channelNum = 0; channelNum < buffer.numberOfChannels; channelNum++){
			var channel = buffer.getChannelData(channelNum);
			var lastOut = 0.0;
			for (var i = 0; i < bufferLength; i++) {
				var white = Math.random() * 2 - 1;
				channel[i] = (lastOut + (0.02 * white)) / 1.02;
				lastOut = channel[i];
				channel[i] *= 3.5; // (roughly) compensate for gain
			}
		}
		return buffer;
	})();

	/**
	 *	static white noise buffer
	 *  
	 *  @static
	 *  @private
	 *  @type {AudioBuffer}
	 */
	var _whiteNoise = (function(){
		var buffer = Tone.context.createBuffer(2, bufferLength, sampleRate);
		for (var channelNum = 0; channelNum < buffer.numberOfChannels; channelNum++){
			var channel = buffer.getChannelData(channelNum);
			for (var i = 0; i < bufferLength; i++){
				channel[i] =  Math.random() * 2 - 1;
			}
		}
		return buffer;
	}());

	return Tone.Noise;
});