Tone.js/Tone/effect/Chebyshev.js

import Tone from "../core/Tone";
import "../effect/Effect";
import "../signal/WaveShaper";

/**
 *  @class Tone.ChebyShev is a Chebyshev waveshaper, an effect which is good 
 *         for making different types of distortion sounds.
 *         Note that odd orders sound very different from even ones, 
 *         and order = 1 is no change. 
 *         Read more at [music.columbia.edu](http://music.columbia.edu/cmc/musicandcomputers/chapter4/04_06.php).
 *
 *  @extends {Tone.Effect}
 *  @constructor
 *  @param {Positive|Object} [order] The order of the chebyshev polynomial. Normal range between 1-100. 
 *  @example
 * //create a new cheby
 * var cheby = new Tone.Chebyshev(50);
 * //create a monosynth connected to our cheby
 * synth = new Tone.MonoSynth().connect(cheby);
 */
Tone.Chebyshev = function(){

	var options = Tone.defaults(arguments, ["order"], Tone.Chebyshev);
	Tone.Effect.call(this, options);

	/**
	 *  @type {WaveShaperNode}
	 *  @private
	 */
	this._shaper = new Tone.WaveShaper(4096);

	/**
	 * holds onto the order of the filter
	 * @type {number}
	 * @private
	 */
	this._order = options.order;

	this.connectEffect(this._shaper);
	this.order = options.order;
	this.oversample = options.oversample;
};

Tone.extend(Tone.Chebyshev, Tone.Effect);

/**
 *  @static
 *  @const
 *  @type {Object}
 */
Tone.Chebyshev.defaults = {
	"order" : 1,
	"oversample" : "none"
};

/**
 *  get the coefficient for that degree
 *  @param {number} x the x value
 *  @param   {number} degree 
 *  @param {Object} memo memoize the computed value. 
 *                       this speeds up computation greatly. 
 *  @return  {number}       the coefficient 
 *  @private
 */
Tone.Chebyshev.prototype._getCoefficient = function(x, degree, memo){
	if (memo.hasOwnProperty(degree)){
		return memo[degree];
	} else if (degree === 0){
		memo[degree] = 0;
	} else if (degree === 1){
		memo[degree] = x;
	} else {
		memo[degree] = 2 * x * this._getCoefficient(x, degree - 1, memo) - this._getCoefficient(x, degree - 2, memo);
	}
	return memo[degree];
};

/**
 * The order of the Chebyshev polynomial which creates
 * the equation which is applied to the incoming 
 * signal through a Tone.WaveShaper. The equations
 * are in the form:<br>
 * order 2: 2x^2 + 1<br>
 * order 3: 4x^3 + 3x <br>
 * @memberOf Tone.Chebyshev#
 * @type {Positive}
 * @name order
 */
Object.defineProperty(Tone.Chebyshev.prototype, "order", {
	get : function(){
		return this._order;
	},
	set : function(order){
		this._order = order;
		var curve = new Array(4096);
		var len = curve.length;
		for (var i = 0; i < len; ++i){
			var x = i * 2 / len - 1;
			if (x === 0){
				//should output 0 when input is 0
				curve[i] = 0;
			} else {
				curve[i] = this._getCoefficient(x, order, {});
			}
		}
		this._shaper.curve = curve;
	} 
});

/**
 * The oversampling of the effect. Can either be "none", "2x" or "4x".
 * @memberOf Tone.Chebyshev#
 * @type {string}
 * @name oversample
 */
Object.defineProperty(Tone.Chebyshev.prototype, "oversample", {
	get : function(){
		return this._shaper.oversample;
	},
	set : function(oversampling){
		this._shaper.oversample = oversampling;
	} 
});

/**
 *  Clean up. 
 *  @returns {Tone.Chebyshev} this
 */
Tone.Chebyshev.prototype.dispose = function(){
	Tone.Effect.prototype.dispose.call(this);
	this._shaper.dispose();
	this._shaper = null;
	return this;
};

export default Tone.Chebyshev;