colornoise/color-noise.js

adds methods to create white brown and pink noise to the AudioContext

function colorNoise(){
    (function(AudioContext) {
        AudioContext.prototype.createWhiteNoise = function(bufferSize) {
            bufferSize = bufferSize || 4096;
            var node = this.createScriptProcessor(bufferSize, 1, 1);
            node.onaudioprocess = function(e) {
                var output = e.outputBuffer.getChannelData(0);
                for (var i = 0; i < bufferSize; i++) {
                    output[i] = Math.random() * 2 - 1;
                }
            };
            return node;
        };

        AudioContext.prototype.createPinkNoise = function(bufferSize) {
            bufferSize = bufferSize || 4096;
            var b0, b1, b2, b3, b4, b5, b6;
            b0 = b1 = b2 = b3 = b4 = b5 = b6 = 0.0;
            var node = this.createScriptProcessor(bufferSize, 1, 1);
            node.onaudioprocess = function(e) {
                var output = e.outputBuffer.getChannelData(0);
                for (var i = 0; i < bufferSize; 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;
                    output[i] = b0 + b1 + b2 + b3 + b4 + b5 + b6 + white * 0.5362;
                    output[i] *= 0.11; // (roughly) compensate for gain
                    b6 = white * 0.115926;
                }
            };
            return node;
        };

        AudioContext.prototype.createBrownNoise = function(bufferSize) {
            bufferSize = bufferSize || 4096;
            var lastOut = 0.0;
            var node = this.createScriptProcessor(bufferSize, 1, 1);
            node.onaudioprocess = function(e) {
                var output = e.outputBuffer.getChannelData(0);
                for (var i = 0; i < bufferSize; i++) {
                    var white = Math.random() * 2 - 1;
                    output[i] = (lastOut + (0.02 * white)) / 1.02;
                    lastOut = output[i];
                    output[i] *= 3.5; // (roughly) compensate for gain
                }
            };
            return node;
        };
    })(window.AudioContext || window.webkitAudioContext);

return new AudioContext;
};

module.exports = colorNoise();