BrownNoise.js

function BrownNoise(audioContext) {
    this.node = audioContext.createBufferSource();
    var bufferSize = 2 * audioContext.sampleRate,
        buffer = audioContext.createBuffer(1, bufferSize, audioContext.sampleRate),
        data = buffer.getChannelData(0);

    lastOutput = 0;

    for (var i = 0, len = data.length; i < len; i++) {
        var white = Math.random() * 2 - 1;
        data[i] = (lastOutput + white * 0.02) / 1.02;
        lastOutput = data[i];

        data[i] *= 3.5; // Gain
    }

    this.node.buffer = buffer;
    this.node.loop = true
}

var audioContext = new webkitAudioContext(),
    noise = new BrownNoise(audioContext);

noise.node.connect(audioContext.destination);
noise.node.start(0);