A Web Audio API example with code mostly taken from http://www.html5rocks.com/en/tutorials/webaudio/intro/ by Boris Smus

audio.js

// original code from http://www.html5rocks.com/en/tutorials/webaudio/intro/
// with thanks to Boris Smus (https://twitter.com/borismus)
define([], function() {

    var context;
    var bufferLoader;
    var BUFFERS_TO_LOAD;
    var BUFFERS = {};
    var SOURCES = {};
    var maxGain = 1;
    var minGain = 0;

    function BufferLoader(context, urlList, callback) {
        this.context = context;
        this.urlList = urlList;
        this.onload = callback;
        this.bufferList = [];
        this.loadCount = 0;
    }

    BufferLoader.prototype.loadBuffer = function(url, index) {
        // Load buffer asynchronously
        var request = new XMLHttpRequest();
        request.open("GET", url, true);
        request.responseType = "arraybuffer";

        var loader = this;

        request.onload = function() {
            // Asynchronously decode the audio file data in request.response
            loader
                .context
                .decodeAudioData(request.response, function(buffer) {
                    if (!buffer) {
                        alert('error decoding file data: ' + url);
                        return;
                    }
                    loader.bufferList[index] = buffer;
                    if (++loader.loadCount == loader.urlList.length)
                        loader.onload(loader.bufferList);
                }, function(error) {
                    console.error('decodeAudioData error', error);
                });
        };

        request.onerror = function() {
            alert('BufferLoader: XHR error');
        };

        request.send();
    };

    BufferLoader.prototype.load = function() {
        for (var i = 0; i < this.urlList.length; ++i)
            this.loadBuffer(this.urlList[i], i);
    };

    // Loads all sound samples into the buffers object.
    function loadBuffers(list, loadedCallback) {
        BUFFERS_TO_LOAD = list;
        // Array-ify
        var names = [];
        var paths = [];
        for (var name in BUFFERS_TO_LOAD) {
            var path = BUFFERS_TO_LOAD[name];
            names.push(name);
            paths.push(path);
        }
        bufferLoader = new BufferLoader(context, paths, function(bufferList) {
            for (var i = 0; i < bufferList.length; i++) {
                var buffer = bufferList[i];
                var name = names[i];
                BUFFERS[name] = buffer;
                SOURCES[name] = createSource(buffer);
            }
            window.setTimeout(function() {
                loadedCallback();
            }, 500);
        });
        bufferLoader.load();
    }

    function startAll(shouldMute) {
        // begin each buffer
        for (var s in SOURCES) {
            var src = SOURCES[s];
            if (shouldMute) {
                src.gainNode.gain.value = minGain;
            }
            src.source.start(0);
        }
    }

    function toggleTrack(track) {
        var src = SOURCES[track];
        if (src) {
            var curGain = src.gainNode.gain.value;
            if (curGain === maxGain) { // mute it
                src.gainNode.gain.value = minGain;
            } else { // max it
                src.gainNode.gain.value = maxGain;
            }
        }
    }

    function createSource(buffer) {
        var source = context.createBufferSource();
        var gainNode = context.createGain ? context.createGain() : context.createGainNode();
        source.buffer = buffer;
        source.loop = true;
        source.connect(gainNode);
        gainNode.connect(context.destination);

        return {
            source: source,
            gainNode: gainNode
        };
    }

    function init(listOfTracks, loadedCallback) {
        try {
            // Fix up prefixing
            window.AudioContext = window.AudioContext || window.webkitAudioContext;
            context = new AudioContext();
        } catch (e) {
            alert("Web Audio API is not supported in this browser");
        }
        loadBuffers(listOfTracks, loadedCallback);
    }

    return {
        init: init,
        startAll: startAll,
        toggleTrack: toggleTrack
    };

});