Web Audio API library
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* removed promises and mentions of them from tween functions


Bower helios-audio-mixer

Web Audio Mixer

Javascript audio multi-track mixer library.

The Web Audio API (full feature set) is supported in Chrome 10+, Firefox 25+, Safari 6+, and Edge 12+.



gulp to live compile modules, gulp build for minification.

Unit tests use Mocha and Chai.


  • heliosFrameRunner (not really a dependency, but recommended for managing requestAnimationFrame calls)
  • tween.js for tweening
  • Bowser for detecting browser versions, because Chrome and Firefox had some non-standard implementations.


…to Kevin Ennis for his excellent Mix.js. We based this library on Mix.js when we started working with the web audio API a couple years ago.

How to use

Basic Example

var Mixer = new HeliosAudioMixer();

// call update() using requestAnimationFrame (in this case using HeliosFrameRunner)
frameRunner.add({ id: 'mixer', f: Mixer.update });

Mixer.createTrack('track1', { source: 'path/to/audio/file' });


Mixer.getTrack('track1').tweenGain(0, 1)

Remember to call TWEEN.update() using requestAnimationFrame, or tweens won’t work.

Source Types

Tracks use buffer source by default. Use HTML5 element source for a track by setting the sourceMode option (an out-of-DOM <audio> element will be created), or setting the source option to an existing HTML5 media element instead of a string. The main advantage of HTML5 element source is that audio files can be streamed. The main disadvantage is that

Mixer.createTrack('elementSourceTrack', {
  source: 'path/to/audio/file',
  sourceMode: 'element'

Mixer.createTrack('inDOMelementSourceTrack', {
  source: document.queryselector('audio#elementSourceTrack')

API Reference

Feature Detection

Access/override/whatever through Mixer.detect.

Detect = {
    webAudio:    true | false,
    audioTypes: {
      'mp3': true/false,
      'm4a': true/false,
      'ogg': true/false
    }, // in order of preference
    videoType:  {
      '.webm': true/false,
      '.mp4':  true/false,
      '.ogv':  true/false
    bowser:     bowser.js,
    tween:      <Boolean>,



new HeliosAudioMixer( options )

name default notes
audioTypes [ 'mp3', 'm4a', 'ogg' ] List audio file types in order of preference. The first type available in the current browser will be used.
html5 false Force HTML5 mode.

Mixer Methods

Track Management
  • createTrack( 'name', opts ) see track options below
  • removeTrack( 'name' || track object )
  • getTrack( 'name' ) returns track object
  • getTrack( 'name' ).method() access a single track, chainable
Global Mix Control
  • pause()
  • play()
  • mute()
  • unmute()
  • gain( <0-1> )
  • mix.setLogLvl( <Integer> ) 0 none, 1 minimal, 2 spammy


Track Options

mix.createTrack( 'name', options )

name default notes
source "" Path to audio source (without file extension),
OR media element to use as source,
OR audio blob
gain 1 Initial gain (0-1)
panMode "360" Choose between stereo L/R pan (stereo), 360° pan (360), and full 3D pan (3d)
pan 0 Initial pan
nodes [] array of strings: names of desired audio nodes. See Nodes. Gain and pan nodes are always used.
start 0 start time in seconds
currentTime 0 current time (cached for resuming from pause)
looping false
autoplay true play immediately on load
muted false

Track Methods


track.on('event', callback )

See the event list below. The callback receives the track object as an argument.


track.one('event', function)







Getter/setter for gain, range 0-1.

If you call gain() while a track is muted, the value will be cached and applied upon unmuting.

track.tweenGain(setTo, duration)


There are three panning modes available.

  1. Stereo uses a StereoPannerNode, one axis, left to right.
    track.pan() accepts -1 to 1.
  2. 360 uses a simplified PannerNode.
    track.pan() accepts an angle in degrees, or a string: 'front', 'back', 'left', 'right'
  3. 3d uses a full PannerNode.

track.tweenPan(angle, duration)

Works for Stereo and 360 panning.


currentTime( setTo )

Getter/setter for current time, in seconds.


Get track duration in seconds.

formattedTime( includeDuration )

Transforms: 23"00:23" or "00:23/00:45" 90"01:30" or "01:30/2:00"

Track Events

name when
load audio track is ready to play
loadError source file couldn’t be loaded
remove removeTrack()
ended track reaches the end
pan pan is changed
gain gain is changed
analyse audio analysis data is updated


Web Audio Mixer nodes


FFT using the AnalyserNode. Access analysis data at track.analysis. The raw data is available, as well as averages for lows, mids, highs, and the entire spectrum:

track.getAnalysis() returns:

  raw:    [128, 128, ...],
  average: 128,
  low:     128,
  mid:     128,
  high:    128
var track = Mixer.createTrack('analysisTrack', {
  source: 'file',
  nodes: 'analyse'

track.on('play', function(){
  frameRunner.add('fft', 'everyFrame', fft)

function fft(){
  var data = track.getAnalysis();

HTML5 Mode

Fallback mode for older browsers, and iOS 7. Trying to use Web Audio features like pan will fail gracefully, without errors (return false).


In HTML5 mode, creating a track that already exists will change its source, unlike Web Audio mode where this will return an error. This allows you to circumvent the iOS requirement that media elements can only be played after a user taps 'play'—simply play all your tracks on that first tap. NOTE that you can only play one audio element at a time.

// Create all tracks at the start
Mixer.createTrack('track1', {
    source: 'a_file.mp3'
Mixer.createTrack('track2', {});

// on iOS play button tap
for(var i=0; i < Mixer.tracks.length; i++ ){

// If the track’s already been created, the mixer will swap its source
Mixer.createTrack('track1', {
    source:   'file.mp3',
    autoplay:  true

iOS 7

iOS 6 supports the Web Audio API and it works pretty well. iOS 7 "supports" the Web Audio API, but it’s very unstable. Web apps that worked perfectly on iOS 6 will crash in under a minute on iOS 7. Unfortunately Apple won’t allow alternative web rendering engines, so this library falls back to HTML5 on iOS 7.

iOS 8

iOS 8 actually

iOS Volume Control

iOS does not support volume control for HTML5 audio elements. The reasoning is that the user should be able to control the volume with the OS-level volume control. Apparently in Apple-land nobody could ever possibly want to layer two tracks, or fade anything in or out, ever.