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Web Audio API eXtension

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WAAX (Web Audio API eXtension)

JavaScript library for music and audio programming on Chrome (r5)

Please Note!

The newer version of library (r13) will be pushed soon and it will include various enhancements and extra elements: Web MIDI API support, Polymer-powered musical UI widgets, and a couple of impressive examples. If you are interested in the future release, you can checkout the 'dev' branch.

The information below is for the previous revision (r5) and will be deprecated with the release of the newer revision (r13) since it is a major update of library including several fundamental changes. Sorry for your inconvineince!

Quick links

Table of Contents


// creating units
var saw = new WX.Oscil({ type:"sawtooth" }),
    sqr = new WX.Oscil({ type:"square" }),
    lpf = new WX.ModLPF({ cutoff:2500, Q:12 }),
    env = new WX.ADSR({ a:0.001, d:0.002, s:0.3, r:0.1 }),
    vrb = new WX.ConVerb({ source:"ir/hall.wav", mix:0.3 });
// building an audiograph, lpf, env, vrb, WX.DAC);
// connecting units;

WAAX is an experimental JavaScript library built on top of Web Audio API in Chrome. With music creation and production in mind, it is designed to offer the higher level of functionality than basic building blocks of Web Audio API.

The goal of this project is 1) to facilitate experiments and iterations of web-based audio programming and 2) to hide audio-specific chores from web developers who are not familiar with audio programming. This library is designed to be used with other JavaScript APIs available on modern web browsers.

The facade of API is strongly inspired by THREE.js and ChucK: Three.js is one of WebGL JavaScript libraries widely being used for web-based 3D graphics. ChucK is an experimental audio programming language being actively developed and used by computer music communities such as PLOrk(Princeton Laptop Orchestra) and SLOrk(Stanford Laptop Orchestra).

As this library is in early stages of development, it currently demonstrates minimum set of features, however, it will embrace more elements as it grows: ready-made instruments, comprehensive timebase system (in conjunction with Web MIDI API), and musical interconnection between multiple Chrome clients.

FireFox has recently started implementing Web Audio API and it's partially available in the Nightly Build. Safari also has the implementation of Web Audio API but it is slightly outdated compared to the one in Chrome.)


Requirements: Google Chrome 20+ on any platform (Win/OSX/Linux). You can check the availability of the API in different web browsers here.

Adjust your volume setting before clicking. It might be loud!


Creating Units

// creating a sampler and a compressor units
var kick = new WX.Sampler({ source: "kd.wav", basePitch: 60 }),
    comp = new WX.Comp();

Like the node in Web Audio API, WAAX has its own atomic object called unit. It is conceptually identical to the 'unit generator' of other audio programming environments. A unit can be created with initial parameters, or it can be set with default parameters when created with no argument.

Making Connections

// connecting units with .to() method;
// equivalent to the above, comp, WX.DAC);

As shown above, the connection between several WAAX units can be achieved by chaining .to() methods. Alternatively, the method can be used to build an audiograph out of multiple units. WX.DAC is the master output of WAAX system.

// native Web Audio API node
var node = myAudioContext.createGain();
// unit => node
// node => unit

The connection from a WAAX unit to Web Audio API node can be done by .connect() method, which is the same method in Web Audio API, but the connection from a node to a unit should be done manually with ._inlet node from a unit. This enables to use the library in conjunction with plain Web Audio API codes.

Setting Parameters

note: this will be changed in the next revision.

comp.threshold = -12;
comp.ratio = 8.0;
kick.params = { source:"kd2.wav", basePitch:48 };

>>> "kd2.wav"
>>> { source:"kd2.wav", basePitch:48 }

All the parameters of a unit is accessible by simply setting or getting values. Alternatively, passing a javascript object literal with parameters into .params is also possible. Getting available parameters from a unit can be done by printing out .params as well.

Visualization : Example

// creating waveform display with target canvas ID
var wf = new WX.Waveform({ canvas:"CANVAS-ID" });
// connecting compressor unit to waveform visualizer;
// draw waveform

Using a set of units called Analyzers, visualizing waveforms and spectrum can be achieved instantly. The visual content will be automatically resized according to the size of the target canvas DOM element.

Sample-accurate Looping

// playNote function
function playNote(next) {
  adsr.noteOff(next + 1.0);
// looping playNote() infinitely every 3 seconds
var myLoop = new WX.Loop(playNote, 0, 3.0);

Triggering events with super-accurate timing is a quite involved task on the web browsers due to the nature of setTimeout() or setInterval() function. However, the WX.Loop() object provides the sample-accurate looping mechanism. The API for sample-accurate event management is the key objective of this library and it will be expanded to accommodate more complex musical forms. (The detailed description of the scheduling mechanism can be found here.)

GUI : Example

// div for UI panel
var panel = document.getElementById("wx-uipanel");
// a knob
var ka = new WX.UIKnob({
  targetDiv:panel, label:"Attack",
  x:250, y:485, offset: 0.001, scale: 0.5, value: 0.2
// targeting an attack parameter in an ADSR unit
ka.setTargetValue(adsr, "a");

The basic GUI interaction is implemented in the current revision (r5): vertical/horizontal slider, and a knob. WAAX units have "modulation targets" that can be controlled by various modulation sources such as GUI components or even other units simply by putting a single line of code.

Units: Generators, Processors and Analyzers

As WAAX is in early stages of development, there are several components (which are yet to be released publicly) to be incorporated into this library in the near future. I am currently expanding its sonic vocabulary by adding more units to the library. The followings are a basic set of units as the first milestone. A detailed documentation for various units will be available soon.


WX.Oscil WX.Noise WX.Sampler WX.LFO WX.ImpTrain


WX.ADSR WX.ModLPF WX.LPF WX.TwinDelay WX.ConVerb WX.Comp WX.C2


WX.Waveform WX.Spectrum WX.Visualizer


WX.UISliderH WX.UISliderV WX.UIKnob


WX.random2 WX.random2f WX.db2lin WX.lin2db WX.pitch2freq WX.freq2pitch

Contact and License

This project is initiated and managed by hoch(Hongchan Choi) at CCRMA/Stanford University. Please refer LICENSE file (MIT License) for more info.

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