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Getting Started with Web Audio API

by Mozilla ContributorsApril 22nd, 2020

Too Long; Didn't Read

The Web Audio API is a powerful and versatile system for controlling audio on the Web. It allows developers to choose audio sources, create audio visualizations, create effects to audio, apply spatial effects (such as panning) and much more. We have a simple introductory tutorial for those that are familiar with programming but need a good introduction to some of the terms and structure of the API. It can be used to incorporate audio into your website or application, by providing atmosphere like futurelibrary.no, or auditory feedback on forms.

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The Web Audio API provides a powerful and versatile system for
controlling audio on the Web, allowing developers to choose audio sources, add effects to audio, create audio visualizations, apply
spatial effects (such as panning) and much more.

Web audio concepts and usage

The Web Audio API involves handling audio operations inside an audio context, and has been designed to allow modular routing. Basic audio operations are performed with audio nodes, which are linked together to form an audio routing graph. Several sources — with different types of channel layout — are supported even within a single context. This modular design provides the flexibility to create complex audio functions with dynamic effects.

Audio nodes are linked into chains and simple webs by their inputs and outputs. They typically start with one or more sources. Sources provide arrays of sound intensities (samples) at very small timeslices, often tens of thousands of them per second. These could be either computed mathematically (such as

OscillatorNode

), or they can be recordings from sound/video files (like

AudioBufferSourceNode

and

MediaElementAudioSourceNode

) and audio streams (

MediaStreamAudioSourceNode

In fact, sound files are just recordings of sound intensities themselves, which come in from microphones or electric instruments, and get mixed down into a single, complicated wave.

Outputs of these nodes could be linked to inputs of others, which mix or modify these streams of sound samples into different streams. A common modification is multiplying the samples by a value to make them louder or quieter (as is the case with

GainNode

Once the sound has been sufficiently processed for the intended effect, it can be linked to the input of a destination (

AudioContext.destination

), which sends the sound to the speakers or headphones. This last connection is only necessary if the user is supposed to hear the audio.

A simple, typical workflow for web audio would look something like this:

Create audio context
Inside the context, create sources — such as
```
<audio>
```
, oscillator, stream
Create effects nodes, such as reverb, biquad filter, panner, compressor
Choose final destination of audio, for example your system speakers
Connect the sources up to the effects, and the effects to the destination.

Timing is controlled with high precision and low latency, allowing
developers to write code that responds accurately to events and is able to target specific samples, even at a high sample rate. So applications such as drum machines and sequencers are well within reach.

The Web Audio API also allows us to control how audio is spatialized. Using a system based on a source-listener model, it allows control of the panning model and deals with distance-induced attenuation or doppler shift induced by a moving source (or moving listener).

You can read about the theory of the Web Audio API in a lot more detail in our article Basic concepts behind Web Audio API.

Web Audio API target audience

The Web Audio API can seem intimidating to those that aren't familiar with audio or music terms, and as it incorporates a great deal of functionality it can prove difficult to get started if you are a developer.

It can be used to simply incorporate audio into your website or application, by providing atmosphere like futurelibrary.no, or auditory feedback on forms. However, it can also be used to create advanced interactive instruments. With that in mind, it is suitable for both developers and musicians alike.

We have a simple introductory tutorial for those that are familiar with programming but need a good introduction to some of the terms and structure of the API.

There's also a Basic Concepts Behind Web Audio API article, to help you understand the way digital audio works, specifically in the realm of the API. This also includes a good introduction to some of the concepts the API is built upon.

Learning coding is like playing cards — you learn the rules, then you play, then you go back and learn the rules again, then you play again. So if some of the theory doesn't quite fit after the first tutorial and article, there's an advanced tutorial which extends the first one to help you practise what you've learnt, and apply some more advanced techniques to build up a step sequencer.

We also have other tutorials and comprehensive reference material
available that covers all features of the API. See the sidebar on this
page for more.

If you are more familiar with the musical side of things, are familiar with music theory concepts, want to start building instruments, then you can go ahead and start building things with the advance tutorial and others as a guide (the above linked tutorial covers scheduling notes, creating bespoke oscillators and envelopes, as well as an LFO among other things.)

If you aren't familiar with the programming basics, you might want to consult some beginner's JavaScript tutorials first and then come back here — see our Beginner's JavaScript learning module for a great place to begin.

Web Audio API Interfaces

The Web Audio API has a number of interfaces and associated events,
which we have split up into nine categories of functionality.

General audio graph definition

General containers and definitions that shape audio graphs in Web Audio API usage.

AudioContext

The

AudioContext

interface represents an audio-processing graph built from audio modules linked together, each represented by an

AudioNode

. An audio context controls the creation of the nodes it contains and the execution of the audio processing, or decoding. You need to create an

AudioContext

before you do anything else, as everything happens inside a context.

AudioContextOptions

The

AudioContextOptions

dictionary is used to provide options when instantiating a new

AudioContext

AudioNode

The

AudioNode

interface represents an audio-processing module like an audio source (e.g. an HTML

<audio>

<video>

element), audio destination, intermediate processing module (e.g. a filter like

BiquadFilterNode

, or volume control like

GainNode

AudioParam

The

AudioParam

interface represents an audio-related parameter, like one of an

AudioNode

. It can be set to a specific value or a change in value, and can be scheduled to happen at a specific time and following a specific pattern.

AudioParamMap

Provides a maplike interface to a group of

AudioParam

interfaces, which means it provides the methods

forEach()

get()

has()

keys()

, and

values()

, as well as a

size

property.

BaseAudioContext

The

BaseAudioContext

interface acts as a base definition for online and offline audio-processing graphs, as represented by

AudioContext

and

OfflineAudioContext

respectively. You wouldn't use

BaseAudioContext

directly — you'd use its features via one of these two inheriting interfaces.

The

ended

event

The

ended

event is fired when playback has stopped because the end of the media was reached.

Defining audio sources

Interfaces that define audio sources for use in the Web Audio API.

AudioScheduledSourceNode

The

AudioScheduledSourceNode

is a parent interface for several types of audio source node interfaces. It is an

AudioNode

OscillatorNode

The

OscillatorNode

interface represents a periodic waveform, such as a sine or triangle wave. It is an

AudioNode

audio-processing module that causes a given frequency of wave to be created.

AudioBuffer

The

AudioBuffer

interface represents a short audio asset residing in memory, created from an audio file using the

AudioContext.decodeAudioData()

method, or created with raw data using

AudioContext.createBuffer()

. Once decoded into this form, the audio can then be put into an

AudioBufferSourceNode

AudioBufferSourceNode

The

AudioBufferSourceNode

interface represents an audio source consisting of in-memory audio data, stored in an

AudioBuffer

. It is an

AudioNode

that acts as an audio source.

MediaElementAudioSourceNode

The

MediaElementAudioSourceNode

interface represents an audio source consisting of an HTML5

<audio>

<video>

element. It is an

AudioNode

that acts as an audio source.

MediaStreamAudioSourceNode

The

MediaStreamAudioSourceNode

interface represents an audio source consisting of a

MediaStream

(such as a webcam, microphone, or a stream being sent from a remote computer). If multiple audio tracks are present on the stream, the track whose

id

comes first lexicographically (alphabetically) is used. It is an

AudioNode

that acts as an audio source.

MediaStreamTrackAudioSourceNode

A node of type

MediaStreamTrackAudioSourceNode

represents an audio source whose data comes from a

MediaStreamTrack

. When creating the node using the

createMediaStreamTrackSource()

method to create the node, you specify which track to use. This provides more control than

MediaStreamAudioSourceNode

Defining audio effects filters

Interfaces for defining effects that you want to apply to your audio sources.

BiquadFilterNode

The

BiquadFilterNode

interface represents a simple low-order filter. It is an

AudioNode

that can represent different kinds of filters, tone control devices, or graphic equalizers. A

BiquadFilterNode

always has exactly one input and one output.

ConvolverNode

The

ConvolverNode

interface is an

AudioNode

that performs a Linear Convolution on a given

AudioBuffer

, and is often used to achieve a reverb effect.

DelayNode

The

DelayNode

interface represents a delay-line; an

AudioNode

audio-processing module that causes a delay between the arrival of an input data and its propagation to the output.

DynamicsCompressorNode

The

DynamicsCompressorNode

interface provides a compression effect, which lowers the volume of the loudest parts of the signal in order to help prevent clipping and distortion that can occur when multiple sounds are played and multiplexed together at once.

GainNode

The

GainNode

interface represents a change in volume. It is an

AudioNode

audio-processing module that causes a given gain to be applied to the input data before its propagation to the output.

WaveShaperNode

The

WaveShaperNode

interface represents a non-linear distorter. It is an

AudioNode

that use a curve to apply a waveshaping distortion to the signal. Beside obvious distortion effects, it is often used to add a warm feeling to the signal.

PeriodicWave

Describes a periodic waveform that can be used to shape the output of an OscillatorNode.

IIRFilterNode

Implements a general infinite impulse response (IIR) filter; this type of filter can be used to implement tone control devices and graphic equalizers as well.

Defining audio destinations

Once you are done processing your audio, these interfaces define where to output it.

AudioDestinationNode

The

AudioDestinationNode

interface represents the end destination of an audio source in a given context — usually the speakers of your device.

MediaStreamAudioDestinationNode

The

MediaStreamAudioDestinationNode

interface represents an audio destination consisting of a WebRTC

MediaStream

with a single AudioMediaStreamTrack, which can be used in a similar way to a

MediaStream

obtained from

getUserMedia()

. It is an

AudioNode

that acts as an audio destination.

Data analysis and visualization

If you want to extract time, frequency, and other data from your audio, the AnalyserNode is what you need.

AnalyserNode

The

AnalyserNode

interface represents a node able to provide real-time frequency and time-domain analysis information, for the purposes of data analysis and visualization.

Splitting and merging audio channels

To split and merge audio channels, you'll use these interfaces.

ChannelSplitterNode

The

ChannelSplitterNode

interface separates the different channels of an audio source out into a set of mono outputs.

ChannelMergerNode

The

ChannelMergerNode

interface reunites different mono inputs into a single output. Each input will be used to fill a channel of the output.

Audio spatialization

These interfaces allow you to add audio spatialization panning effects to your audio sources.

AudioListener

The

AudioListener

interface represents the position and orientation of the unique person listening to the audio scene used in audio spatialization.

PannerNode

The

PannerNode

interface represents the position and behavior of an audio source signal in 3D space, allowing you to create complex panning effects.

StereoPannerNode

The

StereoPannerNode

interface represents a simple stereo panner node that can be used to pan an audio stream left or right.

Audio processing in JavaScript

Using audio worklets, you can define custom audio nodes written in JavaScript or WebAssembly. Audio worklets implement the

Worklet

interface, a lightweight version of the

Worker

interface. Audio worklets are enabled by default for Chrome 66 or later.

AudioWorklet

The AudioWorklet interface is available via

BaseAudioContext.audioWorklet

, and allows you to add new modules to the audio worklet.

AudioWorkletNode

The

AudioWorkletNode

interface represents an

AudioNode

that is embedded into an audio graph and can pass messages to the corresponding

AudioWorkletProcessor

AudioWorkletProcessor

The

AudioWorkletProcessor

interface represents audio processing code running in a

AudioWorkletGlobalScope

that generates, processes, or analyses audio directly, and can pass messages to the corresponding

AudioWorkletNode

AudioWorkletGlobalScope

The

AudioWorkletGlobalScope

interface is a

WorkletGlobalScope

-derived object representing a worker context in which an audio processing script is run; it is designed to enable the generation, processing, and analysis of audio data directly using JavaScript in a worklet thread.

Obsolete: script processor nodes

Before audio worklets were defined, the Web Audio API used the

ScriptProcessorNode

for JavaScript-based audio processing. Because the code runs in the main thread, they have bad performance. The

ScriptProcessorNode

is kept for historic reasons but is marked as deprecated and will be removed in a future version of the specification.

ScriptProcessorNode

The ScriptProcessorNode interface allows the generation, processing, or analyzing of audio using JavaScript. It is an

AudioNode

audio-processing module that is linked to two buffers, one containing the current input, one containing the output. An event, implementing the

AudioProcessingEvent

interface, is sent to the object each time the input buffer contains new data, and the event handler terminates when it has filled the output buffer with data.

audioprocess

(event)

The

audioprocess

event is fired when an input buffer of a Web Audio API

ScriptProcessorNode

is ready to be processed.

AudioProcessingEvent

The

Web Audio API

AudioProcessingEvent

represents events that occur when a

ScriptProcessorNode

input buffer is ready to be processed.

Offline/background audio processing

It is possible to process/render an audio graph very quickly in the background — rendering it to an

AudioBuffer

rather than to the device's speakers — with the following.

OfflineAudioContext

The

OfflineAudioContext

interface is an

AudioContext

interface representing an audio-processing graph built from linked together AudioNode
s. In contrast with a standard AudioContext, an OfflineAudioContext doesn't really render the audio but rather generates it, as fast as it can, in a buffer.