Web/API/ConstantSourceNode

The ConstantSourceNode interface—part of the Web Audio API—represents an audio source (based upon AudioScheduledSourceNode) whose output is single unchanging value. This makes it useful for cases in which you need a constant value coming in from an audio source. In addition, it can be used like a constructible AudioParam by automating the value of its offset or by connecting another node to it; see Controlling multiple parameters with ConstantSourceNode.

A ConstantSourceNode has no inputs and exactly one monaural (one-channel) output. The output's value is always the same as the value of the offset parameter.

Number of inputs	`0`
Number of outputs	`1`

Constructor

ConstantSourceNode(): Creates and returns a new ConstantSourceNode instance, optionally specifying an object which establishes initial values for the object's properties. You can also create a ConstantSourceNode whose properties are initialized to their default values by calling AudioContext.createConstantSource().

Properties

Inherits properties from its parent interface, AudioScheduledSourceNode, and adds the following properties:

offset: An AudioParam which specifies the value that this source continuously outputs. The default value is 1.0.

Event handlers

Inherits event handlers from its parent interface, AudioScheduledSourceNode.

Some browsers' implementations of this event handler are part of the AudioScheduledSourceNode interface.

onended: Fired whenever the ConstantSourceNode data has stopped playing.

Methods

Inherits methods from its parent interface, AudioScheduledSourceNode.

Some browsers' implementations of these methods are part of the AudioScheduledSourceNode interface.

start(): Schedules a sound to playback at an exact time.
stop(): Schedules a sound to stop playback at an exact time.

Example

In the article Controlling multiple parameters with ConstantSourceNode, a ConstantSourceNode is created to allow one slider control to change the gain on two GainNodes. The three nodes are set up like this:

gainNode2 = context.createGain();
gainNode3 = context.createGain();
gainNode2.gain.value = gainNode3.gain.value = 0.5;
volumeSliderControl.value = gainNode2.gain.value;

constantNode = context.createConstantSource();
constantNode.connect(gainNode2.gain);
constantNode.connect(gainNode3.gain);
constantNode.start();

gainNode2.connect(context.destination);
gainNode3.connect(context.destination);

This code starts by creating the gain nodes and setting them and the volume control that will adjust their value all to 0.5. Then the ConstantSourceNode is created by calling AudioContext.createConstantSource(), and the gain parameters of each of the two gain nodes are connected to the ConstantSourceNode. After starting the constant source by calling its start() method. Finally, the two gain nodes are connected to the audio destination (typically speakers or headphones).

Now, whenever the value of constantNode.offset changes, the gain on both gainNode2 and gainNode3 will change to have that same value.

To see this example in action, as well as to read the rest of the code from which these snippets were derived, see Controlling multiple parameters with ConstantSourceNode.

Specification

Specification	Status	Comment
Web Audio APIThe definition of 'ConstantSourceNode' in that specification.	Working Draft

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`ConstantSourceNode`	Chrome Full support 56	Edge Full support ≤79	Firefox Full support 52 Notes' Full support 52 Notes' Notes' `ConstantSourceNode` inherited from `AudioNode` initially, but was changed in Firefox 53 to inherit from `AudioScheduledSourceNode`.	IE No support No	Opera Full support 43	Safari No support No	WebView Android Full support 56	Chrome Android Full support 56	Firefox Android Full support 52 Notes' Full support 52 Notes' Notes' `ConstantSourceNode` inherited from `AudioNode` initially, but was changed in Firefox 53 to inherit from `AudioScheduledSourceNode`.	Opera Android Full support 43	Safari iOS No support No	Samsung Internet Android Full support 6.0
`ConstantSourceNode()` constructor	Chrome Full support 56	Edge Full support ≤79	Firefox Full support 52	IE No support No	Opera Full support 43	Safari No support No	WebView Android Full support 56	Chrome Android Full support 56	Firefox Android Full support 52	Opera Android Full support 43	Safari iOS No support No	Samsung Internet Android Full support 6.0
`offset`	Chrome Full support 56	Edge Full support 79	Firefox No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	IE No support No	Opera No support No	Safari No support No	WebView Android No support No	Chrome Android No support No	Firefox Android No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No
`onended`	Chrome Full support 56	Edge Full support 79	Firefox No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	IE No support No	Opera No support No	Safari No support No	WebView Android Full support 56	Chrome Android Full support 56	Firefox Android No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	Opera Android No support No	Safari iOS No support No	Samsung Internet Android Full support 6.0
`start`	Chrome Full support 56	Edge Full support 79	Firefox No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	IE No support No	Opera No support No	Safari No support No	WebView Android Full support 56	Chrome Android Full support 56	Firefox Android No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	Opera Android No support No	Safari iOS No support No	Samsung Internet Android Full support 6.0
`stop`	Chrome Full support 56	Edge Full support 79	Firefox No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	IE No support No	Opera No support No	Safari No support No	WebView Android Full support 56	Chrome Android Full support 56	Firefox Android No support 52 — 53 Notes' No support 52 — 53 Notes' Notes' This property is still available, but via the inheritance of `AudioScheduledSourceNode`.	Opera Android No support No	Safari iOS No support No	Samsung Internet Android Full support 6.0

Legend

Full support: Full support
No support: No support
See implementation notes.': See implementation notes.