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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.

Some implementations of this interface inherit from AudioSourceNode directly, implementing AudioScheduledSourceNode's properties and methods.

Number of inputs 0
Number of outputs 1
Channel count 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();
constantSource.connect(gainNode2.gain);
constantSource.connect(gainNode3.gain);
constantSource.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 API
The definition of 'ConstantSourceNode' in that specification.
Working Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 56.0[1] 52 (52)[2] No support 43[1] ?
Feature Android Webview Chrome Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 56.0[1] 56.0 52.0 (52)[1] No support 43[1] 56.0[1]

[1] Chrome and Opera implement start() and stop() directly on this interface.

[2] ConstantSourceNode was introduced in Firefox 52, based directly on AudioNode. The start(), stop() methods were defined directly on this interface, as was the onended event handler. Starting in Firefox 53, this interface instead inherits from AudioScheduledSourceNode.

See also

Document Tags and Contributors

 Contributors to this page: Sheppy, jpmedley
 Last updated by: Sheppy,