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 aConstantSourceNode
whose properties are initialized to their default values by callingAudioContext.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 GainNode
s. 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
.