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. As an alternative, you can use theBaseAudioContext.createConstantSource()
factory method; see Creating an AudioNode.
Instance 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.
Events
Inherits events from its parent interface, AudioScheduledSourceNode
.
Note: Some browsers' implementations of these events are part of the AudioScheduledSourceNode
interface.
ended
-
Fired whenever the
ConstantSourceNode
data has stopped playing.
Instance methods
Inherits methods from its parent interface, AudioScheduledSourceNode
.
Note: Some browsers' implementations of these methods are part of the AudioScheduledSourceNode
interface.
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:
js
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.
Specifications
Specification |
---|
Web Audio API # ConstantSourceNode |
Browser compatibility
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