ChannelMergerNode

The ChannelMergerNode interface, often used in conjunction with its opposite, ChannelSplitterNode, reunites different mono inputs into a single output. Each input is used to fill a channel of the output. This is useful for accessing each channels separately, e.g. for performing channel mixing where gain must be separately controlled on each channel.

If ChannelMergerNode has one single output, but as many inputs as there are channels to merge; the number of inputs is defined as a parameter of its constructor and the call to AudioContext.createChannelMerger. In the case that no value is given, it will default to 6.

Using a ChannelMergerNode, it is possible to create outputs with more channels than the rendering hardware is able to process. In that case, when the signal is sent to the AudioContext.listener object, supernumerary channels will be ignored.

Constructor

ChannelMergerNode()

Creates a new ChannelMergerNode object instance.

Properties

No specific property; inherits properties from its parent, AudioNode.

Methods

No specific method; inherits methods from its parent, AudioNode.

Example

The following example shows how you could separate a stereo track (say, a piece of music), and process the left and right channel differently. To use them, you need to use the second and third parameters of the AudioNode.connect(AudioNode) method, which allow you to specify both the index of the channel to connect from and the index of the channel to connect to.

var ac = new AudioContext();
ac.decodeAudioData(someStereoBuffer, function(data) {
 var source = ac.createBufferSource();
 source.buffer = data;
 var splitter = ac.createChannelSplitter(2);
 source.connect(splitter);
 var merger = ac.createChannelMerger(2);

 // Reduce the volume of the left channel only
 var gainNode = ac.createGain();
 gainNode.gain.setValueAtTime(0.5, ac.currentTime);
 splitter.connect(gainNode, 0);

 // Connect the splitter back to the second input of the merger: we
 // effectively swap the channels, here, reversing the stereo image.
 gainNode.connect(merger, 0, 1);
 splitter.connect(merger, 1, 0);

 var dest = ac.createMediaStreamDestination();

 // Because we have used a ChannelMergerNode, we now have a stereo
 // MediaStream we can use to pipe the Web Audio graph to WebRTC,
 // MediaRecorder, etc.
 merger.connect(dest);
});

Specifications

Browser compatibility

See also

• Using the Web Audio API