AudioNode.connect() - Web APIs 编辑

The connect() method of the AudioNode interface lets you connect one of the node's outputs to a target, which may be either another AudioNode (thereby directing the sound data to the specified node) or an AudioParam, so that the node's output data is automatically used to change the value of that parameter over time.

Syntax

var destinationNode = AudioNode.connect(destination, outputIndex, inputIndex);

AudioNode.connect(destination, outputIndex);

Parameters

destination

The AudioNode or AudioParam to which to connect.

outputIndex Optional

An index specifying which output of the current AudioNode to connect to the destination. The index numbers are defined according to the number of output channels (see Audio channels). While you can only connect a given output to a given input once (repeated attempts are ignored), you can connect an output to multiple inputs by calling connect() repeatedly. This makes fan-out possible. The default value is 0.

inputIndex Optional

An index describing which input of the destination you want to connect the current AudioNode to; the default is 0. The index numbers are defined according to the number of input channels (see Audio channels). It is possible to connect an AudioNode to another AudioNode, which in turn connects back to the first AudioNode, creating a cycle. This is allowed only if there is at least one DelayNode in the cycle. Otherwise, a NotSupportedError exception is thrown. This parameter is not allowed if the destination is an AudioParam.

Return value

If the destination is a node, connect() returns a reference to the destination AudioNode object, allowing you to chain multiple connect() calls. In some browsers, older implementations of this interface return undefined.

If the destination is an AudioParam, connect() returns undefined.

Exceptions

IndexSizeError

The value specified as outputIndex or inputIndex doesn't correspond to an existing input or output.

InvalidAccessError

The destination node is not part of the same audio context as the source node.

NotSupportedError

The specified connection would create a cycle (in which the audio loops back through the same nodes repeatedly) and there are no DelayNodes in the cycle to prevent the resulting waveform from getting stuck constructing the same audio frame indefinitely.

Examples

Connecting to an audio input

The most obvious use of the connect() method is to direct the audio output from one node into the audio input of another node for further processing. For example, you might send the audio from a MediaElementAudioSourceNode—that is, the audio from an HTML5 media element such as <audio>—through a band pass filter implemented using a BiquadFilterNode to reduce noise before then sending the audio along to the speakers.

This example creates an oscillator, then links it to a gain node, so that the gain node controls the volume of the oscillator node.

var AudioContext = window.AudioContext || window.webkitAudioContext;

var audioCtx = new AudioContext();

var oscillator = audioCtx.createOscillator();
var gainNode = audioCtx.createGain();

oscillator.connect(gainNode);
gainNode.connect(audioCtx.destination);

AudioParam example

In this example, we will be altering the gain value of a GainNode using an OscillatorNode with a slow frequency value. This technique is know as an LFO-controlled parameter.

var AudioContext = window.AudioContext || window.webkitAudioContext;

var audioCtx = new AudioContext();

// create an normal oscillator to make sound
var oscillator = audioCtx.createOscillator();

// create a second oscillator that will be used as an LFO (Low-frequency
// oscillator), and will control a parameter
var lfo = audioCtx.createOscillator();

// set the frequency of the second oscillator to a low number
lfo.frequency.value = 2.0; // 2Hz: two oscillations par second

// create a gain whose gain AudioParam will be controlled by the LFO
var gain = audioCtx.createGain();

// connect the LFO to the gain AudioParam. This means the value of the LFO
// will not produce any audio, but will change the value of the gain instead
lfo.connect(gain.gain);

// connect the oscillator that will produce audio to the gain
oscillator.connect(gain);

// connect the gain to the destination so we hear sound
gain.connect(audioCtx.destination);

// start the oscillator that will produce audio
oscillator.start();

// start the oscillator that will modify the gain value
lfo.start();

AudioParam notes

It is possible to connect an AudioNode output to more than one AudioParam, and more than one AudioNode output to a single AudioParam, with multiple calls to connect(). Fan-in and fan-out are therefore supported.

An AudioParam will take the rendered audio data from any AudioNode output connected to it and convert it to mono by down-mixing (if it is not already mono). Next, it will mix it together with any other such outputs, and the intrinsic parameter value (the value the AudioParam would normally have without any audio connections), including any timeline changes scheduled for the parameter.

Therefore, it is possible to choose the range in which an AudioParam will change by setting the value of the AudioParam to the central frequency, and to use a GainNode between the audio source and the AudioParam to adjust the range of the AudioParam changes.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using the Web Audio API