AudioNode: connect() method

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.

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.

IndexSizeError DOMException

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

InvalidAccessError DOMException

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

NotSupportedError DOMException

Thrown if the specified connection would create a cycle (in which the audio loops back through the same nodes repeatedly) and there are no DelayNode objects in the cycle to prevent the resulting waveform from getting stuck constructing the same audio frame indefinitely. Also thrown if the inputIndex parameter is used while the destination is an AudioParam.

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 HTML 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.

const audioCtx = new AudioContext();

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

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

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.

const audioCtx = new AudioContext();

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

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

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

// create a gain whose gain AudioParam will be controlled by the LFO
const 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.

• Using the Web Audio API