AudioNode

The AudioNode interface serves as a versatile interface for constructing an audio processing graph, representing individual units of audio processing functionality. Each AudioNode is associated with a certain number of audio channels that facilitate the transfer of audio data through processing graph.

We usually represent the channels with the standard abbreviations detailed in the table below:

Name	Number of channels	Channels
Mono	1	0: M - mono
Stereo	2	0: L - left 1: R - right
Quad	4	0: L - left 1: R - right 2: SL - surround left 3: SR - surround right
Stereo	6	0: L - left 1: R - right 2: C - center 3: LFE - subwoofer 4: SL - surround left 5: SR - surround right

Mixing

When node has more then one input or number of inputs channels differs from output up-mixing or down-mixing must be conducted. There are three properties involved in mixing process: channelCount, ChannelCountMode, ChannelInterpretation. Based on them we can obtain output's number of channels and mixing strategy.

Properties

Name	Type	Description
context	BaseAudioContext	Associated context.	Read only
numberOfInputs	number	Integer value representing the number of input connections for the node.	Read only
numberOfOutputs	number	Integer value representing the number of output connections for the node.	Read only
channelCount	number	Integer used to determine how many channels are used when up-mixing or down-mixing node's inputs.	Read only
channelCountMode	ChannelCountMode	Enumerated value that specifies the method by which channels are mixed between the node's inputs and outputs.	Read only
channelInterpretation	ChannelInterpretation	Enumerated value that specifies how input channels are mapped to output channels when number of them is different.	Read only

Examples

Connecting node to node

import { OscillatorNode, GainNode, AudioContext } from 'react-native-audio-api';

function App() {
  const audioContext = new AudioContext();
  const oscillatorNode = audioContext.createOscillator();
  const gainNode = audioContext.createGain();

  gainNode.gain.value = 0.5; //lower volume to 0.5
  oscillatorNode.connect(gainNode);
  gainNode.connect(audioContext.destination);
  oscillatorNode.start(audioContext.currentTime);
}

Connecting node to audio param (LFO-controlled parameter)

import { OscillatorNode, GainNode, AudioContext } from 'react-native-audio-api';

function App() {
  const audioContext = new AudioContext();
  const oscillatorNode = audioContext.createOscillator();
  const lfo = audioContext.createOscillator();
  const gainNode = audioContext.createGain();

  gainNode.gain.value = 0.5; //lower volume to 0.5
  lfo.frequency.value = 2; //low frequency oscillator with 2Hz

  // by default oscillator wave values ranges from -1 to 1
  // connecting lfo to gain param will cause the gain param to oscillate at 2Hz and its value will range from 0.5 - 1 to 0.5 + 1
  // you can modulate amplitude by connecting lfo to another gain that would be responsible for this value
  lfo.connect(gainNode.gain)

  oscillatorNode.connect(gainNode);
  gainNode.connect(audioContext.destination);
  oscillatorNode.start(audioContext.currentTime);
  lfo.start(audioContext.currentTime);
}

Methods

connect

The above method lets you connect one of the node's outputs to a destination.

Parameters	Type	Description
destination	AudioNode or AudioParam	AudioNode or AudioParam to which to connect.

Errors:

Error type	Description
InvalidAccessError	If destination is not part of the same audio context as the node.

Returns undefined.

disconnect

The above method lets you disconnect one or more nodes from the node.

Parameters	Type	Description
destination Optional	AudioNode or AudioParam	AudioNode or AudioParam from which to disconnect.

If no arguments provided node disconnects from all outgoing connections.

Returns undefined.

Remarks

numberOfInputs

• Source nodes are characterized by having a numberOfInputs value of 0.

numberOfOutputs

• Destination nodes are characterized by having a numberOfOutputs value of 0.