The read-only parameters property of the AudioWorkletNode interface returns the associated AudioParamMap — that is, a Map-like collection of AudioParam objects. They are instantiated during creation of the underlying AudioWorkletProcessor according to its parameterDescriptors static getter.




The AudioParamMap object containing AudioParam instances. They can be automated in the same way as with default AudioNodes, and their calculated values can be used in the process method of your AudioWorkletProcessor.


To demonstrate creation and usage of custom AudioParams, we'll expand the example from AudioWorkletNode page. There we've created a simple node which outputs white noise. Here, additionally, we'll create a custom gain parameter, so we can directly change volume of the output (although you could use GainNode to achieve this as well).

First, we need to define a custom AudioWorkletProcessor, and register it. Note that this should be done in a separate file.

We expand the processor by adding a static parameterDescriptors getter. It will be used internally by the AudioWorkletNode constructor to populate its parameters with instantiated AudioParam objects.

// white-noise-processor.js
class WhiteNoiseProcessor extends AudioWorkletProcessor {
  static get parameterDescriptors () {
    return [{
      name: 'customGain',
      defaultValue: 1,
      minValue: 0,
      maxValue: 1,
      automationRate: 'a-rate'

  process (inputs, outputs, parameters) {
    const output = outputs[0]
    output.forEach(channel => {
      for (let i = 0; i < channel.length; i++) {
        channel[i] = (Math.random() * 2 - 1) *
          (parameters['customGain'].length > 1 ? parameters['customGain'][i] : parameters['customGain'][0])
        // note: a parameter contains an array of 128 values (one value for each of 128 samples),
        // however it may contain a single value which is to be used for all 128 samples
        // if no automation is scheduled for the moment.
    return true

registerProcessor('white-noise-processor', WhiteNoiseProcessor)

Next, in our main scripts file we'll load the processor, create an instance of AudioWorkletNode passing it the name of the processor, and connect the node to an audio graph.

const audioContext = new AudioContext()
await audioContext.audioWorklet.addModule('white-noise-processor.js')
const whiteNoiseNode = new AudioWorkletNode(audioContext, 'white-noise-processor')

Now we can change the gain on the node like this:

const gainParam = whiteNoiseNode.parameters.get('customGain')
gainParam.setValueAtTime(0, audioContext.currentTime)
gainParam.linearRampToValueAtTime(0.5, audioContext.currentTime + 0.5)


Specification Status Comment
Web Audio API
The definition of 'parameters' in that specification.
Working Draft

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
parametersChrome Full support 66Edge Full support 79Firefox Full support 76IE No support NoOpera Full support YesSafari No support NoWebView Android Full support 66Chrome Android Full support 66Firefox Android No support NoOpera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support 9.0


Full support
Full support
No support
No support

See also