AudioWorkletNode.parameters - Web APIs 编辑

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.

Syntax

audioWorkletNodeInstance.parameters

Value

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.

Examples

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')
whiteNoiseNode.connect(audioContext.destination)

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)

Specifications

Browser compatibility

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See also

• Web Audio API
• Using the Web Audio API