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 AudioNode
s, and their calculated values can be used in the process
method of your AudioWorkletProcessor
.
To demonstrate creation and usage of custom AudioParam
s, 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.
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]);
}
});
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);