https://playhouse.is/vocoder-envelope-processor.js

1class VocoderEnvelopeProcessor extends AudioWorkletProcessor {
2  constructor() {
3    super();
4    this.envelope = 0;
5    this.attack = 0.01;  // ~0.5ms at 48kHz
6    this.release = 0.02; // ~1ms at 48kHz
7  }
8
9  process(inputs, outputs, parameters) {
10    const input = inputs[0];
11    const output = outputs[0];
12
13    if (!input || !input[0]) return true;
14
15    const inputChannel = input[0];
16    const outputChannel = output[0];
17
18    for (let i = 0; i < inputChannel.length; i++) {
19      const absValue = Math.abs(inputChannel[i]);
20
21      // Envelope follower with fast attack, slightly slower release
22      if (absValue > this.envelope) {
23        this.envelope += this.attack * (absValue - this.envelope);
24      } else {
25        this.envelope += this.release * (absValue - this.envelope);
26      }
27
28      // Output the envelope value (DC signal that represents amplitude)
29      // Boost it significantly so it drives gain parameters audibly
30      outputChannel[i] = this.envelope * 4.0;
31    }
32
33    return true;
34  }
35}
36
37registerProcessor('vocoder-envelope-processor', VocoderEnvelopeProcessor);