1import { drywet, onceEnded, releaseAudioNode } from './helpers.mjs';
2import { getAudioContext } from './audioContext.mjs';
3
4let noiseCache = {};
5
6// lazy generates noise buffers and keeps them forever
7export function getNoiseBuffer(type, density) {
8  const ac = getAudioContext();
9  if (noiseCache[type]) {
10    return noiseCache[type];
11  }
12  const bufferSize = 2 * ac.sampleRate;
13  const noiseBuffer = ac.createBuffer(1, bufferSize, ac.sampleRate);
14  const output = noiseBuffer.getChannelData(0);
15  let lastOut = 0;
16  let b0, b1, b2, b3, b4, b5, b6;
17  b0 = b1 = b2 = b3 = b4 = b5 = b6 = 0.0;
18
19  for (let i = 0; i < bufferSize; i++) {
20    if (type === 'white') {
21      output[i] = Math.random() * 2 - 1;
22    } else if (type === 'brown') {
23      let white = Math.random() * 2 - 1;
24      output[i] = (lastOut + 0.02 * white) / 1.02;
25      lastOut = output[i];
26    } else if (type === 'pink') {
27      let white = Math.random() * 2 - 1;
28      b0 = 0.99886 * b0 + white * 0.0555179;
29      b1 = 0.99332 * b1 + white * 0.0750759;
30      b2 = 0.969 * b2 + white * 0.153852;
31      b3 = 0.8665 * b3 + white * 0.3104856;
32      b4 = 0.55 * b4 + white * 0.5329522;
33      b5 = -0.7616 * b5 - white * 0.016898;
34      output[i] = b0 + b1 + b2 + b3 + b4 + b5 + b6 + white * 0.5362;
35      output[i] *= 0.11;
36      b6 = white * 0.115926;
37    } else if (type === 'crackle') {
38      const probability = density * 0.01;
39      if (Math.random() < probability) {
40        output[i] = Math.random() * 2 - 1;
41      } else {
42        output[i] = 0;
43      }
44    }
45  }
46
47  // Prevent caching to randomize crackles
48  if (type !== 'crackle') noiseCache[type] = noiseBuffer;
49  return noiseBuffer;
50}
51
52// expects one of noises as type
53export function getNoiseOscillator(type = 'white', t, density = 0.02) {
54  const ac = getAudioContext();
55  const o = ac.createBufferSource();
56  o.buffer = getNoiseBuffer(type, density);
57  o.loop = true;
58  o.start(t);
59  return {
60    node: o,
61    stop: (time) => o.stop(time),
62  };
63}
64
65export function getNoiseMix(inputNode, wet, t) {
66  const noiseOscillator = getNoiseOscillator('pink', t);
67  const noiseMix = drywet(inputNode, noiseOscillator.node, wet);
68  onceEnded(noiseOscillator.node, () => {
69    releaseAudioNode(noiseOscillator.node);
70  });
71  return {
72    node: noiseMix.node,
73    stop: (time) => noiseOscillator?.stop(time),
74    teardown: noiseMix.teardown,
75  };
76}