SoundTouch-TS

A port of a port to TypeScript. Pitchshift and Timestretch in JS/TS. This library is LGPL2.1 due to SoundTouch. A more tested port of this library, with more utilities, is available in soundtouch-js. This TS port exists because I wanted the types, and didn't know soundtouch-js existed until recently.

However, as long as you allow a user, at runtime, to swap out this library, it should fall under section 6b of https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html. But JS/TS and LGPL are legally ambiguous, so use at your own risk.

Usage

// It's TS, but JS is fine too!
import { SoundTouch } from "soundtouch-ts";
const st = new SoundTouch(44100);

const tempo = 0.5;

// Audio will take 2x as long to play with no pitch changes
st.tempo = tempo;

const ctx = new AudioContext();

fetch("http://test-audio.somewhere.mp3")
  .then(res => res.arrayBuffer())
  .then(ab => ctx.decodeAudio(ab))
  .then(ab => {
    const interleaved = asInterleaved(ab);
    st.inputBuffer.putSamples(interleaved);
    st.process();

    const channels = 2;
    const receiver = new Float32Array((channels * ab.length) / tempo);

    const requested = 256;
    let received = 0;
    while (st.outputBuffer.frameCount) {
      const queued = st.frameCount;
      st.process();
      st.outputBuffer.receiveSamples(receiver.subarray(received), requested);
      const remaining = st.outputBuffer.frameCount;
      received = (queued - remaining) * channels;
    }

    const audio = asPlanar(receiver, 44100, 2);
    const abnode = new AudioBufferSourceNode(ctx, { buffer: audio });
    ctx.destination.connect(abnode);
    abnode.start();
  });

function asInterleaved(ab: AudioBuffer): Float32Array {
  const channels = ab.numberOfChannels;
  const output = new Float32Array(channels * ab.length);
  for (let i = 0; i < ab.length; i++) {
    for (let c = 0; c < channels; c++) {
      const chan = ab.getChannelData(c);
      output[i * channels + c] = chan[i];
    }
  }
  return output;
}

function asPlanar(
  buffer: Float32Array,
  sampleRate: number,
  channels: number = 2
): AudioBuffer {
  const channelLength = Math.floor(buffer.length / channels);
  const output = new AudioBuffer({
    numberOfChannels: channels,
    length: channelLength,
    sampleRate: sampleRate
  });

  for (let c = 0; c < channels; c++) {
    const chan = output.getChannelData(c);
    for (let i = 0; i < channelLength; i++) {
      chan[i] = buffer[i * channels + c];
    }
  }

  return output;
}

Publishing

$ npm version [xxx]
$ npx pack build && pushd pkg && npm publish
$ git push origin HEAD --tags

History

This port was modified from the following:

• Original Port (LGPL 2.1): https://github.com/also/soundtouch-js/tree/master/src/js
• Modularized / Expanded (MIT): https://github.com/jakubfiala/soundtouch-js
• Modified and included in a UI (MIT): https://github.com/ZVK/stretcher (http://zackzukowski.com/TAP-audio-player/)
• Converted to TypeScript: src/index.ts.

License

GNU Lesser General Public Library, version 2.1