timestretcher

Offline time-stretching & pitch-shifting built with Rubber Band

Stretch or pitch-shift an AudioBuffer offline — in a Worker, off the main and audio threads — and get an AudioBuffer back. Play it through a plain AudioBufferSourceNode

• timeRatio — output duration ÷ input duration
• semitones — pitch shift

Usage

import { Timestretcher } from "timestretcher"

await Timestretcher.init();   // load the wasm, spins up the worker

const buf = await ctx.decodeAudioData(await (await fetch('audio.wav')).arrayBuffer());

const out = await Timestretcher.timestretch(buf, { timeRatio: 1.5, semitones: 4 });

new AudioBufferSourceNode(ctx, { buffer: out }).start();

Pick the Rubber Band algorithm:

Timestretcher.timestretch(buf, { engine: 'finer', formant: 'preserved' });

Options: engine, formant, pitchMode, transients, detector, phase, window, smoothing, channels.

The defaults work well enough for me.

Build

Needs the Emscripten SDK

npm run build

License

GPL-2.0-or-later as per rubberband. See LICENSE.