Audio Speed & Pitch Modulator
Slow a song down without making it sound underwater. Pitch-shift without changing tempo. Real independent control via a phase vocoder (SoundTouchJS), browser-only, WAV export.
How it works
True independent tempo and pitch control needs a phase vocoder — a fairly heavy DSP algorithm that splits audio into overlapping windows, FFT-shifts the spectrum, and reconstructs. We use SoundTouchJS (a JS port of the popular SoundTouch library) — lazy-loaded from jsdelivr on first export, ~80 kB.
Export pipeline: decode your file via decodeAudioData → push every sample through a SoundTouch SimpleFilter with the chosen tempo + pitch → write the output samples into a fresh AudioBuffer → encode 16-bit PCM WAV.
For long files, processing is chunked through requestAnimationFrame with a live progress bar so the UI stays responsive.