Speed up or slow down playback from 50% to 200%. Pitch is kept natural using a built-in time-stretch algorithm, so a sped-up voice doesn't sound like a chipmunk.
The Audio Tempo & Speed Adjuster makes audio faster or slower. Speed up a lecture to save time, slow a solo down to learn it, fit a voice-over to a clip, or create the pitched-down effect of a slowed vinyl.
With Keep the original pitch on, voices stay natural at any speed thanks to a WSOLA time-stretch; turn it off for the classic tape/vinyl effect where pitch rises and falls with speed.
Pitch-preserving speed uses Waveform-Similarity Overlap-Add (WSOLA, Verhelst & Roelands 1993): the signal is cut into overlapping 40 ms frames, and each new frame is taken from the position — within ±12 ms of the nominal one — that best matches the previous frame’s continuation, found by normalised cross-correlation on a mono mix so both stereo channels move together. Frames are blended with a Hann window whose 50% overlap sums to exactly 1, so level is preserved.
The non-pitch-preserving mode is a resample with an anti-alias filter and cubic interpolation, exactly what turning a turntable faster does.
Listen at 1.25–2× to save time.
Slow a passage to 0.5–0.75× without changing its key.
Squeeze or stretch narration by a few percent.
Slowed-and-reverb or chopped-and-screwed styles.
| Range | 0.25×–3× |
|---|---|
| Method | WSOLA (pitch preserved) or resample (tape style) |
| Frame | 40 ms, 50% overlap, ±12 ms search |
| Stereo | Channels stay phase-aligned |
It has to invent or discard audio. WSOLA picks the best-matching segments so the result sounds natural for speech and most music.
Yes — that is the default.
Quality drops beyond about 2× or below 0.5×.
No — this tool uses an overlap-add time-stretch algorithm to keep pitch natural. For the cleanest results, stay within 50%–200% speed.
Simply changing playback rate (like a tape or turntable) shifts pitch along with speed. This tool decouples the two, which is what most people actually want for spoken word or music practice.
This tool runs entirely in your browser using the Web Audio API. Nothing is uploaded, stored or shared — there is no server to send your file to, so it works offline once the page has loaded.
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