Playing a file faster makes everything rise in pitch, which turns a lecture into a chipmunk. Keeping the pitch means rebuilding the audio at the new length instead: the signal is cut into overlapping grains and laid back down at a different spacing, with each grain shifted slightly to the point where its waveform lines up with what came before. That alignment step is what separates a clean stretch from the warbling, phasey sound of a cheap one. Resampling is still offered, because the tape-speed effect is sometimes exactly what you are after.
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Speed audio up or slow it down while the pitch stays where it was, or resample for the tape-speed effect.
Playing a file faster makes everything rise in pitch, which turns a lecture into a chipmunk. Keeping the pitch means rebuilding the audio at the new length instead: the signal is cut into overlapping grains and laid back down at a different spacing, with each grain shifted slightly to the point where its waveform lines up with what came before. That alignment step is what separates a clean stretch from the warbling, phasey sound of a cheap one. Resampling is still offered, because the tape-speed effect is sometimes exactly what you are after.
The audio is cut into short overlapping grains and reassembled at a different spacing, so the file gets shorter or longer while each grain still contains the original waveform at its original frequency. Before each grain is written, the tool searches a few milliseconds either side for the position where its waveform best matches what is already there, so the pieces join crest to crest instead of fighting each other.
When you want the pitch to move — slowing a recording down to a lower register, or the sped-up tape sound. It is also the exact thing a turntable or tape machine does, so it is the right choice if you are trying to reproduce that.
How long each reassembled piece is. Longer grains hold bass notes together and sound smoother on music; shorter grains follow fast transients better, which suits speech. If a stretch sounds hollow or doubled, try moving it.
Between about 0.7x and 2x most material holds up well. Beyond that the repeated or skipped grains start to be audible, especially on sustained tones — that is a property of the method, not a setting to turn up.
Supported audio content is not uploaded for processing. Reading, stretching, and export run in your browser; site analytics and the assistant are separate.