Slow a record down on an old turntable and everything drops: slower and lower, the singer suddenly a baritone. That's because speed and pitch were physically welded together — until time-stretching separated them. Today you can slow a track to 80% to learn the solo, or nudge it +6% to match your set, without moving it a single semitone.
The guitar solo goes by too fast, the vocal run is a blur. At 75-85% speed, in the original key, every note becomes readable — and you're still training your ear in the right key, which half-speed pitch-dropping never did.
Two tracks at 122 and 128 BPM won't blend. Stretch one (or meet in the middle) and the beatmatch locks — keys intact, so your harmonic mixing still works.
The video is 32 seconds, your music bed is 34. A 6% stretch closes the gap invisibly — no cut, no fade trick.
Dancers rehearse at 90%, then 95%, then full speed — same routine, same music, same key, rising tempo.
The audio is cut into tiny overlapping grains, and the algorithm re-spaces them — closer together to speed up, further apart to slow down — while rebuilding the waveform so the pitch stays put. It's honest to say this is signal surgery: the further you stretch, the more the seams can show, especially on drums (transients soften) and reverb tails (a slight watery shimmer).
The practical rule: ±20% is usually transparent, ±30% is workable, beyond that it becomes an effect — sometimes a beautiful one (half-speed ambient stretches are a genre of their own), but an effect.
AudioKit's Time Stretch runs locally — your file never leaves your device:
Time-stretching moves tempo only. If you want to move the key without touching the speed — transpose a backing track for your voice, fix a 432 Hz recording — that's the sister tool: the Pitch Shifter. And if you want the old-turntable effect where both move together, stretch and shift by matching amounts.
Not here — that's the whole point. The key stays identical at any speed.
Depends on the material. Sparse acoustic music tolerates more; dense drums show artifacts first. Stay within ±20% for transparency, and always preview.
Full mixes work fine — that's the main use case. Stems stretch even cleaner if you have them.