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About this tool
Work out stretch percentage, new clip length and the pitch shift in semitones and cents when you move audio from one tempo to another.
Tempo Time Stretch Calculator shows what happens to length and pitch when audio recorded at one tempo is played at another. Length scales by the ratio of the two tempos — a 120 BPM loop played at 128 BPM becomes 93.75% of its original duration — and if the change is done by resampling rather than elastic stretching, pitch moves by 12·log2 of the speed ratio, which is 1.117 semitones in that example. It reports the stretch percentage DAWs display, the new clip length, the shift in semitones and cents, and the varispeed sample rate.
Open Tempo Time Stretch Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
One ratio drives both, so you see the trade-off resampling forces on you.
Small tempo moves produce fractional semitones — shown to the cent, not rounded away.
Flags shifts beyond about three semitones, where stretch algorithms usually start to show.
Divide the original tempo by the new tempo and multiply by 100. Going from 120 BPM to 128 BPM gives 120 ÷ 128 = 0.9375, so the audio becomes 93.75% of its original length while playing at 106.67% speed.
If you resample, semitones = 12 × log2(new speed ÷ old speed). Doubling the speed raises pitch by exactly 12 semitones (one octave); a 6.67% speed increase raises it by about 1.12 semitones, or 112 cents.
Yes — elastic time-stretch modes such as Ableton Warp, Logic Flex Time and Pro Tools Elastic Audio decouple length from pitch. They work by resynthesising the signal, so large shifts introduce smearing or a metallic quality even though the key is preserved.
As a working guideline, changes within about ±3 semitones (roughly +19% or −16% speed) hold up on most material, and percussive or single-instrument sources stretch further than dense full mixes. There is no hard threshold — audition the result rather than trusting a number.
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