How to use
- Choose an audio file.
- Drag Speed (0.5–2×) or click a preset, and drag Pitch to shift by semitones.
- Click Preview first 20 s to check, then Process and download.
Options explained
- Speed without pitch change
- WSOLA time stretching changes the length while keeping the pitch, so voices don't turn into chipmunks or slow down into a drawl.
- Semitones
- Twelve semitones make an octave. Singers usually lower a song by 1 to 3 semitones.
Speed and pitch in numbers
The new length is the old length divided by the speed, so a 60-minute lecture takes 40 minutes at 1.5× and 30 minutes at 2×. At 0.5× it takes 120 minutes.
Pitch is measured in semitones, and each semitone multiplies the frequency by the twelfth root of 2 (about 1.0595):
| Shift | Frequency ratio |
|---|---|
| −12 (one octave down) | 0.500 |
| −2 | 0.891 |
| −1 | 0.944 |
| +1 | 1.059 |
| +2 | 1.122 |
| +12 (one octave up) | 2.000 |
Speed and pitch are set separately, so you can slow a recording to 0.75× without changing the key, or change the key by a few semitones without changing the length.
Frequently asked questions
Why does processing take a while?
Time stretching is computed piece by piece, so a few minutes of audio takes several seconds. It runs in the background and the page stays responsive.
Extreme settings sound odd.
Below about 0.6× or above 1.8×, or pitch changes beyond ±7 semitones, may add a slight echo or warble. That is normal for time stretching.
Are my files uploaded?
No. Everything happens in your browser.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.