Tempo & Pitch Changer
Slow a track down or speed it up without changing its key, or transpose it without changing its tempo. Both controls work independently, entirely in your browser.
Drop a track to reshape
or choose an audio file
MP3 · WAV · FLAC · AAC · M4A · MP4 · OGG · OPUS · up to 25 MB
Your audio stays on your device
This tool decodes, analyses and exports your track entirely in your browser. The file is never uploaded to our servers, and nothing is stored when you close the tab.
- Free
- No account
- Browser processing
How independent tempo and pitch changes work
In the analogue world speed and pitch are the same control. Play a record faster and everything rises in pitch, because you are physically compressing the waveform in time. Digital audio inherits this: read the samples faster and you get the same effect, which is why an unprocessed speed change makes voices sound like cartoon characters.
Separating the two requires resynthesis. This tool uses WSOLA — waveform similarity overlap-add. It cuts the audio into overlapping windows of around sixty milliseconds, then reassembles them at a different spacing to reach the target duration. Crucially, before writing each window it searches a small range of nearby positions for the one whose waveform best matches what has already been written, and splices there. That alignment is what keeps periodic sounds — a sustained vowel, a bass note, a held chord — from tearing into phase cancellation at every join.
Pitch shifting is then built on top of it. To move a track up two semitones without changing its length, the audio is first resampled so it plays higher and shorter, then time-stretched back out to the original duration. Pitch has moved, tempo has not. Combining both controls simply combines the two ratios.
Practical settings that hold up
Time stretching degrades gracefully rather than suddenly. Between roughly 85% and 120% of the original speed almost nobody can hear that anything has been processed. From 70% to 85% the result is clean enough for practice and for most creative use. Below 60% the artefacts become part of the sound, which is exactly why the slowed-down aesthetic uses them deliberately.
Pitch behaves similarly. Two or three semitones in either direction is transparent on most material. Beyond about five semitones the formants — the resonances that make a voice sound like a particular human throat rather than a synthesised one — move with the pitch, and the voice starts to sound artificial. That is not a bug in this implementation; it is what happens to any pitch shift that does not model formants separately.
- Practice: 70–85% speed, pitch unchanged
- Key matching for a singer: ±2 to 3 semitones, speed unchanged
- DJ tempo matching: adjust speed to the target BPM, leave pitch alone
- Creative slowdown: below 70%, where the artefacts become the point
Working out the speed you need
If you are matching a target tempo, the maths is simple: divide the target BPM by the original BPM. A 128 BPM track that needs to sit at 120 becomes 120 ÷ 128 = 0.9375, so 93.75% speed. If you do not know the original tempo, run the file through the Key & BPM Finder first and bring the number back here.
For key matching the same logic applies in semitones. Count the interval between the source key and the target key — from A minor to C minor is three semitones up — and enter it directly. The Camelot code the analyser reports makes this easier: adjacent numbers on the wheel are a fifth apart, and the letter tells you whether you are in the major or minor ring.
Frequently asked questions
Slowing a tape or a sample rate stretches the waveform, which lowers pitch as a side effect. This tool instead cuts the audio into overlapping short grains, then lays those grains back down at a different spacing. Fewer, wider-spaced grains make the track longer; the grains themselves are unchanged, so the pitch stays where it was.