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Slowing a guitar solo to learn it, listening to a lecture at 1.5×, making a slowed edit of a song: all of these are speed changes, but they call for different handling of pitch. Pick a speed, choose whether the pitch should stay put, preview it and save a new file.
Processing locally on your device
Overview
There are two ways to change speed. Resampling, the classic tape-style method, plays the samples back faster or slower, so pitch moves with tempo: at 2× the audio is an octave higher and at 0.5× an octave lower. Time-stretching changes duration while keeping pitch by rearranging short overlapping slices of the signal. This tool offers both. Change pitch too uses the Web Audio playback rate, so the preview is exactly what you download and the export renders much faster than real time. The sidebar shows the resulting pitch shift in semitones.
Keep pitch uses FFmpeg’s atempo filter, running as WebAssembly in your browser, and reads your original file directly. atempo handles 0.5× to 2× per stage, so larger changes are chained: 4× is two 2× stages and 0.25× is two 0.5× stages. The preview in this mode uses your browser’s own pitch-preserving playback, which sounds very close to the export. The first export downloads the engine (about 31 MB) once; after that it is cached.
Quality depends on how far you go. Speech handles 1.25× to 2× well, and many podcast apps offer steps like 1.2×, 1.5× and 2×. Music is more sensitive: drum hits can smear when stretched heavily, so for practice 0.5× to 0.8× keeps notes clear. Large slow-downs with pitch preserved can sound slightly phasey or metallic.
Changing speed changes length predictably: a 60-minute recording at 1.5× becomes 40 minutes, and at 0.75× it becomes 80 minutes. If you need an exact length, type it into the Fit to a length field and the speed is calculated for you, which helps when audio must fill a 30-second ad or match a video edit.
| Speed | 60-minute file becomes | Pitch with Change pitch too |
|---|---|---|
| 0.5× | 120 min | −12 semitones |
| 0.75× | 80 min | About −5 semitones |
| 0.9× | 66 min 40 s | About −1.8 semitones |
| 1.25× | 48 min | About +3.9 semitones |
| 1.5× | 40 min | About +7 semitones |
| 2× | 30 min | +12 semitones |
Open an audio file or a video.
Drag the speed slider (0.25×–4×), tap a preset, or type a target length.
Choose Keep pitch or Change pitch too.
Preview the result, clicking the waveform to jump around.
Pick a format and click Change speed to download the new file.
Use cases
Slow a fast passage to 0.75× without changing its key, so you can work out the notes on your instrument, then step back up to full speed.
Save a lecture or audiobook chapter at 1.5× to play on a device or car stereo that has no speed control.
Use Change pitch too around 0.8×–0.9× for a slowed version with a deeper tone, or 1.25×–1.3× for a brighter, nightcore-style one.
Make a 32-second voice-over fit a 30-second ad by typing 0:30.00 as the target length; a change of a few percent is barely noticeable.
Pro tips
Answers to common questions about the speed changer.
Yes. Choose Keep pitch: the audio is time-stretched so it plays longer while every note keeps its original pitch.
Doubling the playback rate doubles every frequency in the signal, and doubling a frequency raises it by exactly one octave. Halving the rate lowers it an octave, which is −12 semitones.
The preview uses your browser’s built-in pitch-preserving playback, while the export uses FFmpeg’s atempo filter. Both keep the pitch; small differences in texture can appear at extreme speeds.
Most listeners find up to 1.5× comfortable and up to 2× workable with practice. Beyond 2×, comprehension drops quickly, especially with fast speakers or strong accents.
Change pitch too renders in a moment. Keep pitch runs FFmpeg on your device, which for an hour-long file can take a few minutes depending on your computer.
No. ToolEnhancer processes files on your own device inside the browser. They are never sent to, stored on or seen by our servers.
Yes. The speed changer is free to use with no sign-up, no watermarks and no daily limits.