How to use it
- Drop an audio file (or a video for its soundtrack).
- Pick a speed preset or drag the slider.
- Choose Keep pitch or Tape effect, and Reverse if you want.
- Preview, then save as MP3 or WAV.
Keep pitch or tape effect?
Keep pitch changes the tempo without making voices deeper or squeakier. It uses time-stretching: the audio is cut into short overlapping slices that are spaced closer together or further apart. It's ideal for learning a song at a slower tempo, transcribing an interview, or listening to a lecture faster.
Tape effect works like playing a record or tape at the wrong speed: faster means higher pitch (chipmunk voice), slower means lower pitch. That's the classic sound of "sped up" and "slowed + reverb" edits.
| Speed | Keep pitch | Tape effect |
|---|---|---|
| 0.5× | Half tempo, same pitch | One octave lower |
| 0.75× | Slower, same pitch | About 5 semitones lower |
| 1.25× | Faster, same pitch | About 4 semitones higher |
| 2× | Double tempo, same pitch | One octave higher |
Choosing the speed
Click a preset (0.5×, 0.75×, 0.9×, 1×, 1.1×, 1.25×, 1.5× or 2×) or drag the slider in 0.05 steps. The label shows the exact factor and the new length of the file.
- Practicing music: 0.75× or 0.9× with Keep pitch.
- Podcasts and lectures: 1.25×–1.5× with Keep pitch.
- Sped-up or slowed edits: 1.25×–1.5× or 0.75×–0.85× with Tape effect.
- Transcribing: 0.75× with Keep pitch.
Click Preview to hear about 12 seconds of the result before saving.
Reverse audio
Tick Reverse to play the file backwards, alone or combined with a speed change. It's used for sound effects, reverse cymbal swells, music experiments and finding "hidden messages". With reverse on, the preview plays the end of the file.
Saving and quality
Save as MP3 (128, 192 or 320 kbps) or WAV. The file name records what you did, for example song-1_25x.mp3 or song-reversed.mp3. Keep-pitch processing of a long file takes a few seconds; a message shows while it's working.
Time-stretching works best within about 0.75×–1.5×. At the extremes, especially 0.5× with Keep pitch, you may hear a slight echo or phasing; that's normal for this technique.
Privacy
Everything is processed in your browser; the file is never uploaded. You can use any audio format your browser decodes, and the soundtrack of MP4 or MOV videos. To change the speed of a video itself, use a video editor.
Frequently asked questions
How do I slow down a song without changing the pitch?
Choose a speed below 1× (for example 0.75×) and select Keep pitch, then save.
How do I make a sped-up version of a song?
Pick 1.25× or 1.5× and select Tape effect; the pitch rises with the speed, like the popular sped-up edits.
Can I reverse an MP3?
Yes. Tick Reverse, preview, and save; you can combine it with a speed change.
What speeds are possible?
From 0.5× to 2×, in steps of 0.05.
Is my audio uploaded?
No. All processing happens on your device.
Last updated: November 12, 2026