No upload, 100% local, no account

Change audio speed, keep the pitch

Speed up a podcast or slow down a song without the chipmunk effect, pitch is preserved. Everything runs in your browser; your file never leaves your device.

How Audio speed works

Audio speed lets you change the playback rate of a track from 0.25x to 4x while keeping the original pitch intact, so voices stay natural rather than turning chipmunk-like or unnaturally deep. Speed up a lecture or podcast to save time, or slow a song to 0.5x to transcribe a fast guitar run or learn a language phrase by phrase.

The speed change is done by ffmpeg compiled to WebAssembly, using the atempo filter with automatic chaining when the target falls outside the 0.5x-2x range that atempo handles in a single stage. Pitch is preserved at every step through time-stretching, entirely inside your browser tab; the file is never uploaded. No account, no watermark.

Written by Bastien Sulyan

How to use Audio speed, step by step

  1. Drop or select your audio file (MP3, WAV, M4A, AAC, OGG, FLAC).
  2. Set the playback speed using the slider or type a value between 0.25x and 4x.
  3. Click Change Speed. ffmpeg processes the file locally.
  4. When the progress bar finishes, click Download to save the new file.

Common use cases

  • Speeding up a two-hour lecture to 1.5x or 2x to get through it in less time.
  • Slowing down a music track to 0.5x to learn a difficult chord progression or bass line by ear.
  • Adjusting the pace of a podcast episode for a commute or workout.
  • Preparing an audio clip to match a specific video duration without re-recording it.

Frequently asked questions

Does my audio file get uploaded to change the speed?

No. ffmpeg compiled to WebAssembly changes the speed in your browser tab. Your file is read into memory on your device, the atempo filter runs there, and the result is offered as a local download. Nothing is transmitted to Sunasty or any third party. Open your browser DevTools, go to the Network tab, and trigger the speed change: you will see no outbound request carrying your audio.

Does changing the speed also change the pitch?

No. The atempo filter uses time-stretching to alter duration without affecting frequency content, so pitch is preserved. A sped-up voice sounds faster but not higher-pitched, and a slowed-down voice sounds slower but not lower-pitched. If you want to shift pitch independently (a tape-speed effect that changes both), you would need a different tool.

Why does atempo need to be chained for speeds above 2x or below 0.5x?

The atempo filter accepts input values only in the range 0.5 to 2 per stage. To reach a speed of 4x, the tool chains two stages (2x followed by another 2x). For 0.25x it chains two 0.5x stages. This chaining is handled automatically; you just pick a value from 0.25x to 4x and the tool figures out the chain.

Does the output keep the same audio format as the input?

Yes. The file is processed and returned in the same container and codec as the input. An MP3 in means an MP3 out; a WAV stays a WAV. There is one re-encode pass for the speed change, but the format is preserved.

Can I preview the result before downloading?

A playback button appears once the processing is complete so you can listen before committing to the download. If the speed is not right, adjust the slider and run it again, the source file is still in memory.

Does audio speed work offline?

Mostly. The atempo filter always runs on your device, your audio never leaves your machine. The one caveat is that the ffmpeg engine is a sizeable download fetched from this site the first time you run the tool; once that download and the page have both completed, you can disconnect from the internet and the speed change will still complete normally.