Change Audio Speed

Change Audio Speed is a free online tool that speeds up or slows down any audio file. Upload the audio, pick a playback rate between 0.25x and 4x, listen to the result right away and download it as a WAV file. You can keep the original pitch, so only the speed changes, or let the pitch follow the speed like an old tape player does.

Your file is never uploaded anywhere: it is read, played and processed inside your own browser.

How to use this online tool?

1. Upload the audio file you want to speed up or slow down.
2. Move the speed slider, type the exact rate you want, or click one of the shortcuts (0.5x, 1.5x, 2x, ...).
3. Decide whether the audio should keep the original pitch or not.
4. Press play on the audio player to hear the result before saving it.
5. Click "Download" to save the audio with the new speed as a WAV file.

The player gives you the result immediately, while the download is rendered from scratch out of the original samples, so the file you save is a real audio file with the new duration and not a recording of the preview.

What can you use it for?

• Listening to a podcast, a lecture or an audiobook faster, and keeping that speed in the file itself.
• Slowing down a song to learn how to play it, note by note, without the instruments going out of tune.
• Slowing down speech to transcribe it, or to understand a recording in a foreign language.
• Fitting a narration inside a video, by shortening or stretching it by a few percent.
• Creating chipmunk and slow motion voices for videos and games, by turning the pitch lock off.
• Changing the tempo of a loop so it lines up with the rest of a track.

Speed and pitch

Speed and pitch are the same thing to a recording. If you play a tape twice as fast, every wave inside it happens twice as often, so every frequency doubles and the whole recording jumps one octave up. That is what happens when the "keep the original pitch" switch is off: the tool simply resamples the audio, exactly like a turntable spinning faster, and the result gets higher along with faster.

With the switch on, the tool has to be smarter. It cuts the audio into small pieces of about 80 milliseconds and glues them back together closer to each other (to speed it up) or further apart, even repeating a piece here and there (to slow it down). Each wave inside a piece is left untouched, which is why the pitch does not move. The catch is the seams: gluing two pieces at the wrong point produces a click, so before every seam the tool searches for the spot where the two waveforms look the most alike, and crossfades them there. This is known as WSOLA, waveform similarity overlap-add, and it is the same family of algorithms that video players use for their speed controls.

Neither method is magic. Very large changes, and especially very slow speeds, can leave a slight metallic or echoing quality on the pitch corrected audio. Speech and single instruments survive much better than dense mixes, and rates between 0.5x and 2x almost always sound clean.

Which files can I use?

Anything your browser is able to play: MP3, WAV, OGG, M4A, AAC, FLAC, WebM, Opus and so on. The tool decodes the file with your browser's own audio decoder, so the exact list depends on the browser you are using. The result is always saved as a WAV file, which is uncompressed: it keeps the full quality, but it is considerably bigger than an MP3 of the same audio.

Is my audio uploaded to a server?

No. This tool has no server side at all. Your file is read by the browser, decoded by the browser, processed by the browser and saved by the browser. It never leaves your computer, which also means the tool keeps working if you lose your connection after the page has loaded.