Audio Speed Changer

How to use

1. Load the song you want to speed up or slow down into the Audio file box.
2. Wait for the small player to appear. That one is your original, not the result.
3. Drag the Speed slider. The readout beside the label tracks it to two decimals, and it moves in 0.05 steps.
4. Or skip the aiming: Slowed sets 0.75x, the middle button sets 1.25x, and Nightcore sets 1.5x.
5. Choose an output format. M4A is the default. WAV and FLAC are lossless and come out several times larger.
6. Press Change speed & download. A progress bar fills while it re-encodes, and Cancel stops it if you picked the wrong number.
7. Play the second player to check it, then press Download. The file keeps its old name with the new extension, so mix.mp3 saves as mix.m4a.

About this tool

Two effects come out of the same control here. Push a track above 1x and it gets faster and higher, which is the nightcore sound. Pull it below 1x and it slows and drops in pitch, which is what a slowed edit means. Both happen because changing audio speed by resampling drags pitch along with it, the way a record played at the wrong rpm does. The slider runs 0.5x to 2x in steps of 0.05, and three preset buttons sit underneath it: 0.75x, 1.25x and 1.5x.

Away from edits, I use it to drag a fast passage down far enough to work out what's being played, and to get through a recorded lecture in less time. Length moves with speed, because resampling is the entire mechanism. A 4-minute track at 0.75x runs about 5 minutes 20, and the same track at 1.5x comes in at 2:40. Pick the output format before you run it. M4A is already selected and is the right answer for most things you'd post.

A 52-minute lecture, listened to in 34:40

Load the recording, drag the slider to 1.50x or tap the right-hand preset, and keep M4A. Fifty-two minutes of speech lands at 34:40, and the progress bar's job is the re-encode, not the math.

The price is pitch: at 1.5x the lecturer squeaks. If that grates over a full hour, step down to 1.25x and the same file runs 41:36 with the voice still recognisably human. Check the second player for thirty seconds before you commit to either number.

Rough edges

• Pitch is welded to speed. There's no time-stretch mode that holds the original key, so a lecture at 1.5x sounds like a chipmunk rather than a fast person.
• The slider stops at 0.5x and 2x. Running the output back through gets you further, but resampling twice compounds the artifacts and it turns ugly fast.
• The resampling is linear interpolation between neighboring samples, which is cheap and quick. On bright material at 0.5x you can sometimes hear that as a fizz on cymbals and sibilance. Fine for a vibe edit. Not what you'd master with.
• The whole file gets one rate; there is no way to speed a single passage from here. Cut the section out with the Audio Cutter, change its speed alone, and join the pieces back afterwards.

Frequently asked questions