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Change audio speed

Speed up, slow down or change the pitch of audio, keeping the other, on your device. Free, with no account or uploads.

Drop audio to speed up or slow down

Faster or slower keeping the pitch, the pitch up or down keeping the length, or both; also backwards, karaoke and the channels swapped. On your device. You can also paste with ⌘V or Ctrl+V.

  • MP3
  • M4A
  • Opus
  • FLAC
  • WAV
  • AIFF
  • MP4
  • MOV
  • WebM

Stays on your device · up to 50 files at once

This page is the Audio editor, opened for changing speed and pitch.

What you can do

  • Trim, fade and change the volumeTo the millisecond, on a waveform you can zoom; every edit can be undone, and your file is never changed.
  • Every common formatMP3, M4A (AAC), Opus, FLAC, WAV and iPhone ringtones, from those and from AIFF, Ogg and the sound of videos.
  • Loudness to a standardMeasured as ITU-R BS.1770 does, normalized to −14 LUFS or another target, with a true-peak limiter so nothing clips.
  • Sound out of videoKept exactly as it is, without being encoded again, whenever the format allows; or converted to the format you choose.
  • Checked before you downloadEvery file written is opened again and listened to: its length, rate and channels are held against what you asked.
  • Many files at onceTags and cover art kept, gapless MP3s, a size limit if you need one, and everything in one ZIP.
  • Nothing is uploadedYour files are read and written in this browser. No account, no limits.

A little help along the way

Follow the steps below. Every option is explained underneath.

  1. Add your filesDrop them, choose them or paste them: MP3, M4A, Opus, FLAC, WAV, AIFF or videos.
  2. Choose the speed1.25 times is chosen for you; 0.5 to 2. Keep the pitch on to keep the notes where they are.
  3. Or the pitchUp or down by up to 12 semitones, keeping the length; or backwards, karaoke and the channels.
  4. Listen and downloadEach file is written in its own format unless you choose another, checked and ready to download.
Every option explained
Speed, keeping the pitch
From 0.5 to 2 times as fast. The sound is rebuilt from short overlapping pieces (WSOLA: 40 ms, each placed where its waveform best matches the one before), so the notes stay where they are. Speech and most music sound natural up to about 1.5 times; much faster or slower, a little flutter can be heard.
Pitch, keeping the length
Up or down by up to 12 semitones (an octave): the sound is stretched by the pitch's ratio and then played faster or slower by it. Voices move with the music, so a large change sounds less natural.
Tape speed
With Keep the pitch off, faster is higher and slower is lower, as a tape or a record plays: the sound is resampled, nothing else is done to it, and nothing above the new top frequency folds back.
Channels
Swap left and right, put one side in both ears, or set the balance. Karaoke takes away what is in the middle of a stereo mix, where the voice often is, keeping the bass under 150 Hz: it is not a real vocal remover, works on some songs only and takes away anything else in the middle too. A mono result has no channels to change, and the page says so.
Backwards
The whole sound, from its end to its start. It is kept while it is written (as blobs the browser may hold on disk), so very long files need room. A joined file is reversed as a whole and gets no chapters.
Same as the file
Keeps the file's own sound as it is, without decoding and encoding it again: AAC goes into an M4A, MP3 stays MP3, Opus and Vorbis go into Ogg, FLAC stays FLAC and plain samples become a WAV. Nothing is lost and it takes a moment. When the rate, the channels or a size limit you chose mean the sound must change, it is encoded again in its own kind; sound that cannot be kept (such as AC-3 from a film) becomes AAC, and the page says so.
MP3
Plays everywhere. Written with LAME at a constant bitrate, with the header that tells players the encoder's delay and padding, so the file is exactly as long as the sound. Below 32 kHz an MP3 holds at most 160 kbit/s.
M4A (AAC) and M4R
Smaller than MP3 for the same quality, and played by every phone and computer. Written with your browser's own AAC encoder, or one that comes with the page when it has none. The encoder's priming is measured and an edit list written, so the sound starts and ends where it should. M4R is the same for an iPhone ringtone, which can be at most 40 seconds long (an alert tone 30).
Opus
The best quality for its size, voice above all. It is always written at 48 kHz. Browsers, Android, VLC and recent Apple devices play it.
FLAC and WAV
Lossless: every sample is kept. FLAC is about half the size of WAV. Choose 16-bit (CD quality), 24-bit, or for WAV 32-bit floating point; FLAC holds at most 24 bits.
Quality
Small, Balanced or High set the bitrate for each format (MP3 96, 192 or 320 kbit/s; AAC 96, 160 or 256; Opus 48, 96 or 160), less for mono. Custom lets you pick the bitrate. These numbers are KeepSimp's own choices.
Sample rate and channels
Keep the file's own, or choose one. When a format cannot hold the rate asked, the nearest it can is used and the page says so. Lossy formats here are mono or stereo, so surround sound is mixed down to stereo for them.
Tags and cover art
Title, artist, album, year, genre and the cover picture go into the new file where its format holds them. Switch it off to write none.
File size limit
MP3, M4A and Opus are written at the highest bitrate that keeps each file under the limit, with room for the container; the page says what it chose. Lossless formats cannot be made to fit a size.
The check
Every file written is opened again and decoded from start to end. Its length, sample rate and channels are held against what was asked, an MP3's size against its bitrate, and a file that came out silent is caught. If something is not as asked, the page says what.
Files the browser cannot read
Some browsers' decoders lack a kind of sound (Safari's lacks FLAC in some places). The page then decodes it with the browser's own player, which plays more kinds, and goes on. AIFF is read by KeepSimp itself. A file nothing here can decode says so.
Privacy
Files are read and written in this browser and never uploaded. There is no account and no limit on how many you convert.
Read the step-by-step guide