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Fix audio that plays too fast or too slow

Voices a little high and quick, or low and slow? fix.fm undoes a sample-rate mix-up so speed and pitch come back together. Free, nothing uploaded.

Updated

FX-16 / Wrong speedREADY
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In short

A file plays at the wrong speed when its label says one sample rate but the audio was recorded at another, usually because the app and the interface were set differently: 44.1 kHz audio labelled 48 kHz runs 8.8% fast and a little high. fix.fm rebuilds the file at the real rate, so speed and pitch come back together. On our sample a 9.19 s clip came back to 10 s, the voice back at 119 Hz.

What's happening

A file's label says how many samples make one second. When the label is wrong, every player runs too fast or too slow, and the pitch moves with it. The classic mix-up is OBS or a DAW set to 48 kHz while the interface really records at 44.1 kHz: everything plays 8.8% fast and a little high. Old DV camcorders at 32 kHz, some Zoom exports and cheap USB mics do it too.

To tell, compare the length with the session's, or listen for voices that sound slightly sped up.

In Audacity, Tracks, Resample is not the fix: it keeps the wrong speed. Open the track's menu, choose Rate, pick the real rate, then export.

This page undoes a rate mix-up only. Changing pitch or tempo on purpose is a different job.

FX-16 / Wrong speed sample0:09
The sped-up sample. A voice over a quiet music bed, recorded at 44.1 kHz and labelled 48 kHz, so it plays 8.8% fast.

How far the speed fix goes

A voice playing 8.8% fast sat at 130 Hz and came back to 119 Hz and its full 10 seconds. Music in the same mix-up sat 47 cents off A440, which the check flagged as a likely mix-up; after the fix it sat 1 cent off. Measured on with the samples described in how we test.

The speed fix undoes one thing: a file whose label gives the wrong sample rate, so it plays too fast or too slow with the pitch moved along. The three cases below are a clean reading and a piece of synthesised music given the wrong label in software, so we know exactly how they should sound and can check the fixer puts them back.

FX-16 / How far the speed fix goes7 clips

One clean reading and one piece of synthesised music, given the wrong sample rate label in software, then run through this page's fixer at full amount. Every clip is matched to -23 LUFS. Play the clean reading first, then the fast one: the difference is small but clear side by side.

Clean reading

The reference, at the speed and pitch it was read.

Voice, 8.8% fast

Recorded at 44.1 kHz and labelled 48 kHz. A little quicker and higher, like a sped-up version of the same reader. Easy to miss if you never heard the original.

Voice, after the fix

Back to the reader's own pitch and pace, and back to the full ten seconds.

Music, 8.8% fast

The same mix-up on synthesised music. Every note sits about a quarter tone sharp of normal tuning, which is what the check hears.

Music, after the fix

Back in tune and at its own tempo. The fix followed the check's suggestion, with nothing picked by hand.

Voice, 8.1% slow

Recorded at 48 kHz and labelled 44.1 kHz. Lower and a touch sleepy.

Voice, after the fix

Back to the reader's own pitch and pace, saved at 44.1 kHz like the file it came from.

Public-domain LibriVox voice and music synthesised by fix.fm. The mix-ups are made in software rather than with mismatched gear. So the clean version really is what was there before.

Measured on the fixer's output at full amount
CaseThe checkLengthPitchAgainst the original
Clean readingfine10 s119 Hzn/a
Voice, 8.8% fastfine to fine9.19 s to 10 s130 Hz to 119 Hz-83 dB
Music, 8.8% fastmild to fine9.19 s to 10 s+47 cents to -1 cents-32 dB
Voice, 8.1% slowfine to fine10.88 s to 10 s110 Hz to 118 Hzn/a
The check only ever suggests a mix-up, so it reads fine or mild. Pitch is the voice's median pitch, or for music how far its notes sit from standard A440 tuning, in cents (100 cents is one semitone). Against the original compares the fixed file with the recording at its real speed, sample by sample, away from the first and last 10 ms: lower is closer.

The fast voice played in 9.19 seconds at 130 Hz. With "Playing too fast (48k tagged, 44.1k real)" picked, it came back to 10 seconds at 119 Hz, -83 dB from the original: the same recording, to well under anything you could hear.

The music sat 47 cents sharp, which is what the check listens for, so it suggested the mix-up on its own and the fix followed it. Afterwards the music is 1 cent off in tune. It differs from the original by -32 dB because its noise hits reach above 22 kHz, which a 44.1 kHz recording can't hold; that part was never recorded, so no fix can bring it back.

The slow voice played in 10.88 seconds at 110 Hz and came back to 10 seconds at 118 Hz, still a 44.1 kHz file like the one it came from.

What this does not prove: the check didn't flag either voice. A 9% change keeps a voice among ordinary adult voices, so from the sound alone it can't tell a sped-up reader from one who talks a little high. That's why this page lets you pick the mix-up yourself. The check only speaks up on music, which is tuned to a grid, or on a voice far outside any adult's range. How we test has the pass marks behind the check.

How it works here

  1. 01

    Reads the label

    It checks the sample rate in your file's header against the common mix-ups: 48 and 44.1 kHz, 24 and 22.05 kHz, 48 and 32 kHz. On music it also listens for notes sitting a quarter tone off.

  2. 02

    Plays it at the real rate

    Pick the mix-up, or type the speed it plays at. It rebuilds the file at the real rate, so speed and pitch come back together and the length matches the session again.

  3. 03

    Stays on your computer

    Your file is never uploaded. The speed fix runs in this browser tab.

Questions

Why do voices in my recording sound like chipmunks?

Usually the file says it holds more samples per second than were really recorded, so players run through it too fast and the pitch goes up with the speed. A 44.1 kHz recording labelled 48 kHz is 8.8% fast, a slight chipmunk. 32 kHz labelled 48 kHz is 50% fast, a strong one.

Why is my recording 9% shorter than the session?

That is the 44.1 and 48 kHz mix-up: the audio was recorded at 44.1 kHz but saved as 48 kHz, so it plays in 92% of the time. Pick "Playing too fast (48k tagged, 44.1k real)" here and the length comes back to match.

Will this change the pitch too?

Yes, and that is the point. A rate mix-up moves speed and pitch together, so undoing it puts both back where they were recorded. Voices return to their own pitch and music lands back in tune.

I only want to change the pitch. Can this do that?

No. This page only undoes a sample-rate mix-up, which always moves speed and pitch together. To change one without the other, use a pitch shifter or a time stretcher. tonal.fm, our sister site, has both.

How do I fix the wrong speed in Audacity?

Not with Tracks, Resample: that keeps the wrong speed. Open the track's menu by its name, choose Rate, pick the rate it was really recorded at, then export. fix.fm does the same here without installing anything.

Is my audio uploaded anywhere?

No. The file is read and fixed inside this browser tab and never leaves your computer.

Related fixes

Often turns up with Wrong speed

Working on a song? Fix music checks it for this and every other problem a mix can have, in one pass.