Free audio speed changer, no upload.
A free audio speed changer that slows down or speeds up audio without uploading it — and without turning the speaker into a chipmunk. Pitch is preserved by default, so a voice message slowed to 0.75× still sounds like the person who sent it. Turn that off and you get the old tape-speed effect instead, if that is what you actually want.
Add the audio you want to slow down or speed up
Drag a file here, or press the button. A voice message, a lecture, an interview — anything your browser can play. It stays on this device.
MP3 · M4A · WAV · FLAC · Ogg · Opus · MP4 · MOV — even old AMR and WMA files. You can also paste one from the clipboard.
Your privacy — live proof, not a promise
- Files uploaded
- 0 bytes
- Processing
- Not started yet
- Your files
- Stay in this browser tab — gone when it closes
- Converter engine
- Not downloaded — only fetched if a format needs it
One download, and it isn’t your audio
Converting to MP3 or WAV needs no download at all. Less common formats use a built-in converter engine (32.5 MB) that comes from this site — not from some other company — downloads once, and is then saved in your browser. Your audio is never part of that download: the engine comes to your files, your files don’t go to it.
Don’t take our word for it: open your browser’s DevTools, watch the Network tab, then convert a file. You’ll see nothing carrying your audio — because this page has no upload feature at all. There is nowhere for your file to go.
Scope note, so this stays exact: the claim is about your files — they never leave this device. The site around it is not claim-free. It loads Vercel Analytics for aggregate page traffic, plus Google Analytics and Ads tags if you accept the consent prompt. Those measure page visits and store-link clicks. They never receive your audio, because nothing does. Full privacy policy.
Converted files are never stored by this page — they exist only in this tab until you download them.
Slowing it down to catch a word?
That is usually a transcription problem wearing a disguise. BlackBox turns recordings into searchable, time-stamped text on the phone itself — so you read the word instead of replaying it. Free on iPhone and Android.
Honest limits of this page
- ·Above about 2× music smears; speech holds up much better than anything else.
- ·Extreme slowdowns reveal the grains as a faint flutter. That is time-stretching, not a bug.
- ·Time-stretching a long file takes real seconds — it is doing arithmetic on every sample.
- ·The tape-speed mode changes pitch on purpose. It is not a fault when it does.
Read it instead
The free audio to text tool transcribes on your device, with clickable timestamps. Often faster than listening at any speed.
Cut the silence too
Speeding up a recording full of pauses just gets you faster pauses. The silence remover takes them out first.
How the audio speed changer works without uploading anything
Other sites make you send them your file, do the work on their computers, and send it back. Your browser can do the same work itself — and your file is already here. That is the whole trick.
Add the audio
Drop in a voice message, a lecture recording, an interview — anything your browser can play. It is decoded in this tab and goes no further.
Pick a speed
Tap a preset — 0.75× to follow a fast talker, 1.5× for the usual podcast skim — or drag the slider anywhere from a quarter speed to four times. The new length is shown before you press anything.
Decide about the pitch
Leave 'keep the voice sounding normal' on and only the clock changes. Turn it off and you get the tape-speed effect, pitch rising with the speed. The page tells you exactly how many semitones that is.
Save it as a real file
A player's speed setting lives in the player. This gives you a file that is genuinely at the new speed — one you can send to someone, or feed to a transcriber. MP3 or WAV.
Keeping the pitch is the hard part
Playing audio faster by reading it faster raises the pitch — the chipmunk effect, and the reason old tape tricks sound like a joke. Keeping the pitch means cutting the sound into overlapping grains and dropping or repeating them, sliding each one to where it lines up with what came before. That is WSOLA, it is the same family of algorithm ffmpeg's atempo filter uses, and it runs here in a background thread in your tab.
A file, not a player setting
Every podcast app has a speed button, but the file it sends on is still the original. Change the speed here and you get an actual file at the new speed: something you can forward, attach, or hand to a transcription tool. Slowing a mumbled voice message to 0.75× before transcribing it measurably helps.
Where it stops working
Speech survives 2× comfortably and 3× if the speaker is measured and alone. Music holds up worse — percussion smears first. Below about 0.5× you start hearing the grains as a faint flutter. The honest ceiling is 4×, and we will not pretend the result at that end is pleasant.
What people use it for
Slow a rushed voice message
Play it back at 0.75× with the voice still sounding like the person, and catch the word you kept missing.
Speed up a lecture you already understand
1.5× turns an hour into forty minutes, and the file stays a file — so it works in any player, on any device.
Slow speech down before transcribing
Clearer articulation at 0.8× measurably helps both human typists and automatic transcription on difficult audio.
Practise along with a recording
Musicians and language learners slow a passage down, learn it, then step the speed back up towards normal.
Slowing audio down to catch words is usually a transcription problem in disguise. The transcriber does it properly.
Audio speed changer — your questions, answered
How do I slow down audio without changing the pitch?+
Drop the file in, pick a speed below 1×, and leave 'keep the voice sounding normal' switched on. The audio is time-stretched rather than replayed slower, so the speaker's voice stays at its own pitch and only the pace changes.
Can I speed up a voice message and save it?+
Yes — that is the point of doing it here rather than in a player. Pick 1.5× or 2×, and you get a genuinely faster file back that you can forward, attach or transcribe. A player's speed button never changes the file itself.
What speeds can I use?+
Anything from 0.25× to 4×, with presets at the useful ones: 0.5× and 0.75× for catching words, 1.25× and 1.5× for skimming, 2× and 3× for getting through something. The finished length is shown before you start.
Does speeding up audio reduce the quality?+
Time-stretching is not free — grains are dropped or repeated, and at extremes you can hear it as a faint flutter or smearing. Speech survives it far better than music. Between 0.75× and 2×, most people cannot tell it was done.
How do I get the old chipmunk effect on purpose?+
Turn off 'keep the voice sounding normal'. The audio is then resampled instead of stretched, so pitch rises and falls with speed exactly like a tape machine. The page shows how many semitones the shift works out to.
Is anything uploaded when I change the speed?+
No. The file is decoded, stretched and re-encoded in your browser. There is no upload endpoint behind this page and no account to create, and it keeps working with the network switched off once the page has loaded.
Why does it take a few seconds on a long file?+
Because it is doing arithmetic on every sample, on your device, and correlating each grain against the last to find where it fits. That work is the difference between a natural-sounding result and a warbling one. Nothing is queued behind other people's jobs, which is the trade.
The rest of the audio toolkit
Also here: the audio converter, the compressor, the transcriber and the browser voice recorder. All free, all on your device.
Record your whole day, privately.
BlackBox is a 24/7 background voice recorder with scheduling, on-device transcription and local storage — about 14 MB an hour. Free on iPhone and Android.