Audio speed changer
Choose an audio file, pick a speed from half to double and save the result. It runs in your browser and nothing is uploaded.
Free · no signup Runs in your browser
How do I speed up or slow down an audio file?
Choose the file, move the speed slider (1× is normal, 2× is double speed, 0.5× is half speed) and press Save. The sound is re-rendered at the new speed in your browser and saved as MP3 or WAV. Changing the speed this way also changes the pitch, as when a tape or record plays faster, so voices at 2× sound higher.
How the speed is changed
There are two ways to change the speed of a recording. Time-stretching keeps the pitch the same and needs complicated processing. Resampling plays the samples faster or slower, which is simple and perfectly clean, but the pitch moves with the speed: at double speed everything is an octave higher, and at half speed an octave lower. This tool resamples, the same as playing a tape or a record at a different speed.
That suits many jobs: speeding up a lecture or an audiobook to get through it, slowing a piece of music to learn it, checking a recording at half speed to catch a word, or making a sound effect. If you need the pitch to stay natural for speech, keep the change small, since up to about 1.25× a voice still sounds normal. The new length is the old length divided by the speed, and the tool shows it as you move the slider.
It runs in your browser. Your file is never uploaded, and there is no watermark or sign-up. MP3 encoding uses LAME (lame.sourceforge.io), an open-source encoder, licensed under the LGPL.
How it works in detail
The sound is played at a new rate by the browser's audio engine (an OfflineAudioContext with a playbackRate) and written as WAV or MP3, so the new length is the old length divided by the speed. The speed can be set from 0.5× to 2×. The change is made by resampling, which keeps the quality of the sound but moves the pitch: each doubling of speed raises the pitch by one octave (12 semitones), so 2× is half the length and one octave higher, and 0.5× is twice the length and one octave lower. The result has the same sample rate as the original. To keep the pitch while changing the speed you need a time-stretch tool, which this is not.
How to use it
- Choose the audio file.
- Move the speed slider: 1× is normal, 2× is double speed and 0.5× is half speed.
- Choose MP3 (and a quality) or WAV (no loss).
- Press Save and wait while the sound is re-rendered.
- Download the result.
What changes and what stays the same
What the tool does to your file, and what it leaves alone.
| Aspect | What happens |
|---|---|
| Length | Old length ÷ speed |
| Pitch | Changes with the speed: up for faster, down for slower |
| Sample rate | Kept |
| MP3 quality | MP3 is lossy: each save as MP3 costs a little detail, so keep your original |
| Tags | Not copied |
| Privacy | Your file is read on your device and is not uploaded; there is no account and no watermark |
When to use it
- Listening to a lecture or an audiobook faster
- Slowing a recording to transcribe it or to learn a tune
- Making a sound effect from a recording
- Fitting a clip into a set length
Problems you may run into
Most problems come from the file itself, not from the tool.
| What you see | Likely cause | What to do |
|---|---|---|
| Voices sound high and squeaky | Speeding up raises the pitch | Use a smaller change, or a time-stretch tool that keeps the pitch |
| I need more than 2× | The range is 0.5× to 2× | Run the result through the tool again |
| The result is longer than expected | A slow speed makes it longer | Check the speed on the slider |
| Quality dropped | MP3 re-encodes the sound | Save as WAV |
| The file will not open | Your browser cannot decode this format, or the file is damaged | Try Chrome, Edge or Firefox on a computer, or open the file elsewhere to check that it plays |
| The browser slows down or stops | A very large file is processed on your own device | Close other tabs, try a computer, or use a smaller file |
Mistakes it helps you avoid
- Expecting the pitch to stay the same: it changes with the speed.
- Going very fast on speech: it becomes high and hard to follow.
- Saving to MP3 again and again: each save loses a little quality.
- Forgetting to keep the original.
How it works
Your audio is decoded, changed and saved inside your browser.
new length = old length ÷ speedspeed 2× = half the length and one octave higher; 0.5× = twice the length and one octave lowerthe samples are played at the new rate by the browser's audio engine (OfflineAudioContext, playbackRate) and written as WAV or MP3
Speed can be set from 0.5× to 2×. The change is made by resampling, which keeps the quality of the sound but moves the pitch: each doubling of speed raises the pitch by one octave (12 semitones). The result has the same sample rate as the original. To keep the pitch while changing the speed you need a time-stretch tool, which this is not.
Example: a 30-minute lecture at 1.5×
You speed up a 30-minute lecture to 1.5×.
- New length30 ÷ 1.5 = 20 minutes
- PitchRaised by about 7 semitones (log2(1.5) × 12 = 7.0)
A 20-minute file that sounds higher
For speech, 1.25× keeps a more natural sound.
Terms on this page
- Resampling
- Playing samples faster or slower, which changes both speed and pitch.
- Octave
- A doubling of pitch; 12 semitones.
Common questions
Does the pitch change?
Yes. Speeding up raises the pitch and slowing down lowers it, as with a tape. Each doubling of speed is one octave.
What speeds can I choose?
From 0.5× (half speed) to 2× (double speed).
Is my audio uploaded?
No. Your browser reads and changes the sound on your own device. Nothing is sent over the network.
Can I keep the pitch the same?
Not with this tool. That needs time-stretching, which is a different process.
What formats can I use?
Any your browser can play. The result is MP3 or WAV.
Where these numbers come from
- MDN Web Docs — OfflineAudioContext How a browser renders audio faster than real time, used to change speed.
- MDN Web Docs — AudioBufferSourceNode.playbackRate How playing audio faster or slower also changes its pitch.
- MDN Web Docs — BaseAudioContext.decodeAudioData() How a browser decodes an audio file into samples.
- LAME MP3 encoder (lame.sourceforge.io), LGPL The MP3 encoder, here a JavaScript port (lamejs) used unmodified as a separate file.
- MDN Web Docs — Using files from web applications How a page reads a file you choose without uploading it.
Last verified 2026-10-25 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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