Changing speed and changing pitch are the same operation unless something actively works to separate them. Playing a recording back faster naturally raises its pitch, and playing it back slower naturally lowers it, because both effects come from the same underlying change: samples are being read at a different rate than they were recorded. Keeping the pitch steady while the tempo changes requires actually stretching or compressing the waveform in time, which is a real signal processing step, not a simple settings toggle.
Everything runs locally. The file is decoded by the Web Audio API, processed in your browser tab and encoded as WAV, so a private recording never has to be uploaded to change its speed.
What an audio speed changer is useful for
Podcasters commonly speed up interviews with long pauses, language learners slow down speech to catch every word, musicians slow down a solo to transcribe it note by note, and DJs and video editors both use an audio tempo changer to make two pieces of audio fit together. All of these are the same underlying request: play this file back faster or slower than it was recorded.
The two available modes matter for different reasons. Letting the pitch shift is closer to how physical tape and vinyl actually behave, so it suits anyone who wants that recognisable chipmunk or slow motion character. Keeping the pitch steady is the better choice whenever you need to understand the content clearly, such as transcribing lyrics or catching quiet dialogue, without the voice becoming a different register entirely.
- Use an audio speed changer to fit a voiceover into a fixed length video slot.
- Speed up long recordings such as interviews or lectures to save listening time.
- Slow down music or speech to transcribe or study it in detail.
- Choose pitch shifting for a deliberate creative effect, and pitch preservation for clarity.
Shifting pitch versus preserving pitch
The default, simplest way to change audio speed reads the decoded samples at a different rate through the Web Audio API's playbackRate property. This is efficient and introduces no artifacts of its own, but it inevitably raises the pitch when speeding up and lowers it when slowing down, since pitch and playback rate are tied together at this level.
The pitch preserving mode instead runs a time stretch algorithm over the raw samples before playback rate is touched at all. It works by breaking the audio into small overlapping windows, repositioning those windows further apart or closer together depending on the target speed, and blending them back together with a smooth crossfade between overlaps. The result changes duration without changing pitch, at the cost of some audible artifacts, particularly a faint warbling texture on sustained notes or vowels when the speed change is large.
Choosing a speed setting
Small changes, roughly between 0.85x and 1.3x, sound the most natural in either mode, since both pitch shifting and time stretching introduce fewer noticeable side effects the closer the target speed stays to normal playback. Podcast listening speeds in that range are common precisely because they save time without sounding obviously altered.
Larger changes toward 0.5x or 2x are still supported and can be useful for specific tasks like slow motion transcription or fast preview scrubbing, but expect the pitch preserving mode in particular to introduce more noticeable artifacts the further the setting moves from 1x.
How this audio speed changer processes the file
In pitch shifting mode, the decoded AudioBuffer is rendered through an OfflineAudioContext with its playbackRate property set to the chosen speed, which resamples the entire buffer in one pass and produces both the sped up or slowed down audio and its shifted pitch as a natural consequence of the same operation.
In pitch preserving mode, the overlap and blend time stretch described above runs first on the raw sample data for every channel, producing a buffer of the new duration at the original pitch. Both paths finish by encoding the result as a 16 bit PCM WAV file, since that is the format browsers can reliably write without a licensed codec.
How to change audio speed
- 1
Add your audio file
Drag an audio file onto the drop area, or click it to browse. MP3, OGG, FLAC, M4A, AAC and WAV are all accepted.
- 2
Set the speed
Move the speed slider between 0.5x and 2x. Values close to 1x sound the most natural.
- 3
Choose whether to preserve pitch
Turn on pitch preservation to keep the voice or instrument in its original register, or leave it off for a natural pitch shift.
- 4
Process and download
Press process, wait for the rendering to finish, then download the result as a WAV file.
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Sources and further reading
Frequently asked questions
Common questions about the audio speed changer.
Only when pitch preservation is turned off. With it off, speed and pitch change together the way a tape does when it speeds up or slows down. With it on, a time stretch algorithm keeps the pitch close to the original while still changing the duration, at the cost of some audible artifacts on sustained sounds.
Keeping pitch steady while changing tempo requires stretching or compressing the waveform in overlapping windows and blending them back together, and that blending is not perfect. The result is a faint warbling or phasing texture, most noticeable on sustained vowels or held notes, and most pronounced at large speed changes.
Keep the change moderate, roughly between 0.85x and 1.3x, and turn pitch preservation on. Both pitch shifting and time stretching introduce fewer artifacts the closer the setting stays to normal speed, so small adjustments in either mode stay easy to understand.
Yes. Slowing a recording to around 0.7x or 0.8x with pitch preservation turned on keeps the voice recognisable while giving you more time to catch each word, which is exactly the use case pitch preserving time stretching was built for in this tool.
The result downloads as a standard 16 bit PCM WAV file regardless of which mode you use. Browsers cannot reliably re encode a compressed format like MP3 without a licensed codec, so WAV is the honest output for processing performed entirely with web technology.
No. Decoding, the speed change itself and the final WAV encoding all happen locally using the Web Audio API. The file is never transmitted to a server, so a private recording stays private regardless of which speed or pitch setting you choose.