Tempo & Speed Changer
Slow down or speed up audio while holding the original pitch
100% In-Browser · Private & Instant · Free Forever
Your file is decoded, processed, and re-encoded in this browser tab. Nothing is uploaded to an OfflineTTS processing API.
Interactive Workspace
Tempo & Speed Changer
Change how fast a track plays without turning it into a chipmunk impression. Set the speed anywhere from 50% to 200% and the pitch stays where it was, because the tool time-stretches rather than resamples.
Why pitch is preserved: resampling is the cheap way to change speed, but it moves pitch at the same time. A phase vocoder separates the two: it analyses overlapping windows, tracks the phase advance between them, and re-synthesises at a new hop size. Speed changes, pitch does not.
Where this is genuinely useful:
- Slowing a fast passage down to learn it by ear
- Speeding a spoken take up to fit a fixed video duration
- Bringing a loop to a project tempo without repitching it
- Making a slow, deliberate version of an upbeat track
Where it struggles: dense percussion, heavily compressed masters, and material with long reverberant tails are the hardest cases for any phase vocoder. Slowing below about 70% makes those artefacts audible; speeding up is usually cleaner than slowing down.
Combine with other tools: to change speed *and* pitch together — the classic nightcore or slowed-and-reverb sound — use the dedicated Nightcore, Sped Up, Slowed + Reverb, or Vaporwave pages, which combine both stages in one render. Decoding, processing, and encoding all run in this browser tab. The file you select is not uploaded, and the rendered audio is not stored on any server.
How It Works
Load a track
Add the audio file whose tempo you want to change.
Set the percentage
100% is unchanged; 85% is slower, 125% is faster.
Render
The stretch runs offline in this tab — no upload, no queue.
Compare and export
Preview the result against the original, then download WAV or MP3.
Features
50% to 200%
Slow a track to half speed or push it to double.
Pitch Preserved
Phase-vocoder time stretch, so speed changes without repitching.
Instant Preview
Offline rendering produces a processed copy faster than real time.
Review Against Original
Switch the preview source to compare before and after.
Stretching Quality Depends on the Material
Time stretching is not a neutral operation. Every implementation makes a trade-off between preserving transients and preserving pitch, and different material exposes that trade-off differently. A solo piano recording stretched to 80% usually sounds convincing. A dense drum loop stretched to the same ratio usually develops a metallic ring around the transients.
If a stretch sounds wrong, the fix is usually to stretch less. Moving from 65% to 80% often makes the difference between an unusable and a perfectly serviceable result, and it is a much faster experiment than switching tools. For extreme slow-downs of percussive material, a DAW with a transient-aware algorithm will beat any browser implementation.
Speed, Pitch, and the Combination Tools
Speed and pitch are independent parameters, and the sound people describe as nightcore or slowed-and-reverb is a specific combination of both. This page changes speed only, which is the right choice when you need the material to stay in the same key — matching a video edit, fitting a voice-over to a slot, or practising a part.
Every effect here is deterministic: the same file and the same control values produce the same output. That means you can reproduce a result later, but it also means the tool will not guess what you intended — check a short excerpt before rendering a long file, and keep the original.
For the combined effects, use the dedicated pages. Nightcore raises speed to around 125% and lifts pitch to match; Sped Up raises speed with pitch held; Slowed + Reverb slows the track and adds a long reverb tail; Vaporwave slows further still and rolls off the top end. Each one is a fixed, reproducible recipe you can adjust afterwards.
Related Tools
Pitch Shifter
Transpose a recording up or down while keeping its original length
Nightcore Maker
Speed a track up with a matching pitch lift — the classic nightcore sound
Sped Up Song Maker
Raise the tempo and hold the pitch — fast but not squeaky
Slowed + Reverb Maker
Slow a track down and wash it in a long reverb tail
Tempo & Speed Changer — FAQ
Does changing the speed change the pitch?
No. This tool uses a phase-vocoder time stretch, which changes duration while preserving frequency content. If you want the sped-up nightcore sound where pitch rises with tempo, use the Nightcore or Sped Up tool instead.
How far can I slow a track down?
The slider goes to 50%, but artefacts become noticeable below roughly 70% on percussive material. Speech and sustained pads tolerate more stretching than drums.
Why does slowed audio sound smeared on drums?
A phase vocoder assumes roughly periodic content inside each analysis window. Sharp transients violate that assumption, so the algorithm spreads them across neighbouring windows. Every phase-vocoder implementation shares this limitation.
Can I use this to slow music down for practice?
Yes, that is one of the most useful applications. Slow a difficult passage to 70–80%, learn the part, then raise the speed back toward 100% as it becomes comfortable.
Does the result keep my original file?
Yes. The original on your device is never modified — the tool produces a new file when you download.
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