Audio tempo shift — change speed while keeping pitch
Stretch or compress audio files (MP3 / WAV / M4A / AAC / FLAC / OGG / Opus) by tempo (playback speed) without affecting pitch. Powered by soundtouchjs (SoundTouch library time-stretching) running on Web Audio API samples, from 0.5x (half speed) to 2.0x (double). Great for slowing down language-learning clips, transcribing tricky musical phrases, refining narration timing, or producing a 2x podcast cut. Export to WAV or MP3 with batch support. Your audio stays inside your browser — nothing is uploaded.
How to use
Drop or pick one or more audio files (MP3 / WAV / M4A / AAC / FLAC / OGG / Opus). Set the tempo with the slider (0.5x to 2.0x). 1.0x is the original speed. Pick the output format (WAV or MP3). For MP3, choose a bitrate. Click Shift tempo. soundtouchjs processes everything in the browser. Long clips take proportionally longer. Save files individually or grab the whole batch as a ZIP.
FAQ
- Does pitch stay the same?
- Yes. soundtouchjs decouples tempo and pitch, so playback speed changes while the pitch is preserved.
- What if I crank the slider all the way?
- You can go as far as 0.5x or 2.0x, but artifacts (warble, smearing) become obvious past about ±25%. Keep within 0.8x–1.25x for natural quality.
- WAV vs MP3?
- Pick WAV for DAW work or lossless preservation. Pick MP3 for sharing. MP3 is lossy; repeated re-encodes will progressively degrade quality.
- I want to change pitch too.
- This tool is tempo-only. Use the audio-pitch-shift tool for pitch. To change both at once (a simple fast/slow), you can also rewrite the WAV sample rate after export.
- Is anything uploaded?
- No. soundtouchjs and the Web Audio API run entirely inside your browser.
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