Audio Speed Changer
Load an audio file and play it back from 0.25× to 4× — slow down a tricky music passage or speed up a lecture — then export the result as a lossless WAV, all in your browser.
ℹ This is varispeed: like a tape or record player, speed and pitch change together (2× is one octave up, 0.5× one octave down). It is not pitch-preserving time-stretch — that needs a phase vocoder, which is out of scope here. Output is WAV (browsers can’t write MP3/AAC). Everything runs locally — your file is never uploaded.
How It Works
Your file is decoded to raw audio samples in the browser, then resampled to the speed you choose. At 2×, the tool reads the source twice as fast, so the result is half as long and plays an octave higher; at 0.5× it does the opposite. This is exactly how a tape deck or turntable changes speed — tempo and pitch move together. Rendering uses the browser’s high-quality resampler (an OfflineAudioContext), keeping the original sample rate and channel count, and the output is a lossless 16-bit WAV. Nothing is uploaded; everything happens on your device.
If you need to change tempo without changing pitch (or pitch without tempo), that’s time-stretching / pitch-shifting, which requires a phase-vocoder algorithm not included here. Use a desktop editor for that. For MP3 output, re-encode the exported WAV in a desktop app.