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
This audio speed changer decodes your file to raw audio samples in the browser, then resamples them 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. When you change playback speed this way — exactly like a tape deck or turntable — 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 audio to WAV conversion produces a lossless 16-bit output. Nothing is uploaded; everything happens on your device.
Popular use cases include slowing down audio for transcription and using it to slow down music so you can learn a difficult passage note-by-note: set the speed to 0.5× or 0.75× to make fast speech or a tricky melody easier to follow word-by-word. The pitch will drop (0.5× is one octave lower), but the words remain intelligible and the export gives you a permanent slow-motion copy to work from. Conversely, setting 1.5× or 2× is useful for speeding up a podcast or lecture when you want to absorb content faster — the classic “chipmunk” pitch rise is a side-effect of the varispeed method. To check the pitch of the original recording before or after processing, the Pitch Detector can identify fundamental frequency in real time.
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 such as Audacity or Adobe Audition for that. For MP3 output, re-encode the exported WAV in a desktop app. If you only need to cut out a section of the audio rather than change its speed, the Audio Trim Tool handles sample-accurate cropping without any re-encoding.