OneTaskBy Tim King · Updated
Audio Speed Changer
Keep the Pitch or Shift It Like Tape, Half to Triple Speed
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How the Audio Speed Changer works
This audio speed changer runs entirely in your browser. Drop a file in, drag the slider to the speed you want, and choose whether the pitch should stay put. Drag on the waveform to change only part of the file. The stats show the new length before you export. Preview plays the result, and export writes it as WAV or MP3. Nothing is uploaded.
How the audio speed changer works
There are two quite different ways to make audio faster or slower, and the Keep pitch setting chooses between them.
Keep pitch: Yes. The audio is time-stretched: the file gets shorter or longer but every note and every voice stays at its original pitch. This is what you want for speeding up a lecture, slowing down a fast passage to learn it, or fitting a voice-over to a video cut. The page does it with a waveform-similarity overlap-add method, which slices the audio into small overlapping grains and re-spaces them, lining each grain up with the previous one so the joins fall on matching waveform cycles. Speech survives this very well up to about double speed and down to about 70 percent; beyond that, a slight granular texture becomes audible, especially on sustained musical notes.
Keep pitch: No. The audio is resampled, exactly as if a tape were run faster or slower. Speed and pitch change together, so 200 percent is an octave up and 50 percent an octave down. This is perfect for sound design, for the classic sped-up-voice effect, and for any case where the pitch shift is part of the point. It is also lossless in the sense that no grains are involved: every output sample is an interpolation of the input.
Changing only a section. Drag across the waveform to select a region and only that region is sped up or slowed down. The parts before and after are unchanged and the whole file is exported together, which is useful for tightening one slow answer in an interview without altering the rest.
Practical ranges. Podcast listeners commonly use 120 to 150 percent, and speech is still perfectly intelligible at 200 with the pitch kept. Slowing to 50 percent with pitch kept is the classic "learn this solo" setting; the artefacts are audible but the notes are clear. For a tape-style slowdown, 50 percent is an octave down and can make a snare sound like thunder.
Output. The exported file has the same channel count and sample rate as the source. WAV is the safe choice if you plan to process it further.
FAQ
Which mode should I use for a podcast?
Keep pitch Yes. It makes the speaker faster without turning them into a cartoon. Somewhere between 125 and 175 percent suits most listeners, and the words stay perfectly clear.
Why does the stretched version sound slightly grainy?
Time-stretching without pitch change has to cut the audio into grains and re-space them, and at extreme ratios the joins become audible as a faint flutter. Keep the change under about double or half speed for clean results, or use the pitch-shifting mode where no grains are involved.
Can I change speed and pitch independently?
Not on this page, which offers pitch-locked or pitch-following. The Audio Pitch and Speed tool has separate controls for each if you need a specific combination.
How long does processing take?
Resampling is near-instant. Time-stretching walks through the whole file comparing waveforms, so an hour of audio takes a few seconds on a modern laptop; the progress bar shows where it is.
See also: all Audio tools, Images, Video & Screen, PDF, SVG, Simulations & Screensavers, Generative Art, Chart Makers, 3D Model Viewers, Drawing Pads, Mockups & 3D Making, Diagram Makers, 3D Science, Tracker Music.
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