How to use it
- Open a file.
- Choose a speed between 0.5× and 2×.
- Leave "Keep original pitch" on to time-stretch, or turn it off to change pitch with speed, like a record player.
- Apply and download.
Two kinds of speed change
With pitch kept, the audio is time-stretched: short overlapping windows are repeated or skipped so the length changes but the notes do not. With pitch unlocked, samples are simply played faster or slower, which shifts pitch by 12 × log2(speed) semitones: 2× is exactly one octave up.
Questions
Is my audio uploaded anywhere?
No. The file is decoded, processed and encoded by your own browser using the Web Audio API. Nothing is sent to a server, which is also why it works on large files without a queue.
What speed is best for studying a lecture?
Most people follow speech comfortably at 1.25× to 1.5×. Beyond 1.75×, consonants start to blur.