Audio speed changes — Settings and quality

Worked example

Choose the speed by purpose: 0.75× to 0.85× for dictation, 1.25× to 1.5× for catching up on lectures, and 2× or more only for skimming.

The slider runs from 0.25× to 4× in steps of 0.05, with preset buttons at 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 3 and 4.

Extreme values cost quality. Past 2× or below 0.5× the tool chains several tempo stages, and consonants start to sound watery or choppy, so when the speech must stay intelligible a single 1.5× is safer than a single 3×.

Export settings decide size and a second round of loss. A 75-second result at 192 kbps MP3 is about 1.8 MB, 128 kbps is plenty for plain speech at about 1.2 MB, and WAV avoids another lossy encode but weighs roughly 10.6 MB per minute at 44.1 kHz stereo.

Slowing down grows the file because the same bitrate now covers more seconds: 0.8× adds a quarter to the length and so to the size. Choosing Mono in the Channels menu halves the data again for voice recordings that were never stereo.

A practical recipe for a beginner dictation: 0.8×, M4A or MP3 at 128 kbps, sample rate kept from the source. Run it once, listen to the fastest sentence, and only then try 0.75× if learners still struggle. Write the chosen value in the file name so the choice is easy to repeat.

60 s at 0.8×

75 s theoretical duration

Pick one multiplier per output file and keep the original; stacking a slow-down and a speed-up does not restore the source.