Audio speed changes — Verify the result

Worked example

The downloaded file should last the source length divided by the multiplier, so a 60-second clip at 0.8× should read about 1:15.

Allow a fraction of a second either way when you open the file and read its length.

The file name helps you keep versions apart. The tool saves it as the original name plus a suffix such as -slow-down or -speed-up with the extension of the format you chose, and the result card lists format, duration and size for a first sanity check.

Listen at three points: the first sentence, the middle, and the last 10 seconds. If the end of the recording sits earlier or later than the video or slide it should match, the length is off and you should recheck the multiplier you typed or dragged to.

A common mistake is judging only the first few seconds. Quality problems from tempo stretching show up on fast consonants such as s, t and k and on long vowels, so choose a passage with plenty of those and play it on headphones and on a phone speaker.

A numeric cross-check helps: at 192 kbps the 75-second result should weigh roughly 1.8 MB, at 128 kbps about 1.2 MB. A file far larger or smaller than that hints that a different format or bitrate was selected than the one you intended.

60 s at 0.8×

75 s theoretical duration

Compare against the original side by side; if the voice sounds robotic only at the fastest phrase, lower the multiplier slightly instead of re-exporting at a higher bitrate.