how come when you speed up an audio track, the pitch also (usually) goes up?

Question

how come when you speed up an audio track, the pitch also (usually) goes up?

In: 38

Answer 1

Sound is vibration of air.
Pitch is defined by the number of vibrations per second.

When you speed up an audio recording, you are speeding up the vibrations that happen every second, and therefore the pitch goes up.

EDIT: if something is speeded up from normal speed and the pitch *doesn’t* go up in proportion (e.g. YouTube video speed), that is only possible because of audio processing to retain the original pitch.