pitch

Sounds are perceived as high or low depending on their frequency, or the number of times per second a sound wave cycles from positive to negative and back to positive. The word that musicians most commonly use for frequency is pitch. The higher the frequency, the higher the pitch. Modifying the speed of a clip affects the pitch of the audio. Slow motion creates low pitch, and fast motion creates high pitch.

Helpful?

Final Cut Pro X User Guide

pitch