The mammalian ear converts sound waves into mechanical displacements that a row of receptor cells can detect.
Sound waves are vibrations of the air or of another medium.
They vary in both frequency and amplitude.
The frequency of a sound wave is the number of cycles (vibrations) that it goes through per second, designated hertz (Hz).
Pitch is a perception closely related to frequency.
We perceive a high-frequency sound wave as high pitched and a low frequency sound as low pitched.