Different pitches refer to the perception of sound varying in frequency. It is the quality that distinguishes a high-pitched sound from a low-pitched one.
The basilar membrane is a structure located in the cochlea of the inner ear. It vibrates in response to different frequencies of sound waves and helps us distinguish between various pitches.
According to place theory, different areas along the basilar membrane respond to specific frequencies of sound waves. This theory explains how we perceive different pitches based on where these vibrations occur within the cochlea.