The pitch of a sound corresponds to the frequency of the wave. The higher the frequency, the higher the pitch.
A normal person can hear sounds with frequencies in the range 20 Hz to 20,000 Hz, but most sounds do not consist of a single frequency – they are made up of a range of different frequencies. The particular mix of frequencies determines the sound, with different mixes producing different sounds. Sounds of different frequencies are separated in the cochlea.
The cochlea is a spiral containing three chambers. The pressure wave starts from an oval window in the auditory (stirrup) bone attached to the cochlea and passes to the top of the spiral along the vestibular canal, returning via the lymphatic canal to the round window. Sensors (actually small hair like structures) in the organ of corti in the middle chamber – the cochlea duct – convert variations in pressure into electrical signals in the auditory nerve. Different size sensors respond to different frequencies or pitch, allowing sounds to be decomposed into frequencies and differentiated. This allows especially different voices to be distinguished.