Frequency (Auditory)

Humans can detect sound waves with frequencies that vary from approximately 20 to 20,000 Hz. Probably of greatest interest to psychologists are the frequencies around 500–2,000 Hz. Sounds important to the act of speech typically occur in this range. Humans are most responsive to sounds between 1,000 and 5,000 Hz and are not likely to hear very low or very high frequencies unless the sound is quite intense. For example, the average person is approximately 100 times more sensitive to a sound at 3,000 Hz than to one at 100 Hz. People can best differentiate between two similar pitches when they are between 1,000 and 5,000 Hz.

When an individual hears a complex sound consisting of many different wavelengths, such as a human voice, music, or most sounds in nature, the ear separates the sound into its different frequencies. This separation begins in the inner ear, the basilar membrane within the cochlea. The basilar membrane is a strip of tissue that is wide at one end and narrow at the other. When the ear responds to a low frequency sound, the entire length of the basilar membrane vibrates; for a high frequency sound, the movement of the membrane is restricted to locations near the narrow end. Thus, a person can hear the different frequencies, and their associated pitches, as separate sounds.

The ability to hear declines with age, although the loss is greatest for high frequency sounds. At age 70, sensitivity to sounds at 1,000 Hz is intact, whereas sensitivity to sounds at 8,000 Hz is markedly diminished. As many as 75% of people over age 70 have experienced some deterioration in their hearing.

See also Hearing ; Just noticeable difference ; Sensation .