Human hearing spans 20 Hz to 20 kHz and splits 1,500 pitches

Healthy human ears respond to sound from about 20 hertz to 20,000 hertz (20 kHz), and within that band they can tell apart roughly 1,500 separate pitches, fine enough to hear the difference between a 440 Hz and a 441 Hz tone.

How does the ear sort pitches?

In the cochlea, a fluid-filled, snail-shaped coil in the inner ear lined with some 16,000 to 20,000 sensory hair cells. Sound sets a travelling wave rippling along the basilar membrane inside it, and the hair cells riding that wave turn its motion into electrical signals for the brain.

The coil is laid out by pitch. Hair cells near its wide end respond to high-pitched sounds, such as an infant crying; those toward the centre pick up low-pitched ones, such as a large dog barking. The ear is also startlingly sensitive: it can detect pressure changes of less than one billionth of atmospheric pressure, and at the threshold of hearing the air vibrates by about a tenth of an atomic diameter. Fitting 1,500 distinct pitches along the coiled membrane would need a separately tuned spot every 0.002 cm, too fine for a simple vibrating membrane, so some extra pitch-sharpening mechanism must be at work.

Can everyone hear from 20 Hz to 20 kHz?

No. The 20 Hz to 20 kHz window is the textbook range for healthy ears, not a guarantee. Unlike the hair cells of birds and amphibians, human hair cells don’t grow back, so damage from noise and age accumulates over a lifetime.

The toll shows up clearly in later life. About one in three people in the U.S. aged 65 to 74 has hearing loss, and nearly half of those older than 75 have difficulty hearing.