How the Ear Hears Pitch

Understanding How the Ear Hears Pitch

The outer ear does more than collect sound. Its folds slightly change incoming waves, which helps the brain judge where a sound comes from. The eardrum then moves back and forth.

Three tiny middle-ear bones pass this movement into the inner ear. They act as a mechanical link between air and the fluid inside the cochlea.

Without this link, much of the sound energy would reflect away at the boundary. The final bone pushes on a small opening in the cochlea, creating pressure waves in its fluid.

Inside the cochlea is a long, curled membrane that responds differently at different positions. Near its base, the membrane is narrow and stiff, so it responds most strongly to rapid vibrations. Farther along, it is wider and more flexible, so slower vibrations travel farther before reaching their strongest point.

This creates a map of sound within the cochlea. Tiny hair cells sit along this map. When the membrane moves, hair-like bundles on these cells bend.

This opens channels in the cells and triggers messages in nearby nerves. The brain can use the location of active cells to estimate a sound's pitch. For slower sounds, it can use the timing pattern of nerve messages too.

Most real sounds contain many frequencies at once. A guitar string, a trumpet, and a human voice can produce the same musical note while sounding clearly different. Their difference comes from harmonics, which are extra frequencies above the main repeating pattern.

The balance of these harmonics gives each source its tone quality, or timbre. The brain is remarkably good at finding the main pattern even when it is weak or absent. This is why people can hear a clear note through a small phone speaker that cannot reproduce very low frequencies well.

When two instruments are nearly in tune, their waves create slow changes in loudness called beats. Musicians listen for these beats when tuning, because the beats become slower as the notes get closer together.

Pitch perception is not exactly the same for every person or every situation. A very loud sound can seem slightly different in pitch from a quieter version. Background noise can hide some frequencies and make speech harder to understand.

Damage from long exposure to loud sound often affects hair cells near the cochlear base first, making high notes harder to hear. Those cells do not grow back in humans. When learning this topic, separate pitch from loudness and timbre.

Pitch concerns the note heard. Loudness relates mainly to sound intensity.

Timbre helps identify the source. Listening to a piano, voice, or simple tone generator while watching a frequency display can make these differences easier to notice.