idea
The cochlea
The cochlea is a small coiled tube in the inner ear, about the size of a pea. Inside it runs a membrane that is narrow and stiff at one end and wider and looser at the other. High frequencies make the stiff end vibrate and low frequencies the loose end, so each place along the membrane responds to its own range of pitches. In this way the ear separates a sound into its frequencies before the signal reaches the brain, a little like a prism separates light into colours.