Sound Perception: Pitch

By sound perception we mean the way we hear sound waves. The frequency range of sound audible to humans is approximately between 20 and 20,000 Hz. This range depends upon the individual and decreases with age. Sound with frequency below the lower limit of human hearing is called infrasound. Although we cannot hear infrasound, we may be able to feel it. Sound with frequency above the upper limit of human hearing is called ultrasound.

The musical notion of pitch is related to frequency. Usually the pitch of a sound is the fundamental or lowest frequency component - the higher the frequency the higher the pitch. However, when two pure sounds are played together we may perceive a pitch which is not actually a component of the sound present but has the frequency equal to the difference of the two frequencies.

Most people are able to distinguish between two sounds played separately which differ in frequency by as little as 2 Hz. When two sounds played simultaneously, most people are capable of detecting a difference in frequencies of 7 Hz. A sound which has no perceived pitch is called noise.

Two pitches in music are related not by their difference in frequency but by the interval between them which is defined by the ratio of their frequencies. The intervals and resulting scales for Western music are defined from the overtone series - see Music Intervals and Scales.

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