Audition: Pitch Perception

Sound

Sound has the physical dimensions of frequency, level, and time. Sound is caused by objects that vibrate and send out sound waves. Frequency refers to the rate at which an object vibrates, and level refers to the magnitude of that vibration. Hertz (Hz) is the physical measure of frequency. A sound with a 100-Hz frequency is a sound whose vibratory pattern repeats 100 times per second; if the vibration occurs at rate of 1,000 times per second, the sound's frequency is 1,000 Hz, and so on. The perception of pitch is the auditory system's means of processing information about the physical properties of sound: frequency, level, and time. When the physical frequency of the sound from a source varies, it is almost always perceived as a pitch change. A short string on a violin vibrates faster than a longer string does and produces a high-frequency sound that is perceived as a high pitch. But many other aspects of frequency, level, and time can lead to the perception of pitch. The study of pitch perception involves understanding the relationship between the physical properties of sound and the subjective perception of pitch. As of yet, there is not a complete understanding of these relationships and, as a consequence, the study of pitch perception is an active area of research in the auditory sciences.

Measuring Pitch

The standard definition of pitch is that pitch is that subjective attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from low to high. Pitch is measured subjectively in three ways: using musical scales, using a frequency scale, and occasionally using the mel scale. The musical scale contains notes (in Western music, 12 notes: A, B, C, D, E, F, G, and in the sharps, #, and flats, b: Ab, Bb, F#, A#, Eb). The musical scale may be divided into octaves. An octave is a doubling of frequency (880 Hz is the octave above 440 Hz, and 220 Hz is the octave below 440 Hz; 440 Hz is the approximate vibratory frequency of the musical note A played in the middle octave of the piano keyboard). Each octave can be divided into 12 equal logarithmic divisions called semitones. Thus, all the A notes on a piano keyboard are separated from each other by an octave, and each of the 12 notes (e.g., black and white keys on the piano keyboard) within an octave are spaced in frequency by about a semitone. Each semitone has 100 cents (hence an octave has 1,200 cents). Musical notes, semitones, and cents are used as scales to measure pitch.

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