EQUAL TEMPERAMENT

also called Well-tempered Tuning, in music, tuning system in which the octave is divided into 12 semitones of equal size. Because it enables keyboard instruments to play in all keys, the system replaced earlier tuning systems in France and Germany by the late 18th century and in England by the 19th; before its use on keyboard instruments, it was used for fretted instruments, such as the lute. Although Andreas Werckmeister, a German organist and theorist, is usually credited with devising the system in about 1700, he was preceded by the physicist Marin Mersenne in 1685 and, outside Europe, by the Chinese prince Chu Tsai-y in 1596. The Florentine music theorist Vincenzo Galilei (father of the astronomer Galileo) proposed a very similar system in 1581. In addition, equal temperament was approximated in various degrees in the minor tuning adjustments made by organ tuners and harpsichordists. Johann Sebastian Bach's The Well-Tempered Clavier (1722, 1744) may well have been written for such a practical tuner's system. In equal temperament, each semitone is measured at 100 cents (1 cent = 1/1200 octave). Because tuning is calculated by dividing up the octave into smaller units, equal temperament is a divisive system; earlier European systems were cyclici.e., they calculated new intervals by adding together previously determined intervals. In equal temperament, a fifth, such as CG, is imperceptibly narrower than the fifth found in the natural harmonic series (see overtone) by 2 cents; but it is not as much smaller than the fifth used in the previous tuning system, meantone temperament. The interval of a third in meantone tuning is pure, or natural; in equal temperament, it is noticeably wider (14 cents). Compare meantone temperament.