(Fr. tempérament égal; Ger. gleichschwebende Temperatur; It. temperamento equabile).
A tuning of the scale based on a cycle of 12 identical 5ths and with the octave divided into 12 equal semitones, and consequently with 3rds and 6ths tempered, uniformly, much more than 5ths and 4ths (see Temperaments, §1). Equal temperament is now widely regarded as the normal tuning of the Western, 12-note chromatic scale.
The term has been used in various contexts with slightly different meanings. Ellis used it for a theoretical scheme in which each semitone equals 100 cents, 1200 cents totalling an octave with a frequency ratio of 2:1. But piano tuners systematically depart from this model because their octaves are normally larger than 1200 cents (see Tuning, Table 1). A piano tuner makes the octaves sound ‘right’ melodically as well as harmonically – some tuners favour for melodic purposes more ‘stretch’ in the octave than others, particularly in the high treble and low bass – and makes the rate of beating of the 3rds and 6ths vary as smoothly as possible in the course of going up or down the scale chromatically. Achieving this smoothness, which many pianists take for granted as essential to the proper sound of the instrument, entails departing from the 100-cents-per-semitone model, especially in the tenor-baritone range where differences in string thickness and in timbre between overspun and plain strings must be compensated for. This and the need to camouflage an occasional faulty string accounts for many of the apparently whimsical departures from the 100-cent model (see illustration), which caused L.S. Lloyd in 1940 to publish an article wryly entitled ‘The Myth of Equal Temperament’. Organ Diapason pipes are much less problematical in this respect, and the use of an electronic tuning aid is correspondingly less likely to compromise the quality of the tuning.
Modern industrially produced woodwind instruments are designed to play in equal temperament, but performers can readily inflect the intonation to suit their musical tastes and ensemble requirements. Likewise, players of the lute, guitar or viol may depart considerably from the scheme of equal semitones embodied in the fretting of their instruments (see Temperaments, §9). For these performers, as for singers and violinists, the concept of equal temperament provides a simple intellectual model of the chromatic scale rather than a scheme of intonation that is strictly adhered to.
Scholars occasionally confuse equal temperament with late 17th- and 18th-century irregular tuning schemes that provide a circle of 12 good 5ths but, unlike equal temperament, contain a significant element of intonational nuance among various keys (see Well-tempered clavier).
Occasionally the term ‘equal temperament’ has been used loosely as a generic term for divisions of the octave into any number of equal parts.
For the history of equal temperament in performing practice and for bibliography see Temperaments, §§5, 8, 9 and bibliography (esp. Ellis, Barbour and White).
MARK LINDLEY