Terminology
Microtonal music can refer to all music which contains intervals smaller than the conventional contemporary Western semitone. The term implies music containing very small intervals but can include any tuning that differs from the western 12-tone equal temperament. Traditional Indian systems of 22 śruti; Indonesian gamelan music; Thai, Burmese, and African musics, and music using just intonation, meantone temperament, or other alternative tunings may be considered microtonal.
(Griffiths and Lindley 1980; Griffiths, Lindley, and Zannos 2001). Microtonal variation of intervals is standard practice in the African-American musical forms of spirituals, blues and jazz (Cook and Pople 2004, 124–26).
Many microtonal equal divisions of the octave have been proposed, usually (but not always) in order to achieve approximation to the intervals of just intonation. (Griffiths and Lindley 1980; Griffiths, Lindley, and Zannos 2001)
Terminology other than "microtonal" is used by theorists and composers. Ivan Wyschnegradsky used the term ultra-chromatic for intervals smaller than the semitone and infra-chromatic for intervals larger than the semitone (Wyschnegradsky 1972, 84–87). Ivor Darreg proposed the term xenharmonic. (See xenharmonic music).
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