In general, a musical interval smaller than a semitone. Much non-Western music, such as Indonesian gamelan and Indian classical music, and some twentieth-century art music is composed using microtonal scales.
Pythagoras defined a pleasant sounding series of pitches with even-integer ratios (see WFTD Just Intonation) using a vibrating string a few thousand years ago, essentially setting the standards for virtually all western music. In actual practice, however, tuning standards are often more of a general agreement than a mathematical reality (see WFTD Equal Temperament). A practically unlimited number of intervals are possible, each with its own set of overtones and interactions with the others.
Some western composers have employed microtonal scales, dividing an octave into 19, 24, 31, 43, 72 and other numbers of pitches, rather than the more common 12. Many synthesizers offer alternate tuning options that include not only just intonation and equal temperament, but also quarter tone, Indian, Javanese, Balinese, and other scales.
