microtone

In music, any precisely determined division of the octave smaller than a semitone.

Examples of quarter-tone divisions are heard in the violin solo parts of Béla Bartók's Violin Concerto No 2 (1937–38), Alban Berg's Chamber Concerto (1923–25), and Pierre Boulez's cantata Le Visage nuptial/The Bridal Countenance (1946 rev. 1950–51). The Czech composer Alois Hába and Mexican Julián Carrillo composed in smaller divisions, and since 1984 Karlheinz Stockhausen has developed notations of up to 16ths of a tone for basset horn and flute, for example in Xi (1986) for basset horn.

Normally microtones belong in the domain of expressive pitch variation in acoustic music, being difficult to notate and perform precisely because most instruments other than the voice or violin family are designed to produce tempered pitches, or have fixed frets or keys. When played against a drone, however, they become more clearly quantifiable as audible beat frequencies. Conversely, electronic music is virtually unlimited in the extent and precision to which it can break down the octave.