Microtone

A microtone is an interval smaller than a half step, the smallest step on a piano. The best known is the quarter tone, half of a half step: 50 cents in a system where the half step measures 100. But a microtone can be any size below a half step, and music built on such intervals is called microtonal.

Where microtones are used

The piano's 12 equal steps are only one way to divide the octave. Many traditions use intervals that fall between the piano keys:

• Arabic maqam music uses intervals between a major and a minor second, often written with quarter-tone accidentals, although performers tune them by ear and tradition rather than to exact quarter tones.
• Turkish makam music is usually described with a finer division of the whole step into small units called commas.
• Indian classical music speaks of shrutis, traditionally 22 to the octave, from which the notes of each raga are drawn and inflected.
• Blues singers and players bend notes, especially the third and the seventh, into the space between minor and major (the blue notes of blues).

In Western concert music, 20th-century composers explored microtones systematically. Charles Ives wrote pieces for two pianos tuned a quarter tone apart, and Harry Partch built his own instruments for a scale of 43 notes to the octave.

Writing microtones

Standard notation has no microtonal signs, so composers add their own. The most common are quarter-tone accidentals: a sharp with one vertical stroke (a quarter tone up), a sharp with three strokes (three quarter tones up), a reversed flat (a quarter tone down), and ordinary accidentals with arrows attached.

Playing microtones

Instruments with continuous pitch can play microtones directly: the voice, the violin family, the trombone and fretless instruments. Guitarists reach them by bending strings, and wind players use special fingerings and lip adjustments. A normally tuned piano cannot, but many synthesizers and MIDI instruments can retune every key.

Even in ordinary playing, musicians use tiny pitch changes constantly. Vibrato moves around a pitch by less than a half step, and good intonation means adjusting by a few cents to blend with others.

Hear a guitar bend travel toward its target pitch in Bend Toward a Note, and see how a pitch can move without changing its name in One Note, Moving Pitch.