Comma (music)

Comma (music)

In music theory, a comma is a minute interval, the difference resulting from tuning one note two different ways. The word "comma" used without qualification refers to the syntonic comma, which can be defined, for instance, as the difference between an F♯ tuned using the D-based Pythagorean tuning system, and another F♯ tuned using the D-based quarter-comma meantone system. Even within the same tuning system, when scales with more than 12 notes are built, two notes which should coincide may have a different tuning. For example, in extended scales produced with 5-limit tuning an A♭ tuned as a major third below C5 and a G♯ tuned as two major thirds above C4 will not be exactly the same note, as they would be in equal temperament. The difference between those notes, the diesis, also known as lesser diesis, is more than 40% of a semitone, and is easily audible.

Commas are often defined as the difference in size between two semitones, even within a single non-extended 12-tone scale. Each meantone temperament tuning system produces a 12-tone scale characterized by two different kinds of semitones (diatonic and chromatic), and hence by a comma of unique size. The same is true for Pythagorean tuning.

In just intonation, more than two kinds of semitones may be produced. Thus, a single tuning system may be characterized by several different commas. For instance, a commonly used version of 5-limit tuning produces a 12-tone scale with four kinds of semitones and four commas.

The size of commas is commonly expressed and compared in terms of cents – 1/1200 fractions of an octave on a logarithmic scale.