In tuning systems other than 12-tone equal temperament and its multiples, the diminished second is a distinct interval. It can be viewed as a
comma, the minute interval between two
enharmonically equivalent notes tuned in a slightly different way. This makes it a highly variable quantity between tuning systems. Hence for example C is narrower (or sometimes wider) than D by a diminished second interval, however large or small that may happen to be (see image below). In 12-tone
equal temperament, the diminished second is identical to the
unison (), because the chromatic and diatonic semitones have the same size. In
19-tone equal temperament, which extends -comma
meantone, it is identical to the chromatic semitone and is a respectable 63.16
cents wide. The most commonly used
meantone temperaments fall between these extremes, giving it an intermediate size. However, in
53-tone equal temperament, which extends
Pythagorean tuning, the interval actually shows a descending direction, i.e. a ratio below
unison, and thus a negative size, going one step down. In general, this applies for all tunings with fifths wider than 700 cents. The table below summarizes the definitions of the diminished second in the main tuning systems. In the column labeled "Difference between
semitones",
m2 is the minor second (diatonic semitone),
A1 is the augmented unison (chromatic semitone), and
S,
S,
S,
S are semitones as defined in five-limit tuning#Size of intervals. Notice that for 5-limit tuning, -, -, -, and -comma meantone, the diminished second coincides with the corresponding commas. ==See also==