Diminished second
| Inverse | augmented seventh |
|---|---|
| Name | |
| Other names | - |
| Abbreviation | d2 |
| Size | |
| Semitones | 0 |
| Interval class | 0 |
| Just interval | 128:125 |
| Cents | |
| Equal temperament | 0 |
| 24 equal temperament | 50 |
| Just intonation | 41.1 |
In modern Western tonal music theory, a diminished second is the interval produced by narrowing a minor second by one chromatic semitone. It is enharmonically equivalent to a perfect unison. Thus, it is the interval between notes on two adjacent staff positions, or having adjacent note letters, altered in such a way that they have no pitch difference in twelve-tone equal temperament. An example is the interval from a B to the C♭ immediately above; another is the interval from a B♯ to the C immediately above.
In particular, it may be regarded as the "difference" between a diatonic and chromatic semitone. For instance, the interval from B to C is a diatonic semitone, the interval from B to B♯ is a chromatic semitone, and their difference, the interval from B♯ to C is a diminished second.
Being diminished, it is considered a dissonant interval.
In tuning systems other than twelve-tone equal temperament, the diminished second 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 (
play ), because both semitones have the same size. In 19-tone equal temperament, on the other hand, it is identical to the chromatic semitone and is a respectable 63.16 cents wide. It shows a similar size in third-comma meantone, where it coincides with the greater diesis (62.57 cents). The most commonly used meantone temperaments fall between these extremes, giving it an intermediate size.
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