I know that D♭ - E♭ is a major second. What is the interval D♭ - D♯ called (and why)?

  • He wrote "diminished third", not minor. What is wrong is the "/". Those are different kind of intervals. If you leave out any other parameter, like volume and 'timbre', on a piano or similar tuned instrument the resulting sound is indeed the same. But this is never the case. Even on a piano, with its equal tuning, interpreters and analyst react different to an Eb than to a D#. These two notes have two different functions and the interpreter knows the difference and plays them different, with whatever possibilities his/her instrument has.
    – nilshi
    Aug 8, 2012 at 18:02
  • 1. why is a diminished 3rd equal to an "absolute interval" of 2 halfsteps? Isn't a "regular 3rd" a major 3rd? And diminishing it makes it equivalent to a minor 3rd doesn't it?? 2. On an equal tempered piano, I can see Eb and and D# from different key signatures sounding "different" due to the key signature's tonic. But they ARE the exact same sound, aren't they? Aug 8, 2012 at 20:20
  • 1
    If you get a diminshed 3rd wrong and only count half steps you end up with the sound of a major second. @Stephen Hazel: That is what I meant with the "/" in the question is wrong because major second is not diminished third, even-though under special circumstances they sound the same. Also, to correct your comment, A dimished third is not the same as the minor one. It is one step further. C-E is major C-Eb is minor C-Ebb is diminished and may sound like C-D. Leave the tuning aside, this is only remotely connected to tuning. It is orthography.
    – nilshi
    Aug 9, 2012 at 18:09

2 Answers 2


D-D is unison (or "prime")

Db-D or D-D# is augmented prime and Db-D# is a double augmented unison or prime.

P.S. This is really something different than the enharmonic variants Db-Eb, but that was not the question.

  • 3
    Double-augmented unison is correct.
    – mjibson
    Aug 8, 2012 at 18:56
  • 1
    Correct, and unison/prime are interchangeable.
    – NReilingh
    Aug 9, 2012 at 1:42
  • Why wouldn't you just call it a whole step or 2nd?
    – ChipJust
    Aug 17, 2012 at 21:16
  • 1
    @ChipJust It's enharmonic to a major one, but a 2nd would be some kind of D to some kind of E.
    – NReilingh
    Aug 18, 2012 at 12:57

Consider also the questioning of naming the unison an interval by italian music theorist Zarlino which I personally find very relevant (rather think of it as a point in geometry).

Equality is never found in consonances or intervals, and the unison is to the musician what the point is to the geometer. A point is the beginning of a line, although, it is not itself a line. But a line is not composed of points, since a point has no length, width, or depth that can be extended, or joined to another point. So a unison is only the beginning of consonance or interval; it is neither consonance nor interval, for like the point it is incapable of extension.

Source: http://en.wikipedia.org/wiki/Unison

  • So what do you call it then? If it's harmonically a D at both ends, it has to be some kind of unison or you're not accurately describing it. Admittedly, finding a valid case where you actually need to think about an interval that goes from Db to D# is pretty unlikely! Apr 30, 2015 at 14:47
  • 1
    This argument is completely flawed. An interval is a distance so saying a unison isn't an interval is saying zero isn't a distance which is just wrong.
    – Dom
    Nov 20, 2016 at 5:05

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