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I know that Db - Eb is a major second/diminished third. What is the interval Db - D# called (and why)?

EDIT: oops, Db - Eb is NOT a diminished third.

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My understanding is that Db->Eb is a major second, not a minor third. – Dave Aug 8 '12 at 17:44
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. – nilsge Aug 8 '12 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? – Stephen Hazel Aug 8 '12 at 20:20
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. – nilsge Aug 9 '12 at 18:09
ok, thank you - i think i follow it now :) – Stephen Hazel Aug 9 '12 at 19:23

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.

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I'd +1 this one, but I'm not 100% sure. – Dave Aug 8 '12 at 17:34
Double-augmented unison is correct. – mjibson Aug 8 '12 at 18:56
Correct, and unison/prime are interchangeable. – NReilingh Aug 9 '12 at 1:42
Why wouldn't you just call it a whole step or 2nd? – ChipJust Aug 17 '12 at 21:16
@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 '12 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.


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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! – Matthew Walton Apr 30 '15 at 14:47

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