I was just calculating some intervals and then came across something special: if I have the notes B-Fb, what is the interval between them called? Since B-F# is a fifth, B-F must be a diminished fifth, and that would logically lead me to believe that B-Fb is a double diminished fifth, but is that a valid word?

I realize that Fb is enharmonic to E, because otherwise it would've been a perfect fourth, or so I think.

Thanks
Double-flat is the closest term I know of. Will that interval even be distinguishable from a perfect 4th?
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Yes, it would be a double diminished fifth. However, like you said, it would be enharmonic to a perfect fourth. It would depend on the context I suppose. If you had a scale that had a double diminished fifth in it, it would probably work. I don't see that being harmonically stable though (Or even harmonic at all).
Back in my day you didn't double a diminished interval and real men didn't play a scale more exotic than the fruit he could find at the local market.
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I can't think of a way to use any double diminished interval.

Although, you are correct that a perfect interval flattened becomes diminished and flattened again becomes double diminished. Major intervals flattened become minor and double flattened become diminished. I guess if you triple flatten a major interval it becomes double diminished.... but now we are getting silly aren't we?

I am sure a composer (maybe Corwin?) would know exactly where and how these intervals are used.

oh how he must laugh..........
You'll only find that in situations where you have to bypass logic straight into reason, i.e. atonality, especially serialism. Since that's not what you're doing, don't analyse it. So not overthink.
Cerasti, you are absolutely correct in calling that interval a "double diminished fifth" (coming from a theory and composition major, just to give that statement a little weight). There are also double diminished fourths, double augmented fifths, etc.

Often times, these intervals will be seen in music not because of a lowering of the upper note, but because of a raising of the lower note. For example, if you have a C to Gb interval in a piece, and while that Gb is holding out, the lower interval raises to a C#, whether in a chromatic movement or to achieve some sort of harmonic sound. Voila, double diminished fifth.
Last edited by PSM at Sep 16, 2008,
Yes it is a double diminished fifth...

You can have any interval you want really, from triple augmented unison to quintuple diminished sixth, etc...
But there is some consensus which decides which intervals are "useful" in western music, etc..
But if you go up in the circle of fifths, you can get any interval you want...
Quote by gonzaw
But there is some consensus which decides which intervals are "useful" in western music, etc..

You are looking at things backwards. Keep in mind that theory comes AFTER the music, and not before. It is used to describe what is going on in a piece, what might have been going on in the composers head, and possibly how a piece might be perceived by the listener's ear. It is (in most cases) not used to define the rules of a piece of music before that piece is written, or at least was not when that music originally came about.

Therefore, to say that certain intervals are "useful" or not is just plain wrong. The use of interval names such as "double diminished fifth" are often necessary because you have to take into account the music that comes before and after that specific interval. A C# / Gb interval, when written like that, will most often not be perceived by the listener as a Perfect Fourth when taking into account what led up to that interval and what comes after that interval.

Also keep in mind that in theory, the numeric portion of an interval is always labeled using the distance between each letter name. For example, a C to G = a fifth, regardless of what sharps or flats you put on those letters. An A to C is always a third, regardless of what sharps or flats you put on those letters. Therefore, if you come across a C# and Gb interval, it will be described as a double diminished fifth by theorists.
Quote by PSM
You are looking at things backwards. Keep in mind that theory comes AFTER the music, and not before. It is used to describe what is going on in a piece, what might have been going on in the composers head, and possibly how a piece might be perceived by the listener's ear. It is (in most cases) not used to define the rules of a piece of music before that piece is written, or at least was not when that music originally came about.

Therefore, to say that certain intervals are "useful" or not is just plain wrong. The use of interval names such as "double diminished fifth" are often necessary because you have to take into account the music that comes before and after that specific interval. A C# / Gb interval, when written like that, will most often not be perceived by the listener as a Perfect Fourth when taking into account what led up to that interval and what comes after that interval.

Also keep in mind that in theory, the numeric portion of an interval is always labeled using the distance between each letter name. For example, a C to G = a fifth, regardless of what sharps or flats you put on those letters. An A to C is always a third, regardless of what sharps or flats you put on those letters. Therefore, if you come across a C# and Gb interval, it will be described as a double diminished fifth by theorists.

That's what I said...
Double diminished fifths serve a function in music theory, that's why consensus (all those nerd greeks and classic guys) keeps it in mind..

But you will never see a 10th augmented second in any score, why? Because it serves no harmonic function in our western system, but it does exist and can be used...

Music theory explains music, it is independant of any individual piece of music, just in general.
If you apply an interval, it just means that between note A and note X there is xxxx cents/hertz of difference. THAT is explaining music, or sound or aural perception, and you don't have to write a single piece...
But, saying some intervals are useful or not depends on the system you are working in, which in turn depends on the culture you are in, which in turn depends on how said culture perceives music and how it allows/bans it, etc...

Of course I am talking about western system here, which already includes the whole "after music" stuff...
Quote by Cerasti
I was just calculating some intervals and then came across something special: if I have the notes B-Fb, what is the interval between them called? Since B-F# is a fifth, B-F must be a diminished fifth, and that would logically lead me to believe that B-Fb is a double diminished fifth, but is that a valid word?

I realize that Fb is enharmonic to E, because otherwise it would've been a perfect fourth, or so I think.

Thanks

Just to simplify the walls of text in this thread, the answer is yes. B-Fb would be a doubly diminished fifth. Regardless of what it's enharmonic to, if you see any sort of B to any sort of F, you'll know it's a fifth and you can work from there.
Well I read it all anyway, and I've gotten a satisfactory answer.

Thanks, everyone