Ok. So, the C13b5b9. What is it good for? Let's take a moment, shall we?
I'm specifically referring, at least for the moment, to the voicing for the guitar, beginning with an F#/Gb on the low E string, a C#/Db on the A, a muted D string, a Bb on the G, an E on the B, and an A on the E. If I tabbed it out, it could look like this:
And that, my friends, is a sad little tab.
OK, so let's look at it. First, of course, you will note that the b5 and b9 are in the bass. This makes for a peculiar sound. If you were to look at the notes, F#/Gb, C#Db
, Bb, E, and A, (I'm not going to double notate the sharp/flat thing any more. You can imagine that they are what you need them to be) you might note that they also spell out an F#7#9
(that's an F#, 7#9
, not an F #7#9
). That's among the peculiarities of this fun chord. Depending on context, it can function as either a C13b5b9 or an F#7#9
. Now, perhaps you also suddenly had an aha! moment and realized that these two are a tritone apart, and that with a tritone substitution, they have very similar functions. See? It's getting more interesting all the time.
Now, suppose you decide you don't like this chord and voicing, which I guess is more accurately called a C13b5b9/Gb, as well as I seem to. So, you decide to run the thing up the fretboard until there's a proper, self-respecting C in the bass. That seems pretty understandable, right? Then, you'd get this:
-8- (the same chord shape, 6 frets higher)
So, see, by running the chord up the fretboard until you get a nice, comfortable C in the bass, you've moved it up six frets, which is our friend the tritone. What does this mean? It means that by running it up to there, you have the same shape, higher, and it's still also an F#7
type chord, only now the two chords have switched. This is now a C7#9
and an F#13b5b9
. Neat, right, but what, besides just jumping from one to the other and saying "neat, right?" is it good for?
Well, it has a couple of uses.
The same way you can use an F# dimished7 in place of a boring old C7, with our good pal the tritone substitution (and trust me, you can), you can slap in a C13b5B9, which gives the interesting tonality of a straight substitution, and the potential for a chromatic walkup (from F/tonic) in the bass. The same goes for the C# diminished and the F#, only a tritone higher, or not, depending.
Yeah, see, that's the beauty of it. You can use either placement of the voicing, low or high, and it's still existing in this fragile middle ground place, between being a full-on 7th and some kind of peculiar diminished. It's still being both an F# diminished and a C7 and a C diminished an F#7
. This isn't actually because of any magic with this chord, it's our old friend again, the tritone. This just happens to be an interesting voicing of this chord.
OK, but what's it good for?
Sounding cool. That's always job one. What else? Well, if you want to look a little closer, it can stand in as a dominant chord, anywhere your progression (in the key of F, in this case) asks for a V7, but your sensibilities want something that isn't boring. It can be a slightly off-kilter ii, which can create fun peculiarities if you were to, say, use the lower voicing (the first one) as the ii, and then run it up to the higher (second) voicing as the V7. I dunno. I always think it's neat to use the same chord for two functions in a harmonic line, but then, I'm kind of a nerd. So, if you were going to do that, you'd maybe play the first chord above, then the second, and then either a plain old F, or some kind of Super Awesome F7 device. Or, if you wanted a really pretty thing, maybe an F6/9, which I will tab out below so you can resolve this fun semi-dischordant play-around, if you must.
Enjoy! Or, more likely, don't!