Quote:
|
Originally Posted by oxo_cubes
could someone (maybe that pretentious guy near the start of the thread since he knows so much and is so helpful) explain tritone substitution and how it is used?
that would be great, thanks
|
Tritone substitution is usually used when reharmonizing a song or part of a song.
As you know, a dominant 7th chord is made up of the root (1), a major 3rd (3), a fifth (5), and a minor 7th (b7). The third and seventh are what makes this chord. Even if you leave out the root and fifth, it still sounds like a dominant chord, incomplete though the chord may be.
As you may have noticed, the 3 and b7 are a tritone apart. You should also note that the 3 and b7 of a dominant chord are the
same notes as another dominant chord, specifically, the dominant chord a tritone away.
For instance, the G7 chord tones are G(1), B(3), D(5), and F(b7). A tritone away is Db7, which contains Db(1), F(3), Ab(5), and B(b7). Notice that the B and F are the 3rd and 7th of both chords, although inverted.
Because the two most important notes, the 3rd and 7th, are the same in both chords, the two chords can be substituted for one another.
If you didn't feel like reading all that, here is the basics of tritone substitution. Any dominant chord can be substituted for another dominant chord a tritone apart from the original chord.
Now, technically tritone subsitution can be used on any dominant chord. But of course, it does not always sound good. It sounds best if you a)
create a chromatic bass line, or b)
make the melody more interesting.
Tritone subsitution is often used in II-V-I's because it lends itself prefectly to creating a chromatic bass line. For example, take the II-V-I (in C, to keep it simple) Dmin7-G7-Cmaj7. using tritone substiution, you can replace the G7 with Db7. Now notice the basslines of all these notes: D-Db-C. A bit more modern sound.
Now on to making the melody more interesting. Take the chord progression Cmin7-F7-Bb7. Let's say that over the F7, you have the melody note G. This is the 9th of the F7 chord, a good note. If you want to make it more interesting, you could use tritone substitution and play B7. Now the melody note (G) is the #5 of the chord. Not only would you create a chromatic bass line, but you make the melody note more interesting.
(Note: some people might like the G to be the 9th, rather than the sharp 5th, which is fine. I'm just giving you an example.)
So to recap that long description:
Tritone subsitution is the substitution of a dominant chord with another dominant chord a tritone apart. To be used effectively, it should either create a chromatic bass line, or make the melody note more interesting.