#1
I had a friend give me a quick rundown on chordal b5 substitution the other day, and it blew my mind. Can anyone else explain it to me again, and maybe include why it might work? Thanks.
#2
it's where you replace a dominant 7 chord with another dominant 7 chord a b5 interval in distance from it... otherwise known as the 'tritone substitution'

so, if you had G7, you would replace it with Db7

in other words, G B D F replaced with Db F Ab Cb

it works because they share the defining notes of B & F (enharmonically Cb & F)...

there's more to it than that, but that's the general overview
#3
Elaborating on what was said above: A tritone substitution works for the simple reason that an inverted tritone is a tritone. The defining tones of a dominant seventh chord are the 3rd and the b7, which give the chord its tonality and form the interval of a tritone. Because an inverted tritone is the same interval, a dominant seventh chord a tritone away behaves the same as the original dominant seventh chord.

Tritone substitutions are generally used in ii-V-I progressions because the new dominant seventh chord creates a chromatic movement towards the tonic (the progression could be described as: ii-bII7-I), which both sounds pleasing and strongly establishes tonality.
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#4
The tritone sub also gives an altered dominant sound. (b9b5)


G7 = GBDF
Db7 = Db F Ab Cb (b5 7 b9 3 as related to G7)
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#5
TS, everything above dude. Something extra, look at the V chord and the vii chord of the major scale. Take C major as per usual:

G7 and Bmin7b5.

They both share the tritone interval that is between F and B.
#6
in my quick overview of the reactions, i didn't see the important thing, ANY chord can be substituted with a tritone chord, and the color of the substitution does not go by rule but by ear, as joe pass has said so often

an example with the simplest of progressions, V - I in C minor could give
Gm7 - C#m7 - Cm7, where the tritone sub is just a m7 chord, but works as a lead in, which is as you might or might not know always ''theoratically allowed''
if you want a dominant sound in this, it's best to play Gm7 - C#7 - C7 - Cm7, where the tritone sub becomes more of a passing chord, and C7 is what it's really all about

so often the color of the next chord works just as good as a dominant chord, other colors are to be handled with care, so if you want more variation, use other dominant chords so the color still changes

anyway, as indicated before, play every kind of turn around with every kind of tritone substitution and you'll use it automatically where it sounds good
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Last edited by Funkicker at Aug 19, 2008,
#7
Quote by mdc
TS, everything above dude. Something extra, look at the V chord and the vii chord of the major scale. Take C major as per usual:

G7 and Bmin7b5.

They both share the tritone interval that is between F and B.


yep.... and to add to that...... Bmin7b5 = G9

B D F A ( 3 5 7 9 in relation to G)
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#8
Another thing to notice -- the tritone sub creates a chord who's root is a chromatic
half-step from the next chord. Chromatic root movement is strong. If you're
pondering doing a tritone sub, always look at the next chord. If it's a half-step
away from the sub, it's likely a good spot for a sub.