[PD] pd-based procedural chord progression database..

[Chuckk Hubbard]

On 8/13/06, patco <megalegoland at yahoo.fr> wrote:
>
>
> padawan12 <padawan12 at obiwannabe.co.uk> a écrit :
>
> >What is a tri-tonic substitution?
>
> The seventh flat in a major chord is the triton of the major third, if we
> substitute a 7 flat major chords with another one, _six semi-tones below_,
> or above (same one), we will get the same notes than the altered chord.
> The altered chord is often used instead of the 7 flat major chord for
> resolving
> to the major chord or a minor chord one fift above.

One explanation I heard is that the V7-I progression is strong
partially because the tritone between the IV and vii in the V7 chord
resolves outward to iii and I.  Like Patco says, that same tritone is
present in the 7th chord a tritone away.
So if, instead of
Am    | D7    | GMaj7
you play
Am    | Ab7  | GMaj7
The progression still sounds pretty compelling.  Long ago, jazz
players got bored with this, and, wanting more of a good thing,
experimented with substituting just about every chord in any
progression with a chord a tritone away.  A 3-6-2-5-1 progression
becomes a chromatically descending progression if you replace 6 and 5
with flat 3 and flat 2.
Rather than list the possibilities for using tritone subs, it's
simpler to list the times when they're avoided.  They're never
avoided.

-Chuckk