Overall Rating: 5.0 (of 5)
Tritone Substitution Intro
I am no Jazz expert but thus far, Tritone Sub is one of my favorite theoretic concepts I've learned. My issue with walking bass has always been that there does not to seem to be too many options for lines; it's always arpeggios or scales up and down with a few chromatics thrown in hear or there. Tritone Sub, in my opinion, can double the amount of lines you can use when walking.
In jazz, in music in general really, the strongest tones of the arpeggio are the 3rd and the 7th. They are the ones that really give the shape to the chord. The root does too, to some extent (it's more for showing "where" the chord is if that makes sense), but we all know how boring JUST roots are. And the same goes for roots and fifths. Not even bossa players play just roots and fifths all the time, because thats boring.
This being said, lets look at a Dominant chord. Bb7 for example. It is formed with a Bb (root), D(iii) , F(V), and Ab(b7). Let's forget about those boring root and fifth for a second and think about the 3rd and the 7. D and Ab. Hmmm... is Bb7 the only 7th chord with those two as the 3 and 7 (not necessarily in that order)? I'll give you a hint: no. E7: E (R) Ab(iii [gasp]) B(V) and... bum ba bum! D as the b7.
That being said, since the Bb7 & E7 have similar shapes, thanks to sharing the strong tones, why not try to substitute one for the other, for a bit of extra tension? I mean, it's a b5 to what would normally be the chord at the given time. On the next few pages are a few examples.