by Chris Tarry
Because the tritone occurs only in a dominant chord, it is what really gives the dominant chord it's sound. It has that sound or feeling like it wants to move to another chord.
Take a look at any dominant 7th chord. Ok, how bout' C7. Take a look at the 3rd (E) and 7th (Bb) of this chord. Notice anything..I'll wait....
The Bb and E are also the 3rd and 7th of another dominant chord. That would be F#7. Because the tritones are the same you can substitute these chords for one-another.
So some classic tritone sub's would be in a standard II-V-I
D-7 G7 Cmaj7 would become D-7 Db7 Cmaj7
You as the bass player can use these where ever you feel inclined. It can work great in adding an extra weapon in creating interesting walking bass lines.
In the example below, check out how I have the backing track playing a standard II-V-I in Bb with a the typical bass line the first time. After that, I switch it so the track is still playing the standard II-V-I but the bass hints at the tritone substitution.
Hope you enjoy!