The F and B over a G bass is called the Tritone.

The 3 and the dom7 of the chord.

Since the Tritone is exactly halfway between octaves, each Tritone can function as the Shell of two different dom7 chords a flat five apart.

That F and B over G can also be played over Db and becomes the Db Tritone. Notice how the 7 and 3 invert when you do that.


--Mac