okay, I've been wondering something
If you are playing a chord, and then mess with something in the bass, for example, throw in a tri-tone, what is the naming convention for that newly formed chord?
For example, lets say, in the key of C, you play
(LH/RH)
C / G - C - E C major
but then put a tri-tone in the bassas a setup for a new chord, like this:
D - Ab / G - C - E
what would you call that? Is it still a C chord, in which case you would start naming it by identifying the C as the root
First, when figuring out chords, when only one tritone is involved, it will usually be between the root and 5th or the 3rd and 7th since the tritone is integral to the dominant chord and its derivatives. It could surely be named in a way that puts the tritone between higher members, but it will try to function as if the tritone has a closer relationship to the root.
In this instance, your tritone can belong to Bb7, Dm7b5, D dim, E7, G#m7b5, or Gdim
[The () means an implied note. The / in the note names is alternate spellings]
Bb7 -- (Bb) D (F) Ab C E G --- Bb7 9/#11/13
The Dm7b5 (half-diminished 7) is simply the notes of the Bb 9 without a root.
E7 -- E G#/Ab B#/C D F##/G (A) C --- E7 #5/#9
This is actually a rootless voicing that allows either chord. (two chords for the price of one). The potential root would have to be determined according to the key and the context of the chords around it. If the key is Eb, Bb7 is its dominant and E7 is the tritone substitute. If there is no compelling reason to indicate a Bass of E, then the Bb name is the choice. (In A -- E7 is Dominant and Bb7 is tritone sub)
If the Bass motion has been by steps and half-steps then the choice that continues that motion may be the better choice. In the key of Eb Say the bass line has been moving down "A Ab G Gb F (?) Eb" Then E might be the better choice (unless you want to break the pattern.) On the other hand, if the bass has been moving "D G C F (?) Eb" Then the Bb choice may be better.
With these types of chords, there is really no hard and fast rule.
Either way, they are tritone substitutes other.