Scruffles
04-13-2006, 03:10 PM
Well, one way to make a chord progression more interesting is to apply tritone substitution on the V7 chord. This means that you simply utilize the root a tritone away. The most important notes of a 7 chord are the third and seventh--in a dominant seventh chord, there is a major third and a minor seventh, which are separated by a tritone between both the third and seventh and the seventh and third. If you use the root a tritone away, the third and seventh remain the same, only their functions are inverted. For example, D7 is spelled D F# A C, and the third and seventh are F# and C, respectively. A tritone away from D is Ab. The notes in an Ab7 chord are Ab C Eb Gb, and the third and seventh are C and Gb, respectively, and Gb is enharmonic to F#. Tritone substitution is useful because it can create a descending chromatic bassline in a ii-V-I progression. Here's an example in C major:
||: Dm7 | G7 | Cmaj7 | % :||
Using tritone substitution, we get:
||: Dm7 | Db7 | Cmaj7 | % :||
Well, the thing is, although the third and seventh remain the same other than the fact that their functions switch, they are still spelled enharmonically. For example, the third and seventh in E7 are G# and D, and the third and seventh in Bb7 (a tritone away) are D and Ab. Ab and G# are the same note enharmonically, but they are spelled differently--Ab is the minor seventh in the key of Bb, and G# is the augmented sixth. To get the Ab to be spelled as a G+, you must use an augmented sixth chord. This renders the spelling 1 3 5 #6, which is Bb D F G# in the key of Bb. These are called German augmented sixth chords, and will resolve down a half step. They are enharmonic to a dominant seventh with the same root (1 3 5 b7).
Another type of augmented sixth chord is the Italian augmented sixth chord. Their spelling is 1 3 #6. They are enharmonic to a dominant seventh chord with an omitted fifth with the same root (1 3 b7).
The last type of augmented sixth chord is the French augmented sixth chord. Their spelling is 1 3 #4 #6. They are enharmonic to 7b5 chords with the same root (1 3 b5 b7). So, to correctly notate the aforementioned progression, we would have to use an augmented sixth chord:
|| Dm7 | Db+6 | Cmaj7 | % ||
Now, dominant seventh chords resolve down a fifth and augmented sixth chords resolve down a half step. Both chords are enharmonic, so a chord can be approached as a dominant seventh and quit as an augmented sixth or vice versa. This allows you to modulate down a tritone, and the process is known as enharmonic substitution. Here's that same progression in C major, but this time, the Db+6 will be quit as a Db7, therefore resolving to Gbmaj7:
|| Dm7 | Db+6 | Gbmaj7 | % ||
If you approach a chord as a dominant seventh and quit it as an augmented sixth, you can get a result like this (also starting in C major):
|| Dm7 | G7 | F#maj7 | % ||
||: Dm7 | G7 | Cmaj7 | % :||
Using tritone substitution, we get:
||: Dm7 | Db7 | Cmaj7 | % :||
Well, the thing is, although the third and seventh remain the same other than the fact that their functions switch, they are still spelled enharmonically. For example, the third and seventh in E7 are G# and D, and the third and seventh in Bb7 (a tritone away) are D and Ab. Ab and G# are the same note enharmonically, but they are spelled differently--Ab is the minor seventh in the key of Bb, and G# is the augmented sixth. To get the Ab to be spelled as a G+, you must use an augmented sixth chord. This renders the spelling 1 3 5 #6, which is Bb D F G# in the key of Bb. These are called German augmented sixth chords, and will resolve down a half step. They are enharmonic to a dominant seventh with the same root (1 3 5 b7).
Another type of augmented sixth chord is the Italian augmented sixth chord. Their spelling is 1 3 #6. They are enharmonic to a dominant seventh chord with an omitted fifth with the same root (1 3 b7).
The last type of augmented sixth chord is the French augmented sixth chord. Their spelling is 1 3 #4 #6. They are enharmonic to 7b5 chords with the same root (1 3 b5 b7). So, to correctly notate the aforementioned progression, we would have to use an augmented sixth chord:
|| Dm7 | Db+6 | Cmaj7 | % ||
Now, dominant seventh chords resolve down a fifth and augmented sixth chords resolve down a half step. Both chords are enharmonic, so a chord can be approached as a dominant seventh and quit as an augmented sixth or vice versa. This allows you to modulate down a tritone, and the process is known as enharmonic substitution. Here's that same progression in C major, but this time, the Db+6 will be quit as a Db7, therefore resolving to Gbmaj7:
|| Dm7 | Db+6 | Gbmaj7 | % ||
If you approach a chord as a dominant seventh and quit it as an augmented sixth, you can get a result like this (also starting in C major):
|| Dm7 | G7 | F#maj7 | % ||