This seventh mode Altered Dominant Scale is one of the two true dominant scales found in MM, the other being built on the fourth scale degree and named "Lydian b7".
"But, what about the fifth mode", you say," the one with the tritone that has a 7b13 (aka Mixolydian b6)?" Well, OK, technically it is a dominant seventh chord, diatonic to MM and, like Major, sits on it's fifth mode, buttt!...........
Do you remember back in Pt. 1 when we surgically altered Major by lowering it's 3rd a half step, thus creating the MM scale? Well, one of the consequences of that move was, that by taking away the major third, we also took away a very important resolution, the Major V-I cadence.
In Major, the V7 chord is King! It ain't called "dominant" for nothin'. It sits up there on it's fifth position throne, ready to smoothly transform itself into a tonic or another dominant chord. In MM, however, it has been seriously demoted in importance, given a desk job, and used mostly as a tonic minor chord with the 5th in the bass. The reason being, once again, that MM is key and not cadence oriented. An MM V-i diatonic cadence is very weak, indeed, and therefore very rarely used.
So, the VII and the IV chords are the true dominants of MM, with the VII (altered scale) being the star of the show, when dealing with MM functional harmony. How each of MM's modes functions in a modal type situation would need to be the subject of a future post, or posts.
If you build a 7th chord from the seventh scale step of MM, you get (in C) B - D - F - A. Wait a minute, that's a min7b5 or half diminished, certainly not a dominant chord. But once again, back when we lowered that Maj. 3rd a half step, we created a diminished fourth relative to the 7th scale step (B-Eb), which sounds as a Maj. 3rd, thus creating an altered dominant scale and chord.
One of the more interesting techniques is one that employs not one, but several different MM scales in a Minor ii-V7-i cadence. This device has been around for a while, but is still, to my mind, under explored and very hip sounding.
As an example, if we were to play a ii-V7-i in C minor, we'd be dealing with Dmin7b5 / G7b9 / C min.
Since MM won't provide us with the either the b5 or the b9 (which is an Ab in both cases), we'll need to look elsewhere. Combinations of locrian (7th mode of Maj.), harmonic minor and MM are a decent choice. It worked pretty well for the early beboppers.
But, what somebody figured out along the way (I don't know where or when this originated, but I'd sure like to know), was that you could the use the vi mode of F Melodic Minor (Locrian #2) as the ii (Dmin 7b5, with a natural 9), and the seventh mode (altered scale) of Ab MM for the V (G7 altered). You could resolve it to either a tonic MM, or tonic Major or anything else.
If you notice, the distance between F MM and Ab MM is a minor 3rd. The root movement, however, is still a fourth up or a fifth down. The fact is, you don't even have to think of "mode' here, just the MM keys you'll be using for the ii & V. It takes a bit of practice and memorization of the MM scale pairs for the ii & V, but it will add a whole new chapter to your improv vocabulary.
........And now for the freebies!
This exercise illustrates the flexibility of MM harmony because of the absence of any avoid notes.
I broke the rhythm up to make it a little more interesting, but it sounds pretty cool when you play it straight, too.