This is a quick recap about how to approach improvisation over altered dominant chords. Altered dominant chords will be dominant chords with one of the following tensions: b9, #9, b5, #5.
Recall that we can play the Altered Scale (the seventh mode of Melodic Minor) over altered dominant chords. See this post for more details on that mode. To recap, the Altered Scale has the following intervals:
R – b2 – b3 – b4 – b5 – b6 – b7
So what chord tones could we emphasise when improvising over an altered dominant?
You could naively – and incorrectly – interpret the intervals of the Altered Scale to suggest that you can target the following intervals as chord tones:
R - b3 - b5 - b7
That would be wrong!
In effect that would be like targeting the chord tones of a m7b5. Remember we are actually playing over an altered dominant chord. Dominant chords have a major 3rd (3) and a flat 7 (b7). The Altered Scale doesn’t have a major 3rd but it does have a flattened 4th (b4) which is actually the same interval as a major 3rd. So, to accentuate the dominant flavour of the chord we can target the following intervals:
R - b4 - b7
We can then accentuate the appropriate tension tones as well:
b9 - #9 - b5 - #5
If we compare the tension tones to the Altered Scale we find that the b9 is the same as a b2, the #9 is equivalent to a b3, the b5 is already in the Altered Scale, and the #5 is equivalent to a b6. So, the tensions are available in the Altered Scale as:
b2 - b3 - b5 - b6