I've just come back from my jazz workshop and the lines I played over a G7 C7 G7 D7#9 Eb7#9 D7#9b13 G7 progression were ok, -ish. When asked, our teacher told me to try dorian scales, over mixolydian and altered chords. What is your angle on this?
Common scales that "fit" the 7th chord include:
- Myxolydian (b7)
- Major pentatonic (1, 2, 3, 5, 6)
- Bebop (b7, natural 7)
- Lydian dominant (#4, b7)
- Whole tone
- Diminished (half, then whole steps)
- Diminished whole tone (b2, b3, b4, b5, b6, b7 - most common on "#9b13" chords)
If you haven't seen this video from the "Jazz Tutorials" channel, I would strongly suggest it. The Lydian Dominant scale emerges from the teacher's "chord tones + whole step" philosophy.
It's important to realize that not every scale that can theoretically be played over a dominant seventh chord is also a good choice in a specific musical context. In the case of the given progression the following scales are used in practice:
G7 G mixolydian C7 C mixolydian D7#9 D half-whole, D altered, D (minor) blues Eb7#9 Eb half-whole, Eb altered, Eb (minor) blues
Note that there's not a lot of time to play scales over the D7#9 and the Eb7#9 chords, so what people usually do is play (incomplete) arpeggios. As I've mentioned in a comment, you can learn a lot by analyzing the solos played by the greats. As an example, try to play an Fm7 arpeggio over D7#9, and a Gbm7 arpeggio over Eb7#9. In this way you'll play the 7, b9, #9, and the #11 of the respective chord.
It's also helpful to analyze the melody, and use it in your improvisations. The first thing that one notices it that over D7#9 the perfect fifth (A) as well as the #5 (b13) are used. Over Eb7#9 it's also the perfect fifth, not an altered fifth, that is used. This would imply the half-whole scale rather than the altered scale over these two chords. Another suitable choice matching the note choice of the melody over these two chords is the (minor) blues scale, which will give you the 5, 7, and #9.
You're not really asking the right question! It's taking a narrow, inward-looking, mechanical approach to a wide topic - how to play good jazz.
It's often a good idea to find a song using the chord sequence and see what the original melody was. That may well be the BEST thing to play over that sequence. And I bet is isn't just scales.