Chord sequence
A♭m7 C♯7 Am7 D7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in G major
Chords 1 to 2
Abm7 C#7
Chords 3 to 4
Am7 D7
Over Abm7 · ♭ii7
Mode 6 of Blues
Over C#7 · V7/vii
Over Am7 · ii7
Mode 2 of Major
Over D7 · V7
Mode 5 of Major