Chord sequence
A♭maj7 Adim7 B♭m7 E♭7
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 Ab major
All the chords
The I-VI-ii-V with a diminished 7th chord on #I in place of VI7, so the bass rises by half steps from I to ii.
Over Abmaj7 · Imaj7
The major scale and its modes are the most commonly used scales in western music.
Over Adim7 · ♯i°7
Mode 7 of Harmonic Minor
Over Bbm7 · ii7
Mode 2 of Major
Over Eb7 · V7
Mode 5 of Major