Chord sequence
A♭m7 Fm7♭5 B♭m7♭5 A7♯11
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 minor
Over Abm7 · i7
Mode 2 of Major
Over Fm7b5 · viø7
Mode 7 of Major
Over Bbm7b5 · iiø7
Over A7#11 · subV7♯11
Mode 4 of Melodic Minor