Chord sequence
A♭m7 D♭7 G♭m7 C♭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 Fb major
All the chords
The I-VI-ii-V turnaround with iii, which shares three notes with the I chord, standing in for the tonic.
Over Abm7 · iii7
Mode 6 of Major
Over Db7 · V7/ii
Mode 5 of Melodic Minor
Over Gbm7 · ii7
Mode 2 of Major
Over Cb7 · V7
Mode 5 of Major