Chord sequence
G♭7 C♭7 G♭7 C♭7 G♭7 D♭7 C♭7 G♭7 D♭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 Gb major
All the chords
The 12-bar blues in its simplest form, with dominant 7th chords on I, IV and V; the most commonly played progression in jazz.
Over Gb7 · V7/IV
Mode 5 of Major
Over Cb7 · IV7
Mode 4 of Melodic Minor
Over Gb7 · I7
Over Db7 · V7