Chord sequence
Am7 F♯m7♭5 Bm7♭5 B♭7♯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 A minor
Over Am7 · i7
Mode 2 of Major
Over F#m7b5 · viø7
Mode 7 of Major
Over Bm7b5 · iiø7
Over Bb7#11 · subV7♯11
Mode 4 of Melodic Minor