Space plays and stops
- Notes and intervals
- B#m3D#m3F#m3A
B# Diminished 7, written B#dim7, is built from B#, D#, F# and A: the root, minor 3rd, flat 5th and diminished 7th.
Its 3rd and 7th, D# and A, are its guide tones: they say what kind of chord it is, so voicings are built around them and the root is often left to the bass.
In the progressions here, B#dim7 is the ♯i°7 of the Diminished Passing Turnaround in B and the ♯iv°7 of the Jazz Blues in F#.