Chord and FretBb7(b5) — dominant seventh flat five
Also written A#7(b5) — the same chord, spelled the other way.
Notes in Bb7(b5): Bb – D – Fb – AbFormula: 1 – 3 – b5 – b7In the formula, the numbers count steps of the major scale starting from the note that names the chord; "b" lowers a half step, "#" raises one — and a slash names the bass note.
Here the fifth drops a semitone and the chord turns ambiguous on purpose: the same four notes serve two distant dominants (C7(b5) and F#7(b5)). That coincidence is the door to the tritone substitution.
The same chord on all four instruments
Where to use it: Jazz, bossa and turnarounds — the natural step toward swapping one dominant for another.
Every region of the neck hides more shapes of Bb7(b5). In Chord and Fret, you hear every shape strummed string by string, in each instrument's own voice; compare positions with their difficulty marked; and set a capo — the diagrams redraw above it. Start free. Unlock everything with Pro. Plays offline.
See the whole neck in Chord and Fret →Part of the Sevenths family.