B♭

B♭ is the eleventh step of the Western chromatic scale (starting from C). It lies a diatonic semitone above A and a chromatic semitone below B, thus being enharmonic to A♯, even though in some musical tunings, B♭  will have a different sounding pitch than A♯. B♭ is also enharmonic to C double flat. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of the B♭ above middle C is approximately 466.164 Hz. 

Common scales beginning on B♭

B-flat major: B♭ C D E♭ F G A B♭

B-flat natural minor: B♭ C D♭ E♭ F G♭ A♭ B♭

B-flat harmonic minor: B♭ C D♭ E♭ F G♭ A B♭

B-flat melodic minor ascending: B♭ C D♭ E♭ F G A B♭

B-flat melodic minor descending: B♭ A♭ G♭ F E♭ D♭ C B♭

Diatonic scales

B♭ Ionian: B♭ C D E♭ F G A B♭

B♭ Dorian: B♭ C D♭ E♭ F G A♭ B♭

B♭ Phrygian: B♭ C♭ D♭ E♭ F G♭ A♭ B♭

B♭ Lydian: B♭ C D E F G A B♭

B♭ Mixolydian: B♭ C D E♭ F G A♭ B♭

B♭ Aeolian: B♭ C D♭ E♭ F G♭ A♭ B♭

B♭ Locrian: B♭ C♭ D♭ E♭ F♭ G♭ A♭ B♭

Jazz melodic minor

B♭ ascending melodic minor: B♭ C D♭ E♭ F G A B♭

B♭ Dorian ♭2: B♭ C♭ D♭ E♭ F G A♭ B♭

B♭ Lydian augmented: B♭ C D E F♯ G A B♭

B♭ Lydian dominant: B♭ C D E F G A♭ B♭

B♭ Mixolydian ♭6: B♭ C D E♭ F G♭ A♭ B♭

B♭ Locrian ♮2: B♭ C D♭ E♭ F♭ G♭ A♭ B♭

B♭ altered: B♭ C♭ D♭ Edouble flat F♭ G♭ A♭ B♭