B♭ (musical note)

B♭ (B-flat; also called si bémol) 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♯ although in some musical tunings, B♭ will have a different sounding pitch than A♯. B-flat is also enharmonic to C.

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. See pitch (music) for a discussion of historical variations in frequency.

While orchestras tune to an A provided by the oboist, wind ensembles usually tune to a B-flat provided by a tuba, horn, or clarinet.

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