B flat

musical note which is one half-step lower than a B

La Dièse or A♯ (A sharp) is the eleventh semitone of the solfege.It lies one half of a tone above A and one half of a tone below B, thus being enharmonic to Si Bémol or B♭ (B flat).When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of the A♯ semitone is approximately 466.164 Hz. See pitch (music) for a discussion of historical variations in frequency.
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Also see: B-flat minor, or B major. B-flat major is a major scale based on B-flat, consisting of the pitches B-flat, C, D, E-flat, F, G, A and B-flat. Its key signature has two flats, B/E (see below: Scales and keys). [The note B-flat is a half-tone between A & B.]Its relative minor is G minor, and its parallel minor is B flat minor.B-flat major is a suitable key for most wind instruments, especially those for which it is their home key, such as clarinets, trumpets, and saxophones in B-flat.
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SI BEMOLLE