A♯ (musical note)

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A (A-sharp) or La Dièse is the eleventh semitone of the solfege.

It lies a chromatic semitone above A and a diatonic semitone 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.