A♯ (A-sharp), or La Dièse, is the eleventh semitone of the solfege. This note 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♯ above middle C is approximately 466.164 Hz. See pitch (music) for a discussion of historical variations in frequency.