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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♯, even though 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.
In Germany, Russia, Poland and Scandinavia, this pitch is designated B, with 'H' used to designate the B-natural. Since the 1990s, B-flat is often denoted Bb or "Bess" instead of B in Swedish music textbooks. Natural B is called B by Swedish jazz and pop musicians, but still denoted H in classical music. See B (musical note) for an explanation.
|Scientific designation||Helmholtz designation||Octave name||Frequency (Hz)|
|B♭-1||B♭ or B♭ or BBBB♭||Subsubcontra||14.568|
|B♭0||B♭ or B♭ or BBB♭||Subcontra||29.135|
|B♭1||B♭? or ?B♭ or BB♭||Contra||58.270|