B minor
In medieval music, the B molle ( Latin for 'soft b') denotes the lower variant of the note b, which was used in the Hexachordum molle built on f , in contrast to the higher B durum of the Hexachordum durum, which starts from g .
The for the molle B characters used, the B rotundum (Latin for, round B ') is in the square notation of Neumen an offset mark to indicate the lowering of a tone by a semitone . It applies to the entire length of the word sung in a Gregorian chant and can be canceled within this by a B major . At first it was only used in connection with the tone b , but later also with other tones.
The accidental ♭ in modern musical notation is reminiscent of the b minor .