B durum
In medieval music, the B durum ( Latin for 'hard b') denotes the higher variant of the note b, which was used in the Hexachordum durum built on g , in contrast to the lower B molle of the Hexachordum molle, which starts from f .
The for B durum used character b quadratum (Latin for, square b ') is, in the square notation of Neumen a natural sign , the lowering of a tone by a semitone cancels. It applies to the entire length of the word sung in a Gregorian chant and can be canceled within this by a new B minor . At first it was only used in connection with the tone b , but later also used with other tones.
In modern musical notation , the b quadratum corresponds to the natural symbol ♮, which is also used there . The cross ♯ also developed from the b durum .