Flat Signs
This is a flat sign.
When a flat sign is placed in front of a note, it lowers the pitch of the note by an interval known as one semitone or one half step. Thus the note Bb is one semitone lower than B.
Since the difference in pitch between the notes A and B is one whole tone (two semitones or one whole step), Bb is also one semitone higher than A.
The Note Bb
A flat sign is always placed before the note.
Like the sharp sign, the flat sign affects all B notes within the bar in which it appears. E.g.: in bars 1, 3 and 5 the b sign appears before the first B in each bar. The flat also applies to all other B notes within that particular bar. The effect of a flat sign is cancelled by a bar line, meaning that a new flat sign is needed to indicate a new Bb note in the following bar.
