
Accidental across clef changes
The clef changes from bass to treble and then back to bass. When this happens, does the B-flat carry over? In other words, even in the treble clef and later when returning to the bass clef, should all B's still be played as B-flat, even if the flat sign isn't written again?
The piece is in F Major—Sonatina in F Major, Op. 168 No. 1 by Diabelli.
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Of course. The flat symbol is written at the beginning of the staff on B and not in front of a note. This means it is a key signature (in this case F major or d minor) and it is valid until replaced by another key signature. — If, however a flat is written immediately in front of a note B within a bar, then all B's (same octave) in that bar are B-flats. In the next bar the B is natural again.
So:
Accidentals (flats, sharps, naturals etc.) at the beginning of a staff, right behind the clef, come in fixed combinations and indicate a key signature. They tell you to play that note half a tone higher or lower and it applies to that note in all octaves.
Accidentals in front of a particular note are valid only for that note in that octave and that bar. It applies to that particular note irrespective of whether you repeat it in different clefs.