AS a point of possible interest, a fine old banjo picker (Rufus Crisp by name) once explained to me that he had filed the frets down flush to the fingerboard on his banjo because, otherwise, he fouldn't play the "right: notes. On t'other hand, I really can't envision musicians who play larger instruments (like pianos or even guitars) carrying a separate instrument for each key they wished to play in. There are practical considerations.