As the single-flat lowers a note by a half-tone, so a double-flat lowers it by two half-tones or a full tone.
Double Sharp Misprinted for Double Flat
In playing an operetta recently I found the double-sharp sign [X] used for double-flats as well. Is this correct?
The sign may be a misprint. But if it should occur repeatedly I advise you to make quite sure, before taking the misprint for granted, that the sign is not, after all, meant for a double-sharp.
When an Accidental Is in Parentheses
Please tell me how a chord or an interval marked thus, is executed.
What does an accidental in parentheses mean?
Chords marked as above are slightly rolled in the same manner as if marked by a serpentine line, unless the sign denotes a linking with the other hand. Which of the two meanings is intended you will easily infer from the context. Accidentals in parentheses are mere warnings given by some composers wherever there is a possibility of doubt as to the correct reading caused by a momentary harmonic ambiguity. I have found these accidentals in parentheses so far only in the works of French composers.
The Staffs Are Independent of Each Other