Double sharps, double flats and enharmonic notes

Double sharps and double flats

• A double sharp (a sign like a small x) raises a note two semitones: F double sharp sounds the same as G.
• A double flat (two flat signs) lowers a note two semitones: B double flat sounds the same as A.

To cancel one, write a natural. To go from a double sharp back to a single sharp, write the single sharp.

An accidental lasts until the end of the bar for that note at that pitch, unless another accidental, such as a natural, cancels it. The next barline cancels it, but a note tied across the barline keeps it.