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accidentals 
Signs used to change the pitch of a note.
key signature
Collective term for the accidentals placed after the clef to indicate the tonality of a composition.
sharp
Accidental placed before a note that raises it by a semitone.
natural
Accidental that cancels the effect of another accidental.
double flat
Accidental placed before a note that lowers it by two semitones.
double sharp
Accidental placed before a note that raises it by two semitones.
flat
Accidental placed before a note that lowers it by a semitone.
