In traditional Western music, the key is the tonal center of a
composition. The choice of key determines which of the other
notes in the scale will be considered "natural". The Western
scale divides the octave into twelve notes (plus the octave, at
double the frequency of the lowest note). Any given key uses
eight of these, or seven plus the octave, from which the
composer can construct melodies and harmonies. Since many times
the judicious use of the other five notes, also known as
chromaticism, will make the music more compelling, we have
notation devices to indicate when they are used instead of their
natural counterparts. A piece of music will also often change
keys at various times, known as modulation. This is usually done
by moving to a closely related key, that is, one whose key
signature only differs by one sharp or flat in either direction.
An easy way to find which keys are related in this way is to
follow the circle of fifths. The notes used in the key of C
major (corresponding to the white notes