Key Signatures

When one or more sharps or flats appear directly after the clef sign, they constitute a 'key signature'. In this case the lines or spaces in which these sharps or flats occur show which notes are to be raised or lowered by a half tone throughout the entire piece of music.

Note: # denotes a sharp.

Denotes a key of G. All F's are sharp.
Denotes a key of D. All F's and C's are sharp.
Denotes a key of A. All F's, C's and G's are sharp.
Denotes a key of E. All F's, C's, G's and D's are sharp.
Denotes a key of B. All F's, C's, G's, D's, and A's are sharp.
Denotes a key of F#. All F's, C's, G's, D's, A's and E's are sharp.
Denotes a key of C#. All F's, C's, G's, D's, A's, E's and B's are sharp.

Denotes a key of F. All B's are flat.
Denotes a key of B flat. All B's and E's are flat.
Denotes a key of A. All F's, C's and G's are sharp.
Denotes a key of E. All F's, C's, G's and D's are sharp.
Denotes a key of B. All F's, C's, G's, D's, and A's are sharp.

Note:
E# is the same as F.
F flat is the same as E.
B# is the same as C.
C flat is the same as B.

Therefore, a key of A major employs the scale of A-B-C#-D-E-F#-G#; since F sharp, G sharp and C sharp are normal notes within the key, the key signature for A major is C#-F#-G#. The same key signature is used for the relative minor of A major, that being F sharp minor.

Modulation and temporary employment of another key do not necessarily involve change of key signature. Alternations can be indicated by Accidentals. Accidentals are signs in front of notes which modify the pitch chromatically. In this way one may define notes which are not part of the scale as defined by the key signature. The following signs are accidentals:
(Sharp)
(Flat)
(Natural)
(Double sharp)
(Double flat)

Accidentals modify the pitch of a note and remain in force until the end of a bar, or until negated by another accidental on a note of the same pitch (which may signal a return to the diatonic pitch).

A sharp or flat that is written in directly before a note is effective for the remainder of the measure. This kind of sharp or flat, or one appearing as part of a key signature, can be cancelled by a symbol called a 'natural'.

For Example:

The first note, an F natural will cancel the F# that is part of the G major key. The F natural will remain for the whole of the first bar only. The second bar shows how we can explicitly reverse the natural back to the original key of G major for the remainer of the bar.

The key signature of a music piece is repeated at the beginning of each stave and remains in force until a new key signature is indicated (usually proceeded by a double bar).

David Webber 1994-96. Mozart Music Generator Program
Jimmy Dorsey, Saxophone Method, A School of Rhythmic Saxophone Playing
Concise Dictionary of Music, 1986.

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