Key Signature

key-signature-thumb
Determining the Key

The key signature is placed after the time signature indicating the key or pitch range of the scaling system for the appropriate instrument with a series of sharp or flat signs. Depending upon the key, the signature could contain one or several sharp or flat symbols. See also Enharmonic & Diatonic for key breakdown, assignment, and reference.

Key Marks & Accidentals
Key Marks, also called Accidentals or Key Symbols are placed next to the note when changing its pitch during the composition. The natural key symbol is never used in the key signature. Illustrated below are the key marks.
natural
The natural sign is used as an accidental during the composition to change a sharp or flat note back to its natural pitch.
demisharp
The demi-sharp sign is used as an accidental during a composition to augment the pitch of a note by one-quarter step.
sharp
The sharp sign is used in the key signature to indicate which notes are sharp in the composition as well as the key of the instrument used for the music. The sharp sign is used as an accidental during a composition to augment the pitch of a note by one-half step.
sharp-double
The double-sharp sign is used as an accidental during a composition to augment the pitch of a note by one step.
sharp-and-half-sesquisharp
The sesquisharp or sharp-and-a-half sign is used as an accidental during a composition to increase the pitch of a note by three quarter-steps.
demiflat
The demiflat sign is used as an accidental during a composition to diminish the pitch of a note by one-quarter step.
flat
The flat sign is used in the key signature to indicate which notes are flat in the composition as well as the key of the instrument used for the music. The flat sign is used as an accidental during a composition to diminish a note's pitch by one-half step.
flat-double
The double-flat sign is used as an accidental during a composition to diminish the pitch of a note by one step.
sesquiflat-flat-n-half
flat-and-a-half
The sesquiflat or flat-and-a-half sign is used as an accidental during a composition to diminish the pitch of a note by three quarter-steps. A slashed double-flat is also used as a flat-and-a-half sign.