Key signatures make it easy to produce uncluttered music score. The key signatue makes the use of naturally occurring sharps and flats in a scale redundant. Take a look at the F# major scale that does not use the key signature but rather deploys accidentals in the key.
Writing scales with & without key signatures
The scale of D flat major is written on the staff with key signature. The use of accidentals is not necessary when a key signatue is used at the beginning of a piece of music. Do note, however, keys may change in a piece of music. This depends on the composer.
Table of key signatures
Learn the table of key signatures to be able to easily recognise the key of any piece of music. The first table below tabulates the key signatures that have sharps. Major and minor scales share the same key signature. Example, the scale of G major has one sharp, F sharp. E minor, is the relative minor minor scale of G major and will therefore have one sharp, F sharp, as well.
How accidentals are used in music
Accidentals are used when a chromatic note is used in a diatonic key. Study the examples below for a clearer understanding of how accidentals are used. As we discussed in an earlier section, if the note does not belong in the diatonic scale it is chromatic. Do note however, that in the case of the harmonic and melodic minor scales, we only use accidentals for the altered notes. The accidentals will not form part of the key signature for the minor scale.
Ab harmonic minor scale - notice that the seventh note was raised from Gb to G natural to create a semitone interval between the 7th and 8th note.
Ab melodic minor scale - Fb and Gb are raised by a semitone each to F natural and G natural respectively to create the tonal structure for the melodic minor scale.
A# harmonic minor scale - The 7th note which is already G# has to raised by a semitone. It becomes G double sharp.
A# melodic minor scale - F# and G# are raised by a semitone each to F double sharp and G double sharp respectively to create the tonal structure for the A# melodic minor scale.