Scale is a choosen set of tones within an octave. It is defined by distances between the tones (scale degrees). Most used scale is major scale. Its structure is: (WT - whole tone, ST - semitone):
To start the scale with another tone along with preserving the scale structure we must use accidentals. E.g. G major scale (starting at G) has one accidental F#. D major scale has two accidentals (F# and C#):
The scale starting at 5. degree of current scale has one sharp accidental more. E.g. in G major scale is the fifth degree note D. It means D major scale has two sharp instead of one.
Accidentals can be grouped in a key signature which is valid for the whole tune. Key signatures for major scales with sharps:
Similarly for scale with flats - the number of flats increases by one if we start next scale at 4. scale degree.
Key signatures of all major scales can be put in circle of fifth. Fifth refers to the distance between first and fifth scale degree of major scale. Notes in circle of fifth are shifted by a fifth in clockwise direction. Additionally the notes are shifted by a fourth (fourth scale degree) in the counterclockwise direction. Therefore it is sometimes refered as circle of fourth.
Practice key signatures in our