Key signature may consist of one or more sharps combined with one or more flats (such as a signature containing both F and B). Key signatures of this kind can be found in the music of Béla Bartók, for example. The effect of a key signature continues throughout a piece or movement, unless explicitly cancelled by another key signature. For example, if a five-sharp key signature is placed at the beginning of a piece, every A in the piece in any octave will be played as A sharp, unless preceded by an accidental (for instance, the A in scale 2 illustrated –
Theoretical key G♯ major) may have to be notated completely differently. Theoretical key In music theory, a theoretical key or impossible key is a key whose key signature has at least one double-flat or double-sharp. Double-flats and double-sharps are often used as accidentals, but placing them in the key signature (in music that uses equal temperament) makes the music generally impractical to read. For example, the key of G major is a key of this type, because its corresponding key signature has an F (on its leading-tone). An equal-tempered scale of G major comprises the same pitches as the A major scale,