7F

7F or 7-F can refer to:

See also

Theoretical key

In music theory, a theoretical key or impossible key is a key and scale that exists in theory and practice, but whose corresponding key signature makes it impractical to notate. The key signature for such a key would contain one or more double-flats or double-sharps.

Double-flats and double-sharps indicate accidentals, but are never placed in the key signature (in music that uses equal temperament), due to notational convention, and because that would make reading the music difficult.

For example, the key of F♭ major is not conventionally used in notated music, because its corresponding key signature would contain a B (subdominant). An equal-tempered scale of F♭ major comprises the same notes as the E major scale. Under equal temperament the scales sound exactly the same; such key pairs are said to be enharmonically equivalent. So the theoretical key of F♭ major is usually practically notated by a key signature of E major.

The other option is to use either no key signature or one with single-flats and to provide accidentals as needed for the Bs.