Theoretical key  From Wikipedia, the free encyclopedia Jump to:
navigation, search D minor, an impossible key signature. C
minor, equivalent possible key signature.  In music theory, a
theoretical key or impossible key is a key and scale which
exists in theory and practice, but whose corresponding key
signature make its notation impractical. Such a key is one whose
key signature would contain one or more double-flats or double-
sharps.  Double-flats and double-sharps are used in music as
accidentals, but they are never placed in the key signature (in
music that uses equal temperament), due to notational convention
and because reading the music would become unnecessarily
difficult.  For example, the key of D minor is not
conventionally used in notated music, because its corresponding
key signature would contain a Bdouble flat (submediant). An
equal-tempered scale of D minor comprises the same notes as the
C minor scale. Under equal temperament the scales sound exactly
the same; such key pairs are said to be enh