Simple classical pieces and plenty of pop and traditional music songs are written so that all the music is in a single key. More advanced Classical, pop and conventional music songs and items may have two keys . Classical music from the Romantic period (written from about 1820–1900) usually incorporates multiple keys, as does jazz, particularly Bebop jazz from the Nineteen Forties, during which the important thing or “residence notice” of a music may change each 4 bars and even each two bars. In the 2000s, notated music is produced as sheet music or, for people with pc scorewriter applications, …