 Director Brian Helgeland (qv) once said in an interview that he  had a simple explanation for the use of modern music in the movie.  He said that he felt it would show people today what people then  felt about their music. When true Renaissance music is used in  movies today it fails to convey the emotional response that people  back then had to such music. Helgeland used modern music to try to  elicit an emotional response in the movie audience akin to what  medieval people would have felt when hearing the music of that time.