As each year passes, the music which comes under the heading of "Rock" contains more variety. In one performance, a Rock band may include songs which cover elements of Rock and Roll, Grunge, Pop, Blues, Ballads, Swing, Soul, and Hip-hop. The way each song is delivered depends on what is most appropriate for the style. For example, perfectly correct grammar can often sound out of place in a Rock or Blues song, as songs in these styles are based on a language tradition which has always included slang.
The vocal sound used for different styles also varies tremendously. When singing a hard Rock or Blues number, a singer will generally use a much rougher sound than they would use for a ballad.