 Classically, a rock band takes the form of a quartet whose members cover one or more roles, including vocalist, lead guitarist, rhythm guitarist, bass guitarist, drummer, and often keyboard player or other instrumentalist.Rock music is traditionally built on a foundation of simple unsyncopated rhythms in a 4/4 meter, with a repetitive snare drum back beat on beats two and four.Melodies often originate from older musical modes such as the Dorian and Mixolydian, as well as major and minor modes.