a 4/4 meter, with a repetitive snare drum back
beat on beats two and four. Guitar solos feature prominently in rock music; however, keyboard, saxophone and blues-style harmonica are also sometimes used as soloing instruments. In its "purest form", it "has three chords, a strong, insistent back beat, and a catchy melody. Rock music is a genre of popular music that developed during and after the 1960s. It has its roots in 1940s and 1950s rock and roll, rhythm and blues, country music and also drew on folk music, jazz and classical music. The sound of rock often revolves around the electric guitar, bass guitar, drums, and keyboard instruments such as Hammond organ, piano, or, since the late 60s, synthesizers.