The sound of rock

The sound of rock is traditionally centered around the electric guitar, which emerged in its modern form in the 1950s with the popularization of rock and roll. The sound of the electric guitar in rock music is typically supported by the electric bass guitar pioneered in jazz music in the same era, and percussion produced from a drum kit that combines drums and cymbals. This trio of instruments has often been complemented by the inclusion of others, particularly keyboards such as the piano, Hammond organ and synthesizers.A group of musicians performing rock music is termed a rock band or rock group and typically consists of between two and five members. 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 occasionally that of 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 are often derived from older musical modes, including the Dorian and Mixolydian, as well as major and minor modes. Harmonies range from the common triad to parallel fourths and fifths and dissonant harmonic progressions. Rock songs from the mid-1960s onwards often used the verse-chorus structure derived from blues and folk music, but there has been considerable variation from this model. Critics have stressed the eclecticism and stylistic diversity of rock.Because of its complex history and tendency to borrow from other musical and cultural forms, it has been argued that "it is impossible to bind rock music to a rigidly delineated musical definition."