I Introduction Rock Music, group of related music styles that have dominated popular music in the West since about 1955. Rock music began in the United States, but it has influenced and in turn been shaped by a broad field of cultures and musical traditions, including gospel music, the blues, country-and-western music, classical music (see Music, Western), folk music, electronic music, and the popular music of Asia, Africa, and Latin America (see Worldbeat). In addition to its use as a broad designation, the term rock music commonly refers to music styles after 1959 predominantly influenced by white musicians. Other major rock-music styles include rock and roll (also known as rock 'n' roll), the first genre of the music; and rhythm-and-blues music (R&B), influenced mainly by black American musicians (see African American Music). Each of these major genres encompasses a variety of substyles, such as heavy metal, punk, alternative, and grunge. While innovations in rock music have often occurred in regional centers—such as New York City; Kingston, Jamaica; and Liverpool, England—the influence of rock music is now felt worldwide. II Musical Elements The central musical instrument in most kinds of rock music is the electric guitar. Important figures in the history of this instrument include jazz musician Charlie Christian, who in the late 1930s was one of the first to play the amplified guitar as a solo instrument; Other instruments commonly used in rock music include the electric bass guitar keyboard instruments such as the electric piano, organ, and synthesizer; and the drum set, an Instruments that play important roles in certain rock-music genres include the saxophone—prominent in jazz-rock and soul music—and a wide assortment of traditional instruments used in worldbeat music. The microphone also functions as a musical instrument for many rock singers, who rely upon the amplification and various effects (such as echo) obtainable through electronic means. Rock music also shares more complex technical aspects. Most rock music is based on the same harmonies as Western music, especially the chords known as tonic, subdominant, and dominant The musical form of rock music varies. Rock and roll of the late 1950s relied heavily upon 12-bar blues and 32-bar song forms. Some rock bands of the late 1960s experimented with more flexible, open-ended forms, and some rock bands of the 1970s developed suite forms derived from classical music. Another important formal development in rock music has been the so-called concept album, a succession of musical pieces tied together by a loose narrative theme. Much rock music is performed at high volume levels, so the music has been closely tied to developments in electronic technology. Rock musicians have pioneered new studio recording techniques, such as multi-tracking—a process of recording different song segments at different times and layering them on top of one another—and digital sampling, the reproduction by a computer of the patterns of a particular sound. Rock concerts, typically huge events involving thousands of audience members, often feature high-tech theatrical stage effects, including synchronized lighting. Rock music is a genre of popular music with a prominent vocal melody, accompanied by electric guitar, bass guitar, and drums. Many styles of rock music also use keyboard instruments such as organ, piano, mellotron, and synthesizers. Other instruments sometimes utilized in rock include saxophone, harmonica, violin, flute, French horn, banjo, melodica, and timpani. Also, less common stringed instruments such as mandolin and sitar are used. Rock music usually has a strong back beat, and often revolves around the guitar, either solid electric, hollow electric, or acoustic.