Any music intended to be received and appreciated by ordinary people in a literate, technologically advanced society dominated by urban culture. Unlike traditional folk music, popular music is written by known individuals, usually professionals, and does not evolve through the process of oral transmission. Historically, popular music was any non-folk form that acquired mass popularityfrom the songs of the medieval minstrels and troubadours to those elements of fine art music originally intended for a small, elite audience but that became widely popular. After the Industrial Revolution, true folk music began to disappear, and the popular music of the Victorian era and the early 20th century was that of the music hall and vaudeville, with its upper reaches dominated by waltz music and operettas. In the U.S., minstrel shows performed the compositions of songwriters such as Stephen Foster. In the 1890s Tin Pan Alley emerged as the first popular song-publishing industry, and over the next half century its lyricism was combined with European operetta in a new kind of play known as the musical. Beginning with ragtime in the 1890s, African Americans had begun combining complex African rhythms with European harmonic structures, a synthesis that would eventually create jazz. The music audience greatly expanded, partly because of technology. By 1930, phonograph records had replaced sheet music as the chief source of music in the home. The microphone enabled more intimate vocal techniques to be commercially adapted. The ability of radio broadcasting to reach rural communities aided the dissemination of new styles, notably country music. U.S. popular music achieved international dominance in the decades after World War II. By the 1950s, the migration of African Americans to cities in the North had resulted in the cross-fertilization of elements of blues with the uptempo rhythms of jazz to create rhythm and blues. Rock and roll, with figures such as Elvis Presley, soon developed as an amalgam of rhythm and blues with country music and other influences (see rock music). In the 1960s, British rock groups, including the Beatles, became internationally influential. Rock quickly attracted the allegiance of Western teenagers, who replaced young adults as the chief audience for popular music. From the late 1960s black pop (see Motown) achieved greater sophistication and a wide audience. The history of pop through the 1990s was basically that of rock and its variants, including disco, heavy metal, punk rock, and rap, which spread throughout the world and became the standard musical idiom for young people in many countries.