source states that "Louis Jordan joined Turner in laying the foundation for R&B in the 1940s, cutting one swinging rhythm & blues masterpiece after another". Other artists who were "cornerstones of R&B and its transformation into rock & roll" include Etta James, Fats Domino, Roy Brown, Little Richard and Ruth Brown. The "doo wop" groups were also noteworthy, including The Orioles, The Ravens and The Dominoes. The term "rock and roll" had a strong sexual connotation in jump blues and R&B, but when DJ Alan Freed referred to rock and roll on mainstream radio in the mid-1950s, "the sexual component had been dialed down enough that it simply became an acceptable term for dancing". History Precursors The great migration of Black Americans to the urban industrial centers of Chicago, Detroit, New York City, Los Angeles and elsewhere in the 1920s and 1930s created a new market for jazz, blues, and related genres of music. These genres of music were often performed by full-time musicians, either working alone or in small groups. The precursors of rhythm and blues came from jazz and blues, which overlapped in the late-1920s and 1930s through the work of musicians such as the Harlem Hamfats, with their 1936 hit "Oh Red", as well as Lonnie Johnson, Leroy Carr, Cab Calloway, Count Basie, and T-Bone Walker. There was also increasing emphasis on the electric guitar as a lead instrument, as well as the piano and saxophone. Late 1940s R&B originated in African-American communities in the 1940s. In 1948, RCA Victor was marketing black music under the name "Blues and Rhythm". In that year, Louis Jordan dominated the top five listings of the R&B charts with three songs, and two of the top five songs were based on the boogie-woogie rhythms that had come to prominence during the 1940s. Jordan's band, the Tympany Five (formed in 1938), consisted of him on saxophone and vocals, along with musicians on trumpet, tenor saxophone, piano, bass and drums. Lawrence Cohn described the music as "grittier than his boogie-era jazz-tinged blues". Robert Palmer described it as "urbane, rocking, jazz-based music ... [with a] heavy, insistent beat". Jordan's music, along with that of Big Joe Turner, Roy Brown, Billy Wright, and Wynonie Harris, is now also referred to as jump blues. Already Paul Gayten, Roy Brown, and others had had hits in the style now referred to as rhythm and blues. In 1948,