Rock and roll is usually explained as rhythm-and-blues music—that is, music performed by black artists for black listeners – repurposed by mostly white artists for a mostly white audience. How do we know this? Because that’s the way the industry trade magazine Billboard represented it.
Billboard started charting songs in 1940. By 1949, it was publishing charts in three categories: pop, country-and-Western, and (a new term, replacing “race music”) rhythm and blues. Every week, in each category, there were lists of the songs most frequently sold in record shops, most frequently requested in jukeboxes, and most frequently played by disk jockeys. (These rankings were all relative; actual sales figures were proprietary.)
The charting system was predicated on a segregated market. How did Billboard know when a song was a rhythm-and-blues hit, and not a pop hit? Because its sales were reported by stores that catered to an African-American clientele, its on-air plays were reported by radio stations that programmed for African-American listeners, and its jukebox requests were made in venues with African-American customers. Black artists could have pop hits. The Ink Spots, a black quartet, had fourteen songs in the Top Five on the pop chart between 1939 and 1947. That was because their songs were marketed to whites.
Louis Menand, “The Elvic Oracle”, The New Yorker (16 November 2015), 82-83.