Evolving out of jump blues in the late '40s, R&B laid the groundwork for rock & roll. R&B kept the tempo and the drive of jump blues, but its instrumentation was sparer and the emphasis was on the song, not improvisation. It was blues chord changes played with an insistent backbeat. During the '50s, R&B was dominated by vocalists like Ray Charles and Ruth Brown, as well as vocal groups like the Drifters and the Coasters. Eventually, R&B metamorphosed into soul, which was funkier and looser than the pile-driving rhythms of R&B.