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. Soul came to describe a number of R&B-based music styles.
Rock & Roll
Rock & Roll is often used as a generic term, but its sound is rarely predictable. From the outset, when the early rockers merged country and blues, rock has been defined by its energy, rebellion and catchy hooks, but as the genre aged, it began to shed those very characteristics, placing equal emphasis on craftmanship and pushing the boundaries of the music. As a result, everything from Chuck Berry's pounding, three-chord rockers and the sweet harmonies of the Beatles to the jarring, atonal white noise of Sonic Youth has been categorized as "rock." That's accurate -- rock & roll had a specific sound and image for only a handful of years. For most of its life, rock has been fragmented, spinning off new styles and variations every few years, from Brill Building Pop and heavy metal to dance-pop and grunge. And that's only natural for a genre that began its life as a fusion of styles.
Jazz has been called America's classical music, and for good reason. Along with the blues, its forefather, it is one of the first truly indigenous musics to develop in America, yet its unpredictable, risky ventures into improvisation gave it critical cache with scholars that the blues lacked. At the outset, jazz was dance music, performed by swinging big bands. Soon, the dance elements faded into the background and improvisation became the key element of the music. As the genre evolved, the music split into a number of different styles, from the speedy, hard-hitting rhythms of be-bop and the laid-back, mellow harmonies of cool jazz to the jittery, atonal forays of free jazz and the earthy grooves of soul jazz.