In a broad sense, pop is any music based on memorable melodies, repeated sections (usually, but not always, verses and choruses), and a tight, concise structure that keeps the listener's focus on those elements. Pop music has been a profitable industry in America since the 19th century, but for these purposes, pop is a style that took shape in the post-rock & roll era, once the more conservative elements of the record industry had come to terms with the new musical landscape. Pop emerged in the late '50s, as the initial rock & roll craze began to die down, and a lighter, smoother (but still similar) alternative to rock was needed. Mostly a singles medium, pop was influenced by the beat, arrangements, and style of rock & roll (and sometimes doo wop), and it didn't sound bad on the radio next to rock & roll. But pop didn't rock as much as rock & roll. It was about professional craft, both in the songwriting and the studio production, and had little to do with the edge or attitude of rock. As the '60s wore on, pop began to incorporate touches of psychedelia and blue-eyed soul; by the '70s, pop had mellowed substantially, thanks in part to the singer/songwriter movement and Bacharach's brand of smooth adult pop. Some of pop's biggest acts in the '60s included the Beach Boys, the Four Seasons, the Everly Brothers (entering a different phase of their career), the Association, the Rascals, the Righteous Brothers, and (in the U.K.) the Walker Brothers and Petula Clark; other major figures included composer Burt Bacharach, producer Phil Spector, and Brill Building songwriting teams like Barry/Greenwich and Goffin/King. The classic '60s-style strain of pop morphed into AM pop and soft rock by the mid-'70s, but today it dominates good-time oldies radio formats.