The expansion of FM in the mid-1960s created room for experimenting, particularly with classical music, jazz, blues, and non–Top 40 rock songs. Progressive rock emerged as an alternative to conventional formats. Many noncommercial stations broadcast from college campuses, where student deejays and managers rejected the commercialism associated with Top 40 tunes and began playing lesser-known alternative music and longer album cuts (such as Bob Dylan’s “Desolation Row” and the Doors’ “The End”). Until that time, most rock on radio had been consigned almost exclusively to Top 40 AM formats, with song length averaging about three minutes.

Experimental FM stations, both commercial and noncommercial, offered a cultural space for hard-edged political folk music and for rock music that commented on the Civil Rights movement and protested America’s involvement in the Vietnam War. By the 1970s, however, progressive rock had been copied, tamed, and absorbed by mainstream radio under the format labeled album-oriented rock (AOR). By 1972, AOR-driven album sales accounted for more than 85 percent of the retail record business. By the 1980s, as first-generation rock and rollers aged and became more affluent, AOR stations became less political and played mostly white, post-Beatles music featuring such groups as Pink Floyd, Led Zeppelin, Cream, and Queen. Today, AOR has been subsumed under the more general classic rock format.