During the '70s, FM radio stations gradually diluted the freewheeling innovations of pirate radio and early FM stations. Theoretically, the new stations did what the pioneers did -- play album tracks instead of singles -- but they soon relied on a set group of artists for their playlists. The one thing that tied all these Album Rock artists together was their dedication to the album as the vehicle for their music, plus their reliance on rock as the foundation of their music. That means album rock consisted of everything from heavy metal and Southern blues-rockers to prog-rock and singer/songwriters with supporting rock bands. It was fairly diverse, actually, but they all shared a certain artistic aesthetic and little bit of indulgence, plus their constant exposure on FM radio. These album rock bands ruled the '70s FM airwaves. They persevered into the '80s, but when album rock radio evolved into classic rock radio, fewer and fewer of their new albums hit the airwaves. By the '90s, album rock acts still turned out new albums, but their older material was heard on the radio -- and usually in the reunion concerts these bands mounted.