Black Sabbath is credited with creating heavy metal. The success of their first two albums - Black Sabbath and Paranoid - marked a paradigm shift in the world of rock. Not until Black Sabbath upended the music scene did the term "heavy metal" enter the popular vocabulary to describe the denser, more thunderous offshoot of rock over which they presided. With their riff-based songs, extreme volume, and dark, demonic subject matter, Black Sabbath embodied key aspects of the heavy-metal aesthetic. Yet in their own words, they saw themselves as a "heavy underground" band. That term denoted both the intensity of their music and the network of fans who found them long before critics and the music industry took notice.

The demanding pace of the road and various lifestyle excesses began catching up with Black Sabbath by the mid-70s following the release of five consecutive genre-defining albums (Black Sabbath, Paranoid, Master of Reality, Vol. 4, Sabbath Bloody Sabbath). Their next three albums - Sabotage (1975), Technical Ecstasy (1976) and Never Say Die! (1978) - all had memorable moments but lacked the unalloyed brilliance of their predecessors.

The band's second to last album to feature frontman Ozzy Osbourne, 1976's Technical Ecstasy finds the forefathers of heavy metal experimenting with their signature sound by implementing more keyboards, synthesizers and orchestrations. The 8-song set is highlighted by the tracks "Back Street Kids," "All Moving Parts (Stand Still)," "Dirty Women" and even includes a rare lead vocal from drummer Bill Ward on "It's All Right."