Deep Purple released four albums in the early '70s that helped define heavy metal 1.0: In Rock, Machine Head, Burn and Fireball. This record has aged really well; crank it for some whippersnapper, and he'll assume it's the latest in stoner-rock cool. In addition to killer performances from guitarist Ritchie Blackmore and howler Ian Gillan, Fireball boasts fantastic production. It's brutal, yet it's also slyly refined. Every sound, possessing texture and depth, is well placed. When old heads wax philosophic about how good rock sounded "back in the day," this is what they're talking about.