When Nine Inch Nails and Soundgarden emerged in the 1980s, they were each going in strikingly different directions. Cleveland's Nine Inch Nails combined the awesome force of industrial music with dark metallic leanings, and came off as stirringly new and forward-thinking. Starting a couple years earlier in 1984, Soundgarden rose out of the vibrant chaos of punk and the ensuing cerebral reinventions of postpunk to crank up a sound that was decidedly evocative of heavy metal, launching a revival of more safely comforting rock sounds, which paved the way for grunge. Usually when rock bands end up at the Hollywood Bowl, it means that their critical mass has already peaked and they're on the long, slow side into nostalgia. But NIN's recent tours still have the power to unsettle.