Thank god this documentary on the venerated SoCal recording studio wasn't made by some douchey rock snob with a boring retro-gear fetish, but instead by lovable Foo Fighter Dave Grohl, who with Nirvana recorded Nevermind there and has been grateful ever since. Grohl is no Luddite, but to him Sound City stood for a very special kind of pre-digital magic. Carrying us through the studio's cycles of near-obsolescence and revitalization by recurrent new waves of analog appreciation, he has great fun sweeping through the historic parade of latter-day rock royalty whose hit records came out of the place. He also burrows cozily into Sound City lore, like the purgatory of countless takes required to bring forth Tom Petty's "Refugee," or the kismet by which young unknowns Lindsay Buckingham and Stevie Nicks happened to catch Mick Fleetwood's ear. Grohl also does a good job of filling out his movie with studio personnel and other supporting characters, not least a custom mixing console that when new cost about twice as much as its owner's house. (Now, we learn, the board lives in Grohl's own Studio 606, whose forthcoming projects include an album full of Sound City all-stars.) This is a warm and winning tribute — entirely forgivable for lingering too long, like a band that keeps playing encores because with a groove this good, who'd want to go home?