It’s been 20 years since the release of Nirvana’s “Nevermind.” The album, which included cultural anthems like “Smells Like Teen Spirit” and “Come As You Are,” marked the beginning of the alt-rock movement of the 1990s and transformed drummer Dave Grohl, bassist Krist Novoselic and singer-guitarist Kurt Cobain into the poster boys of Generation X, until Cobain’s tragic suicide in 1994. Grohl and Novoselic, while slumped on a couch near the same soundboard that they used to record “Nevermind,” reminisced with producer Butch Vig about how they made the album that forever changed their lives and what impact it had on the world.