As far as the mainstream goes, Dave Grohl is pretty much rock's gatekeeper. One need only to see all of the friends he assembles for his Sound City documentary/album to see that, and it's not even the first time he's put on a star-studded show (lest we forget Probot, Them Crooked Vultures or that time he covered "London Calling" with everyone you ever liked ever). There are musicians that might get more critical acclaim. There are those who have set higher album sale records. There are members of the old guard, like Bruce Springsteen, that have stayed relevant. But Grohl is charged with protecting rock n' roll's history, a role that is both undeniable and unenviable. In the case of the film Sound City, he argues for the magic of analog recording, how it draws better performances from people and can lead to something truly magical.

I just wish the soundtrack lived up to that idea.

Released concurrently, the Sound City DVD and Sound City: Real to Reel CD could easily make someone feel cynical from a distance. Compared to other histories, such as the excellent Perfecting Sound Forever by Greg Milner or This is Your Brain on Music by Daniel J. Levitin, Sound City dips a little too frequently into the sentiment that "it used to be so much better, man." It also raises some interesting questions, like how ProTools can sometimes be used to supplement making art without coddling unworthy artists, but doesn't delve deeply enough into them. Granted, those kinds of issues distract from what Grohl wanted to talk about: Sound City Studios in Van Nuys, Calif. and the staff, building and $75,000 Neve 8028 Console custom board that defined it.

On that front, the documentary is hugely winning. It helps to be a fan of Fleetwood Mac, Tom Petty and, um, Ratt, but the assembled talking heads offer up some interesting anecdotes about what it was like to make records. Grohl doesn't intrude too much, occasionally injecting humor as well as his own experience recording portions of Nirvana's Nevermind. Otherwise, the film's first half or so deals with making records in the '70s and '80s [TOTALLY AWESOME SIDENOTE: Dio's Holy Diver and Pat Benatar's Crimes of Passion were recorded at Sound City! Get stoked!]. While it's his first film, Grohl shows strong interviewing skills, coaxing some great stories out of legends like Petty, Neil Young and fucking Rick Springfield, whose career was essentially made by Sound City.

In 1991, Sound City Studios was booming thanks to Nevermind. Just a decade later, it shuttered its doors after digital recording drove it out of business. Grohl bought the studio's recording console, which he employs in the film for some jam sessions with Butch Vig and celebrity friends. Sound City then essentially becomes an advertisement for itself, although it stumbles. The inclusion of Stevie Nix provides some nice circular storytelling, given that Fleetwood Mac were actually formed at Sound City Studios, but her contribution, "You Can't Fix It," is embarrassing.

The session between Grohl, Josh Homme and Trent Reznor, however, is amazing. It's an alt-rock wet dream for sure, but watching the way they jam out and discuss ideas for what will eventually become the song "Mantra" feels warm, genuine and human. Homme and Reznor also represent divergent ideals. Homme is an analog guy all the way and even made the Queens of the Stone Age record Rated R at Sound City. Reznor doesn't have any retro fetishes, instead observing that digital recording is a tool like any other. It makes it easier for bad bands to make bad records, but it also enables good bands to make good records when employed tastefully. This whole conversation is enticing but brief.

That said, the best moment in the entire film is when Paul McCartney talks about breakdowns. Because he's a got-damn Beatle in a room full of punks. Because he's probably one of the most musically gifted people in the world. Because he's Paul McCartney and he's talking about breakdowns. Also, his tune with a reconstituted Nirvana, "Cut Me Some Slack," is the "Helter Skelter" sequel you didn't know you needed.

The film suggests that music needs to be wrought from A) hard work and B) collaboration. ProTools makes it too easy to fix things, which means that ideas might not get as much review as they would in an analog setup. Foo Fighters and Springfield collaborate on a tune, "The Man That Never Was," and it is only through repetition that they arrive at the riffs they really want. Ease of use is always nice, but it doesn't always breed creativity the way we think it can. The control board is massive and editing is a bitch, but in a way it doesn't get simpler than a couple of guys locked in a room with their guitars.

Sound City isn't the hardest hitting documentary, more a collection of anecdotes about the way music used to be, but it's still an engaging viewing. And it is nearly undone by its mixed bag of a soundtrack. "Mantra," Cut Me Some Slack" and "The Man That Never Was" are highlights, but it's kind of revealing how the worst songs aren't mentioned in the movie at all (Besides that Nix song. Yeesh). The film shows how great music can get using '70s recording techniques; the soundtrack shows how awful '70s rock got before punk came along. Slipknot's Corey Taylor turns in a hammy mid-tempo rocker that's probably the worst track, but plenty of the album's middle is forgettable blues rock.

Real to Reel would have benefited from more diversity. Springfield's clean power pop effort gets seated next to Lee Ving's "Your Wife is Calling." Foo Fighters pretend to be Fear for a song about beer (obviously), and it's a fine blend of humor, Cali punk and blues. These songs have no business next to each other, which makes the dichotomy so great. The rest of the album needs to be this diverse, and it's just not. It starts strong with Black Rebel Motorcycle Gang's "Heaven and All," but it quickly fades. While there are glimpses of genius throughout, the album cheapens the movie by being so inconsistent. Grohl put all this effort into extolling tape's virtues, and then put out a lackluster record anyway.