The studio version of "Cut Me Some Slack," the song debuted by Paul McCartney and the surviving members of Nirvana last Wednesday night (December 12th) at the 12-12-12 benefit concert in New York, has been released on iTunes. The surprise collaboration was recorded for Nirvana drummer/Foo Fighters frontman Dave Grohl's upcoming documentary Sound City, which will premiere at the Sundance Film Festival in January before rolling out via Blu-ray, DVD and VOD on February 1st.

The raw-sounding track comes across as heavier than what one might expect to hear from McCartney, but Grohl told us a while back that Nirvana liked to rock as hard as any other band: "There was a lot of that crazy, heavy element in Nirvana. You know, the one thing that Nirvana was against was just the bulls**t."

McCartney, Grohl, Nirvana bassist Krist Novoselic and Nirvana/Foo Fighters guitarist Pat Smear premiered the song live during the all-star charity concert, which was organized to raise money for the victims of Hurricane Sandy.

Grohl, Novoselic and Smear have not performed together onstage since the last Nirvana tour in 1994, before the death of band leader Kurt Cobain.

The former Beatle said he had no idea that he was jamming with three-quarters of Nirvana during the recording session, explaining, "I didn't really know who they were. They are saying how good it is to be back together. I said, 'Whoa? You guys haven't played together for all that time?' And somebody whispered to me, 'That's Nirvana. You're Kurt.' I couldn't believe it."

The soundtrack to the documentary, which chronicles the history of a legendary Los Angeles recording studio, will be released on March 12th.

The 11-song soundtrack contains a number of blockbuster collaborations involving Grohl, the other members of Foo Fighters, Stevie Nicks, Trent Reznor, Josh Homme, Rick Springfield, Corey Taylor and more.