Mark Ronson had worked with Paul McCartney before, but only as a DJ at the former Beatles legend's 2011 wedding to Nancy Shevell. Their relationship actually goes back to when Ronson was a boy, and McCartney even saved his life once. Still, there was initial trepidation from Ronson when McCartney tapped him to produce three songs for an as-yet unnamed project.

"He understands that you're so nervous to be working with Paul McCartney -- 'cause everyone is," Ronson tells Billboard. "He gives you a lot of leeway, but then at the end of the day you need to deliver the goods."

Ronson is best known as the Grammy-winning producer of Amy Winehouse's 'Back in Black.' He's also helmed projects with Kaiser Chiefs, Duran Duran and, most recently, Rufus Wainwright. He is also the stepson of Mick Jones of Foreigner, which is how they two knew each other so many years ago.

McCartney, meanwhile, is completing his initial release since digging back into songbook and jazz songs from his father's era on an album called 'Kisses on the Bottom.' Though McCartney has been active in reissuing some of his classic 1970s solo sides, he hasn't actually produced a new album of pop music under his own name since 'Memory Almost Full,' back in 2007. The collaborative Fireman project followed in 2008.

No surprise, then, that the pressure was on for Ronson.

"He's done every kind of music. He invented the rule book in several different ways," Ronson adds. "I don't know if (our stuff) is revolutionary, but they're brilliant songs. I just tried to give him a sound he was looking for."