Dave Grohl is impressed by how Sir Paul McCartney is "willing to go off" during jam sessions.
Dave and Krist Novoselic, the two surviving members of Nirvana, teamed up with Paul for a performance at the recent 12-12-12 concert in December at Madison Square Garden, which benefitted those affected by Hurricane Sandy.
Dave and Paul have developed a tight musical bond of late and often play together.
The Foo Fighters rocker understands why the Beatles songwriter is such a legend.
"I remember rehearsing with him for the Grammys. He comes in and just wants to jam," Dave told People magazine.
"He's willing to go off more than most younger musicians."
Dave debuted his new documentary Sound City, about a legendary Los Angeles music studio, at the Sundance Film Festival recently.
New to the film industry, the musician is amazed by how the feature came together.
"The idea was to make a YouTube clip to piggyback on the 20th anniversary of Nirvana's Nevermind [which was recorded at Sound City]," Dave explained.
"We asked a list of people who made records there to be involved: Tom Petty, Neil Young. Everybody got back saying they wanted to be in it.
"I don't know how this movie world works. I'm pretty sure the fact that we completed it is nothing short of a miracle."
Sound City is scheduled for release later this year.