The Billboard Cover Story - Jagger's James Brown: 'Get On Up''s Musical Boot Camp

Keith Jenkins spent 12 years playing guitar in James Brown's final band, The Soul Generals. He was enlisted for Get On Up to give the 80 or so musicians cast as members of Brown's legendary bands, The Famous Flames and The JBs, a taste of life working for the Godfather of Soul.

"We wanted them to feel like a real band," says Margaret Yen, Get On Up's music supervisor. "The James Brown band, whatever incarnation it was, rehearsed and played all the time. I wanted the same kind of bonding and camaraderie, and I wanted it reflected on camera."

It worked. The musicians, who appear in 13 different configurations throughout the film, hung out after shooting and played music at bars around Natchez and Jackson, Miss. Many were college students at Alcorn State and Jackson State, a few were local musicians, and some drove the three hours from New Orleans. They rehearsed in the basement theater of an unheated, shuttered middle school in Natchez.

More than two dozen on-camera performances form the film's musical spine, giving audiences an overview of Brown's innovations and the motivation behind his music as it evolved. Pro­ducer Brian Grazer likens the music team's efforts to a lesson he learned filming the 2002 Eminem movie 8 Mile.

"Ultimately, Dr. Dre said, 'Man, just don't clown out our world.' I got it. That just meant, 'Be authentic,' " says Grazer. "That's something a producer can control. I can't control the scenes because I'm not the director, but I can have a high level of influence on a movie's authenticity."