Patrick Stump's hip-hop crossover -- The Fall Out Boy singer works with Lupe Fiasco, and the Roots

Joining the ranks of John Mayer, Adam Levine, and Chris Martin, Fall Out Boy singer Patrick Stump has crossed over to become hip-hop’s go-to rock dude. He produced last year’s ”Little Weapon” for Lupe Fiasco, a pal from their formative days in Chicago’s music scene, and more recently sang the hook for the Roots’ ”Birthday Girl,” the likely first single from their CD Rising Down (out April 29).

”I’ve always made beats for myself, just for s—s and giggles,” Stump says, adding that he was ”totally surprised” when Fiasco asked to rap over one of his creations. ”I had assumed it was just me kidding myself with a laptop.” The Roots’ Ahmir ”?uestlove” Thompson, who’s jammed with Stump at pre-Grammy bashes for the past three years, says he was won over by the self-described record nerd’s obscure music knowledge: ”He and I go toe-to-toe for hours trying to out-iPod each other. Everything I think I’m up on, he outdoes me. He’s like Jack Black in High Fidelity!”

Next up, Stump is producing several rap-centric cuts for Gym Class Heroes’ fourth CD, due this summer. ”I don’t think a lot of people realize that [Gym Class Heroes frontman Travis McCoy] is an emcee — that’s really his first love. And I don’t think he got to shine on that last record.” Despite his confidence, the emo crooner’s also quick to keep his newfound skills in perspective. ”I don’t think I could ever convincingly have been any type of hip-hop star,” Stump laughs. ”But I’m definitely a hip-hop fan.”