A funny thing happened to hip-hop between new albums from the Roots.

Real instruments began creeping back onto urban radio. A raw, thoughtful brand of music, dubbed neo-soul, started getting attention from mainstream audiences. Outkast even won a pair of Grammys.

And the members of the Roots, who for a decade had quietly led the live hip-hop revolution, looked on and gathered a sense of their place in the world and their sense of responsibility to the movement they’d helped foment.

“The expectation was so high,” says drummer Ahmir (?uestlove) Thompson, “there was no way we could come back with just anything.”

“Things Fall Apart,” released to wide acclaim in 1999, had been regarded by many as organic hip-hop’s definitive document: an old-school rap ethic, blended with a socially conscious mindset, steeped and set in a mix of hot soul jamming.

But three years is a long time in the hip-hop world. Long enough to make the Philadelphia band _ ?uestlove, DJ Scratch, MC Black Thought, bassist Hub, keyboardist Kamal and human beat box Rahzel wonder if it was still relevant. (Vocalist Malik B is now estranged from the group.)

“People’s attention spans are real short,” says ?uestlove. “You have to drop a 100-ton anvil on top of their heads.”

For the Roots, “Phrenology” was that piece of heavy metal, albeit with a shot of Philly funk. Released in late November, the album debuted in the top 10 and caught the attention of critics hungry for high-quality releases as the year wound down.

It’s an unconventional triumph of sound and smarts, the most eclectic collection of songs the band has put to tape a gumbo of simmering R’B grooves, hotshot rock ‘n’ roll and complex psychedelic meanderings.

“Daring” is the adjective that often gets propped up next to the Roots’ name. But the way ?uestlove sees it, his band never considered “Phrenology” a risk.

“With us, the live show presentation and the recorded presentation have always been different animals,” he says. “There have been some nights in which, if the right audience was in attendance, we’d do all jazz versions of our songs, or all hard rock versions. If anything, we thought it was time we transferred some of the energy of our live show to wax.”

Fans are accustomed to being startled. ?uestlove recalls the Roots’ 1995 debut release for Geffen Records its first big step out of the hometown scene.

“When Philadelphians got their hands on that, they reacted the same way most people feel about `Phrenology’ now: `What’s this? You’re supposed to be jazzy!'” he says. “We shift gears with every record. I want people to understand we’re not going to do what they expect us to do. We’re sort of a potluck dinner.”

That’s not to say the music on “Phrenology” now on display on a nationwide tour that rolls into the State Theatre tonight was put together on a whim. ?uestlove says it was, in fact, the most carefully calculated Roots album yet.

“This is pretty much the first album where we had a plan that we executed from A to Z,” he says.

While the Roots garner ample respect from their musical peers Talib Kweli, Jill Scott, Common and other hip-hop progressives the band hasn’t been immune from criticism. For all the cultural headway made by the group’s brand of resourceful hip-hop, this remains an era when Nelly can sell 4 million records. Though he won’t point fingers, ?uestlove describes the contemporary record industry as a “state of emergency.”

And he says the urge for the quick, commercial hit hasn’t always been easy to resist.

“I’m not saying we’ve never been tempted to throw it all away and go for the brass ring,” he says. “I could release a platinum record on all the songs I didn’t end up recording. We’ve recorded 300 or 400 songs you just happen to get the pick of the litter when the album comes out. So I don’t want to say we’re above it. It’s just that at the end of the day, we come to our senses.”

?uestlove figures he’ll take 10 years of endurance over 10 million in sales.

“It’s like when squirrels gather their nuts and whatnot, preparing for hibernation,” he says. “That’s what we’re doing. Establishing a really good fan base and a good live show and a good, quality reputation. Those things are what’s important.”