Mainstream music fans tend to prefer their live music to sound like it does on the radio. But when the songs have little to no FM presence, it's somehow easier in the minds of listeners to follow the music as it evolves beyond the studio.

		Sonny Landreth Where: Rex Theatre, South Side. When: 8 p.m. Sat. Tickets: $18-$20; 412-323-1919

That's what happens to the songs of chronic road warriors like Sonny Landreth. A world-class slide guitarist nominated for a blues Grammy in 2003, he's one of those guys whose techniques are meticulously detailed in musicians' magazines. And certainly, Landreth is in demand, having put the groove into the sound of heavyweight songwriters like John Hiatt, Mark Knopfler, Dolly Parton, Kenny Loggins and Marshall Crenshaw.

But after decades of doing what he does on the road, Landreth turned to Sugar Hill Records to capture that energy in his first live album. While he's happy with the result, an 11-song gem called "Grant Street," Landreth is quick to pose the obvious philosophical conundrum.

"In the studio the songs are born, and on the road the songs evolve," he ruminates. "So, when you're out on the road touring a live album, where can the songs evolve to? I mean, what do you do when the live album is the one you're supporting?"

You can almost hear the wheels turning through the dead air on the telephone line as Landreth ponders the thought.

"My best answer," he says, finally, "is that I hope these songs stand the test of time."

The 50-year-old Louisiana guitarist has an artistic advantage over many of his more popular musical colleagues. Landreth's audience is more willing to appreciate it whenever the music grows. That's what many will be paying to see when he brings "Grant Street" to Carson Street at Saturday's Rex Theatre concert.

"I've worked with bands that play the same thing every night in the same way," he says. "It really does get into a rut quickly. I mean, it's boring. When creativity goes out the window, I want to follow it. [My music] does fly below the range of radar, but that's indicative of roots music in general. I want to see how the music evolves when it lives in this touring environment."

Recorded on two April nights at the Grant Street Dancehall in Lafayette, La., the new CD is a boiling pot of musical jambalaya, mixing the Creole, Cajun, zydeco and Delta blues of his youth with the smoky jazz and melodic pop sensibilities that have marked much of his later career. Three of the tunes have never been recorded. Performing with longtime sidemen David Ranson on bass and Kenneth Blevins on drums, Landreth intentionally recorded in the spring of 2004 before, he says, "the songs had too long to grow."

"One time, we had been out 200 dates before we took the songs in to record them, and by then I was fried," he recalls. "For this live album, I wanted to make sure we recorded early in the year when the songs were still growing to get the right energy."

"Grant Street" hit the blues shelves this week. The band is rested and the album is new, but Landreth is still thinking about the Darwinian evolution of music.

"You want to be performing the songs before they get too familiar," he says, "but that point was when we recorded them last year. So, now we're picking them up as the album comes out and seeing where the songs will go. That's an interesting thought. This is something new."