Johann Sebastian Bach, Woody Guthrie and Led Zeppelin walk into a Mexican restaurant in Chicago. If you know a joke that starts like that, save it for later. This is about a new CD, and there's no punch line. Except that it's dang good.

The fact is you just don't expect to find the sprightly second movement from Bach's third Brandenburg Concerto, Guthrie's expansive 'This Land is Your Land' and the polyrhythmic Zep scorcher 'Four Sticks' all on one album. You really don't expect to find them played by a band that specializes in Mexican traditional music, performed on folk instruments, let alone by a band based in the Windy City. And should something of that sort exist, you would expect it to be meant as a gag. But 'Esta Tierra Es Tuya (This Land Is Your Land),' the new, third album by Sones de México, neatly manages all that, while sidestepping that last bit.

"Some people have called those novelty songs," says Juan Díes, who plays various stringed and percussion instruments and produces the group's recordings. "I don't see them that way. Our CDs are autobiographical. They represent things we encounter. We play traditional Mexican music, Mexican son. That's our core. But we don't pretend to be living in a small village in Mexico when we're in the middle of Chicago."

Let's not overlook that most of the album is traditional Mexican music from various styles and regions, expertly and vibrantly performed. And Díes readily admits that the non-Mexican-sourced songs may well be the draw for many people. "They are points of entry to the rest of the material," he says. "We're very serious about our traditions, but a lot of people wouldn't pick up a Mexican folk record just like that."

And, he notes, a lot of Mexican music that people hear is hardly pure to begin with. "I do feel a mission to educate people, not as a lecturer, not in an academic sense, but to reveal parts of Mexican culture that may not go along with some of the stereotypes or the most known things -- mariachi or technobanda or narcocorridos or things that are flooding the airwaves," says Díes, who was born and raised in the town of San Luis Potosi before moving to Indiana for college when he was 18, in 1982, where he studied ethnomusicology and later took a job at the famed Old Town School of Music in Chicago. "Instead we want to look at the unknown parts of Mexico."

That includes various takes on Mexican son traditions from different regions, looks at the roots of mariachi, an adaptation of the venerable ghostly lament 'La Llarona' (The Weeping Woman) and an original chilena, 'Eres Bella Flor,' by Sones music director Victor Pichardo, played on a total of more than 50 traditional acoustic instruments by the group's five members.

The non-Mexican material, though, came about organically and fits well alongside the other pieces. "Victor was in the car with a friend of ours visiting from Veracruz, and Bach came on and the friend said, 'That sounds just like Son Jarocho!' and a light went on in Victor's head," Díes says. "If you listen to music from Veracruz and Bach side by side you can see there's a lot of skill and worthiness in both of them. We wanted to put Mexican folk music on a pedestal and get more respect for it."

And, of course, as a spate of CDs released in the last decade of so show, there was a strong Baroque presence in Latin America for centuries thanks to the European colonialists.

If doing 'This Land Is Your Land' in Spanish with a Mexican arrangement seems like a political statement, it is. "That started less as a musical idea and more as a concept," he says. Díes knew the song well from his Old Town School days and was aware of Guthrie's active interest in farm labor issues of the Dust Bowl years and beyond. Inspired by an immigration rights march on May 1, 2006, the group took a stab at an adaptation.

"The message of the song is about sharing, welcoming ... to work and have a right to live and be prosperous," he says. "We didn't change a lot of it to convey the message of the Mexican people. All we did was change the rhythm a little and a little in the lyrics and put a norteño or ranchera beat to it."

The Zep track was actually the closest to a joke -- at first. "There's a school of music here in Chicago that was organizing a tribute to Led Zeppelin," says Díes. "Someone mentioned Sones de México thinking, 'Wouldn't that be funny!' We started looking at the repertoire and it wasn't easy. A lot of Led Zeppelin stuff is blues-based, and Mexican music comes from other roots. But we found the rhythms of 'Four Sticks' could be approached either as African or Native American, so we put in some elements of Son Jarocho and some of Aztec ceremonial dance. That was an arrangement of mine."

Novelty or not, the natural attention drawn by those songs does bring Sones to something of a crossroads in regard to future projects. Díes says there is a fine line to walk, though following a planned CD geared toward children with songs the group members grew up with in rural settings, there will be further explorations a la 'Esta Tierra Es Tuya.'

"We may have a jazz song on that one," he says. We have never really done much with jazz, and that's very strong here in Chicago. There was a film made by a Latino director here that never got past the festival circuit, and we did an arrangement of [the jazz standard] 'On Green Dolphin Street' for that, made it into a dance song. And we have some narrative ballads we've never recorded, corridos that tell stories. The thing is I'm trying to make those bilingual. So much of the corrido tradition is based on the lyrics, so someone who doesn't speak Spanish would miss a lot. So I'm trying to make it work in both English and Spanish."

Ultimately, he says, the trick is not to get trapped by labels or expectations of what any kind of music is or isn't supposed to sound like but for the group to find its own effective expressions.

"'World music' is a ridiculous term, and 'pure, unadulterated folk music' is a ridiculous idea," he says. "Once you get into people playing it, everyone has their own voice, incorporates some of themselves into whatever they do. We just happened to be in Chicago instead of Michoacan."

Bach would be amused. And impressed.