From barbershop quartets to U2's Bono, human voices are uniquely expressive. A powerful singer can convey greater nuance and emotion than nearly any instrument in the world -- something composers have known for ages. When you put two-dozen of these pipes together, black dots on paper leap to life. Still, writing for choir isn't something most folks get to do every day. But 25 Green Mountain tunesmiths recently got the chance, commissioned by Vermont's very own community chorus, the aptly named Social Band.

The 24-member a cappella group's usual repertoire ranges from American shape-note and Appalachian styles to music from the European Renaissance. Founded in 1998 by Liz Thompson and Don Jamison, the chorus has been under the artistic direction of Amity Baker since 2001. Their 2003 CD, Florona, featured early music from around the world. This time, they're sticking closer to home.

Social Band will perform works from the Vermont Composers Project at three concerts next month, in Montpelier, Vergennes and Burlington. Although they're mostly known for singing "well-aged" works, not everything the singers perform is from another century. "We've always sung original stuff, and part of our founding mission was to encourage the composition of new choral works," Baker says. "At one point we figured that about 20 or 30 percent of our material was new, and a lot of it was written by members of the chorus. So then we started talking about performing all original songs by all Vermont composers."

Social Band is a mix of male and female, some younger, some older; many members are native Vermonters, others recent transplants. Friendship and a love of vocalizing is the common ground.

At a recent rehearsal at Christ Church on the University of Vermont's Redstone Campus, Baker conducts her group with contagious enthusiasm, occasionally singing along in order to reinforce inflections and solidify harmonies. Animated and feisty, she uses her sharp sense of humor to get the most from the chorus. "Let's try that one more time, and see if you can spare some brain cells to make it lock in," she says during a short break. The ribbing works -- when they begin again, the singing is fluid and dynamic, a powerhouse of polyphony.

It's no wonder Social Band are working so hard -- they've got a wide range of material to cover. Among the contributors to the Vermont Composers Project are singer-songwriters Patti Casey and the late Rachel Bissex, quirky non-pop symphonist David Gunn, Burlington folkie Robert Resnik and Troy Peters, conductor of Vermont Youth Orchestra and Middle- bury College Orchestra. It's an eclectic crew -- and so are their compositions. Gunn's piece is about a slug, "an animal all too infrequently sung about in these otherwise enlightened times," according to the composer. Casey's contribution is a reflection of her "Buddhist leanings and deep love for bluegrass."

The Composers Project is an ambitious undertaking, but Baker feels Social Band are up to the task. "All of the singers take making music seriously and are willing to spend their precious time to do that," she vows.

That doesn't mean they can't have a little fun, and Baker knows how to make it happen. Christ Church is as comfortable as most people's living rooms, with large potted plants and a brick fireplace. But the chorus is sounding a bit stiff. "We need some hips here," Baker implores, halting them mid-song. "Don't be afraid to experiment with your body." And they do, shaking their stuff in exaggerated fashion. Although they might have to tone down the boogie before their upcoming performances, Baker's advice serves a practical purpose -- the group has managed to capture that elusive "swing."

New Haven composer Moira Smiley's piece, "Find Ways," is dense and complex, featuring cascading and somewhat atonal lines. But Baker hears everything, right down to the singers' respiration. "These guys need time to breathe," she says, singling out the male tenors. A few moments are spent closely examining some of the more difficult harmonies. "Let's have another crack at it," Baker says. "A crack addict?" a chorus member responds. With all the joking, it sounds a lot like a rock band practice.

The singers flip through black binders filled with the tunes they'll be rehearsing, making little notes here and there. The process is painstaking but ultimately rewarding, judging from the looks on their faces when they get it right. "Hey, it's coming together," Baker says encouragingly after getting through R.W. Keller's socialist-leaning, agriculturally themed "A Digger's Song." "It could sound a lot worse -- we've heard it!" There's no time to gloat, however. She immediately gets them started on another tune, snapping her fingers to count it off.

Baker hasn't had a lot of formal musical training. "I started singing in the car on long trips with my mother and my sister," she says. "That's where I learned to hold my own part." She also gained experience from singing hymns and anthems every week at church. Now 32, Baker teaches all around Vermont, holding choral workshops and directing summer music camps for children.

Other Social Band members come from backgrounds as varied as the composers contributing to the project. Although church and school chorus were typical starting points for many of the singers, band member Marcia Brewster claims to have begun vocalizing "in the womb." Susan Miller Coulter never sang in public until moving to Vermont at age 51. Former New Yorker Ken Brown split for the Green Mountains in the '70s, trying out the hippie lifestyle. This is his first professional gig. Stephanie Kaza comes from a very musical family. "Both of my parents went to Oberlin Conservatory," she explains. "My father taught high school band in Portland, Oregon, and played in the symphony. My mother gave piano lessons at home, on our Steinway grand."

Their backgrounds may be different, but these singers appreciate the "social" aspect of the band. "I love the harmonies when we're working on a song together, and the laughter in between," says Ginger Gellman. "It's an animated and witty group." Co-founder Jamison enjoys "the individuals in all their quirkiness, and the joint effort to create beautiful sounds." C.C. McKegney explains it this way: "There are no prima donnas. We are supportive of one another. We're learning to sing together better and better, and that's immensely rewarding."

The composers see the project as an opportunity to try out new styles, and to have a little fun in the process. "I wanted to write a good piece of music which would challenge them and tickle their funny bone at the same time," says Irasburg's Sara Doncaster of her composition "The Quangle Wangle's Hat." Based on Edward Lear's nonsense poem, the tune is a whimsical romp crackling with youthful energy.

Doncaster is director and co-founder of the Warebrook Contemporary Music Festival, and has written extensively for voice. She says the Vermont Composers Project is ambitious. "But I think that by striving higher and further than usual, it'll have lasting benefits for the community and the composers."

Brattleboro's Peter Amidon has arranged for chorus before, but "Beatitudes" is his first composition for a vocal ensemble. "It's from the Bible," he explains. "Blessed are the poor, blessed are the peacemakers, and so on. I like what they've done with it very much."

The self-taught Betsy Brigham of Marshfield began writing for chorus as a member of central Vermont's medieval-themed Anima, where she first met Amity Baker. Brigham has never composed for a group that she wasn't directing herself. "I wasn't able to try it out along the way," she says. "Typically when I get about 90 percent finished, I'll take it and rehearse it. And then change it," she says with a laugh.

Brigham finds the Vermont Composers Project a worthwhile undertaking. "I'm glad that Social Band has the energy and enthusiasm to take it on," she says. "The friends I have in the group say that it's really stretching them in a good way -- they're singing stuff that they would never have chosen otherwise."