Friday at the Folk Fest runs the gamut of contemporary string band music. From mandolinist David Grisman, the man who first gave traditional bluegrassers something to complain about, to young genius cellist/madman Rushad Eggleston to fiddle prodigy Brittany Haas, who matriculates at Princeton days after the festival, the playing will be brilliant.

Smiling from the center of this swirl of strings is Darol Anger, original member of Turtle Island String Quartet, jazz instructor and one of Grisman's original co-conspirators in the New Acoustic Music movement in the 1970s. He's also band leader of the Republic of Strings, which includes Eggleston and Haas, along with guitar legend Scott Nygaard.

Anger checks in by phone from a hotel room overlooking the Grand Tetons, where he's playing a bluegrass festival. Anyone familiar with Anger's body of work, from Turtle Island through the Republic of Strings recording, might be a bit surprised to find the fiddler in the 'grass, given Anger's propensity for Brazilian/African/Stevie-Wonder type tunes. He laughs and says he's there to play with anybody who will let him, like Sam Bush and Drew Emmett. "I came to pick."

His enthusiasm is still intact after some 30 years of music-making. Anger remarks that it was bluegrass, after all, that saved his years of classical violin training from abandonment. "Bluegrass is one of the great rhythmic inventions of any age." He recalls seeing bluegrass fiddler Richard Greene with folk-rockers Seatrain.

"For a 13-year-old boy, it just turned me around, got me into violin again." Anger went on to learn countless tunes from Byron Berline, and names another monumental influence: "Vassar Clements showed me that you could go deep, plumb the depths of human frailty. He showed me that fiddle tunes went beyond dance music."

(Sadly, Clements died on Aug. 16, within two days of this conversation. The next day, Anger's home page was revised to include a written tribute and a picture of the two jamming. It's a safe bet that Anger will not be the only one at the festival dedicating tunes to the memory of the greatest practitioner of hillbilly jazz we ever knew.)

"The last few years the joy has been the intergenerational connection, the passing on of string band music," says Anger. "This is one of the few art genres where there is a respect from the younger to the elder." He kvells at the accomplishments of young players like Eggleston, who bows the fanciest Appalachian fiddle tunes on cello with such delicate strength it seems almost too good to be true. Hear him also with his contemporary/old-time band, Crooked Still, in a separate set on Friday afternoon.

Whereas Eggleston is old enough to have finished Berklee, Haas is just out of high school. Her former teacher passed her along to Anger, who laughs, "She learned everything I know in about six weeks." He notes that Republic of Strings will carry on when she leaves for Princeton, but it surely will not be the same without her.

The dance tent gets my endorsement as best innovation yet at the festival. A huge wooden dance floor covered by a tent, to mute the effects of the elements, awaits long sets from the festival's featured bands, giving pleasure to both dancers and listeners alike. Learn to swing dance to jaw-dropping live licks from the Red Stick Ramblers. Learn to clog with the legendary Footworks ensemble. Welsh, Mexican, Cape Breton and a host of other styles will be taught throughout the weekend.

Peggy Seeger, a passionate supporter of traditional song, is also an inspired gadfly, long known for her well-written social commentaries like "Four Minute Warning" and "Gonna Be an Engineer."

Quetzal plays the full spectrum of Mexican-American music, from very traditional to originals in the contemporary vein, with an emphasis on dance rhythms.

The Campbell Brothers bring sacred steel guitar back to its home (legend has it the style was invented in Northwest Philly). Their energetic gospel sets get everyone up and shouting, regardless of religious convictions.

Arlo Guthrie is celebrating 40 years of embroidering upon the tale of Alice's Restaurant. With any luck he'll treat us to the Philly-centric "Rainbow Roach Affair" when he wraps up the festival on Sunday night.

The Philadelphia Folk Festival runs Aug. 26-28, Schwenksville, Pa. See www.folkfest.org for a complete schedule.