Within the traditions of American bluegrass and folk, not enough is known of the rich heritage of black string band music.

Those 19th- and 20th-century black fiddle and banjo bands filled their spirited dance numbers, haunting slow waltzes, and gospel laments with clattering spoons and foot-stomping percussion. Their lyrics dealt with God, work, and passion - sometimes all at once in traditional songs such as "Cornbread and Butterbeans."

In the 21st century, the Carolina Chocolate Drops are bent on keeping that rural, rustic music authentically alive - by any means necessary, from the sights and sounds of that trio's sold-out show at Sellersville Theatre on Thursday.

Three African American multi-instrumentalists and singers who met at the Black Banjo Gathering in Boone, N.C., in 2005 formed the Carolina Chocolate Drops in tribute to old-time sound, with education as part of their goal.

During their set, derby-wearing trio member Dom Flemons told the most in-depth stories of who wrote these often uncredited "traditional" songs and how they came into existence. When he wasn't talking or joining in three-part harmonies to songs such as "Salty Dog," Flemons could be found throat singing, banjo plucking, or hooting into jugs that provided a massive bass sound.

If you closed your eyes during the sweetly swaggering rag "Your Baby Ain't Sweet Like Mine" or "Peace Behind the Bridge" - both from the group's most recent CD, Genuine Negro Jig - you could almost hear the hissing of old 78s.

For all the Drops' authenticity, they never seemed to be creating facsimiles. Blame the fact that Rhiannon Giddens and Justin Robinson both come from classically trained families, with Giddens having studied opera at Oberlin Conservatory.

Each served the cause well. Giddens laughed about adding a "little Charleston" to the arrangements' already speedy shuffle when she wasn't busy lending her high, powerful vocals to a manic version of "Jackson." Robinson was quietly stoic as he graced each song with a full-blooded violin sound and occasional lilting vocal.

For all its near novelty-tune status, the trio's version of Blu Cantrell's "Hit 'em Up Style (Oops!)" showed how versatile the trio could be, from Giddens' sauntering vocals to Robinson's beat-box groove. The Drops proved the connection between new jack swing and old-time string band sounds and made each as vital as the other.