Though the current wave of synth-pop imagines a high-gloss, fantasy future, an equally vibrant trend has seen countless artists - from Jack White to Mumford & Sons - reaching back to folk, country and the blues.

Carolina Chocolate Drops very much belong to the latter crusade.

They come from North Carolina, whose Appalachian Mountains have long been the home of bluegrass music, previously thought to be an exclusively white, hillbilly tradition.

As the band's name also implies, however, the four members of this intriguing group are black.

Their mission, initially at least, was to salvage a little-known string-band tradition among Depression-era African-Americans before it passed out of living memory. The original trio, Rhiannon Giddens, Dom Flemons and Justin Robinson, first met at the Black Banjo Gathering, a 500-strong meeting of like minds, which took place in the state in 2005.

"In the mainstream old-time banjo community," says Giddens, a vocally-gifted opera graduate of Oberlin Conservatory, "there was much hostility to the idea of the banjo being an African-derived instrument but it actually originates from slave communities there."

"In America," adds Flemons, "we tend to focus on the white guys that sound black, not vice versa."

Immediately after the gathering, Giddens, from nearby Greensboro, and Flemons, who came from Arizona, formed a group called Sankofa Strings, which, according to Flemons, "was focused around jazz, blues and the broader aspects of string-band music."

A few months later, Flemons moved to North Carolina and they formed Carolina Chocolate Drops, he says, "to focus specifically on the string-band music of the Piedmont region" - an area to the east of the Appalachian foothills.

There, Robinson had made contact with a veteran fiddle player called Joe Thompson, who is its last-known purveyor from the 30s and 40s.

While Thompson, pushing 90, recovered from a stroke, the trio began visiting his home in Mebane to learn all the old songs and jigs he could remember.

Thanks to that romantic back story, and their spirited re-imagining of this arcane style, the band's popularity quickly spread beyond the local area, building on a handful of well-received indie album releases, with 2010's Grammy-winning major-label debut, Genuine Negro Jig.

In Carolina Chocolate Drops' banjo-pickin' hoedowns, there is, of course, something hugely consoling for those listeners disenchanted with contemporary pop's auto-tuned singing and smoke-and-mirrors production. On top of their energetic preservation of a fading cultural heritage, there's perhaps a welcome message, too, in their pedagogic relationship with Thompson - the internet can't teach you everything.

Carolina Chocolate Drops, however, are not stuck in the '30s.

Flemons points out that the Black Banjo Gathering developed out of a Yahoo chat room.

While erudite and learned in their field, the band present anything but a static history lesson through their music.

Says Flemons: "Our first impression was that we were hell-bent on string-band music, but we've always tried to be expansive and connect different dots as we go along.

"For instance, Riro's House [the opening track from their latest album, Leaving Eden] was a fiddle-and-banjo tune we learnt from Joe, but I saw a way that I could incorporate a fife-and-drum beat into it, just taking ideas I'd heard in some Alan Lomax recordings."

So, while their chosen instruments may seem arcane - they deploy banjo, fiddle, mandolin and bass drum, as well as curiosities like kazoo, jug and "bones" (two animal bones rattled percussively like castanets) - they are out to conduct folkloric unfinished business, to create fusions that have never happened.

"And ultimately," Giddens concludes, "we just have to play what feels good. It almost doesn't matter what instruments you play - it's how you play them."

Last month, the new four-piece line-up - Giddens and Flemons, now augmented by Hubby Jenkins (multi-instrumentalist) and Leyla McCalla (cellist), who are all aged between 26 and 35 - gave a rousing performance at London's rarefied folk mecca, Cecil Sharp House.

Musically, they were a purist's nightmare. Giddens sang songs in various idioms, including Gaelic puirt à beul, Bessie Smith-style theatrical blues and contemporary R&B (their sassy take on Blu Cantrell's Hit 'Em Up style).

McCalla, meanwhile, delivered a lament from her native Haiti, and plucked basslines on her cello which hinted at New Orleans funk. Still, they brought the house down.

Leaving Eden sticks a little closer to the string-band script but its producer, Buddy Miller, favoured a fittingly speculative approach.

"He just allowed us to work on creating a sound that we hadn't even found yet," says Jenkins, "with the chirping of crickets coming in through the windows."

Homespun yet exploratory, Carolina Chocolate Drops really are a breath of fresh air.

• Leaving Eden is out at the end of the month