OK, I’ll just say it: The Carolina Chocolate Drops are one of the freshest and most appealing young root-music acts that I’ve seen in my 20-plus years as a music journalist / critic. The Drops play a rustic, organic form of African-American-string-band music that sometimes has a wonderfully / willfully-primitive quality — a style that dates back to the days before the Civil War and remained popular until the mid-20th century.

What makes the Drops unique today is that, for the last 70 years or so, Southern-string- band music has mostly been regarded as the domain of white players from the Appalachian region. However, musicologists and many African-American roots-music players know that not only was there a long, thriving string-band tradition among black musicians — but that many string-band groups were also in the Carolinas, not just in Appalachia.

The Drops home in more specifically on the black-string-band style from the Piedmont region of the Carolinas, where the banjo was typically the lead melody instrument, with the fiddle following along. And then there’s the group’s unique style of percussion, which is achieved by blowing rhythmically into a jug, playing bones, and the “human beat box” sound that Justin Robinson produces with his voice.

The other members of the group are Dom Flemons and the charismatic Rhiannon Giddens, who was trained as an opera singer at the Oberlin Conservatory, and who has been known to leap to her feat onstage and perform a Charleston-dance-routine. Each member is multi-talented — all three sing, all three play banjo and fiddle, and they regularly trade off instruments, which in their case also includes the acoustic guitar, kazoo, autoharp and bass drum.

The Drops, who come to the Michigan Theater on Friday for a show sponsored by the University Musical Society, are no stranger to the Ann Arbor roots-music scene. They tore it up at the Ann Arbor Folk Festival in January 2009, and played the Ark about 14 months ago.

However, their star has been on the rise since the February release of their “Genuine Negro Jig” album — their first for the prestigious Nonesuch label, which has a lot more marketing muscle than the smaller indie labels that released their previous albums, including their revelatory debut, ”Dona Got a Ramblin’ Mind.”

Plus, the latest disc was produced by the popular and influential Joe Henry, who is so ubiquitous that we suspect he might be cloning himself — in the last few years, he’s produced albums for Bettye LaVette, Solomon Burke, Aimee Mann, Susan Tedeschi, Elvis Costello, Allen Toussaint, etc. In a nice bit of timing, the album was nominated for a Grammy Award on Wednesday in the category of best traditional folk album.

So, now, the Drops are headlining bigger rooms.

“Yeah, getting signed to Nonesuch, with its status, and having Joe produce, that definitely got the attention of more people,” says Flemons.

“But I also think we got more popular this year because we’ve broadened the sound, and showed audiences that we could bring the string-band sound to another level,” he adds by phone from a tour stop in Montpelier, France.

Indeed. The mission of their previous discs was to introduce the black-string-band sound to the uninitiated, and to demonstrate its vitality, musicality, and its rock-ribbed roots in such a strong, rich tradition.

“So, once we’d accomplished that, we decided this album was the one where we would present a broader repertoire, and incorporate songs from other genres, and maybe try some new things,” says Flemons, the only member of the Chocolate Drops who is not a North Carolina native — he’s from Arizona originally.

“We knew that, until now, people had only seen a small picture of what we could do, at least in the studio - we’d already been playing some of these songs in our live shows for a bit.”

He’s referring to concert favorites like the high-stepping “Cornbread and Butterbeans,” the sassy and brassy “Hit “Em Up Style,” and the languid and sensual “Why Don’t You Do Right.”

At this point in their musical expansion, the Chocolate Drops are also enthused about bringing string-band sound, and aesthetic, to contemporary songs. On “Genuine Negro Jig,” they do that by reinterpreting Tom Waits’ “Trampled Rose,” and the aforementioned “Hit “Em Up Style,” which was originally a modern-R&B song released in ’01 by Blu Cantrell that bounced to a beat-box groove.

“Yeah, the creative process for us on that front has been pretty organic,” says Flemons. “Those tunes just sort of ‘showed up.’ I’ve liked ‘Trampled Rose,’ ever since I first heard it on his ‘Real Gone’ album (’04), and Rhiannon just thought ‘Hit ‘Em Up’ was a great song, and really wanted to sing it.”

And she sings the hell out of it. Given her opera-singer training, it’s no surprise that Giddens has powerful pipes and impressive range, but in the context of the Chocolate Drops, she checks her classical-music “rules” at the door, and sings it in sly, slangy but assertive fashion, employing the kind of phrasing that evokes ‘20s and ‘30s-era female blues singers.

In fact, on “Why Don’t You Do Right?” — a song that began its life as the Harlem Hamfats’ “Weed Smoker’s Dream” in 1936 and was a hit for Peggy Lee a few years later — Giddens almost brings a dreamy, murmuring Billie Holliday quality to her performance. Although, in the liner notes, she also cites Jessica Rabbit as an inspiration.

The three group members first met in 2005 at the Black Banjo Gathering in Boone, North Carolina — a meeting of scholars and musicians with a passion for exploring the African origins of the banjo, which evolved from the Malian ngoni and the Gambian akonting — and which Giddens learned to play while on a cultural exchange with Gambia.

They’ve described that experience as “life-changing,” and when the three met, they discovered they were kindred spirits with a love for both the music and its place in history. They then continued their “studies” by hooking up with North Carolina musician Joe Thompson, now age 90, who was regarded as the last of the old-time black-string- band players. He agreed to tutor them, and it was his mentoring that shaped the Chocolate Drops. And much of his music is now preserved in their songs.

“It was the kind of musical knowledge you really can’t learn any other way,” says Flemons — “other than learning it from someone like Joe who’s been doing it for such a long time - someone who has been so completely immersed in this tradition.”

Kevin Ransom is a free-lance writer who covers music for AnnArbor.com. He can be reached at KevinRansom10@aol.com.