Finding a band more popular than Mipso on the campus of UNC-Chapel Hill once seemed impossible. A trio of bright college boys playing pretty bluegrass, they inherited a throne vacated after The Avett Brothers moved to the major leagues. Like the album that came before it, though, their 2013 LP, Dark Holler Pop, was just serviceablepleasant, polite, tidy. But Mipso’s new two-song EP, Faces, offers their most tantalizing pair of tunes yet, thanks in part to newest member, fiddler Libby Rodenbough.

Rodenbough joined Mipso full-time last May after graduating from UNC. She’d played fiddle with the band before, but she wanted to do more than play behind the boys. “I love playing violin, but it’s not exactly my passion,” she says. “I always wanted to be a writer, and now that I’m doing music as a job, it seemed like a pretty good way to fit those things together.”

“Down in the Water” is the first tune she’s finished writing. It’s a smooth, ruminating number that goads Mipso toward more interesting territory. It’s also the first Mipso tune to feature drums, courtesy of Dan Westerlund (Canine Heart Sounds, Bowerbirds). A few electric guitar licks fit comfortably in the mix, too, enriching the band’s sound without overpowering it. “Love Again” reverts to Mipso’s signature lightness, which they embolden with organ, piano and drums. The sweet pop manages to sound grown-up, fully realized. The harmonies even teeter on the precipice of doo-wop.

Mipso hopes to keep integrating Rodenbough’s voiceas a singer, fiddler and writerinto its core. These songs offer an early indication that it’s a promising decision.