Neo-folk or folkie rock music — "Americana," if we really must — is a thing right now. It's respectable, musicianly counter-programming to a pop/R&B/hip-hop/radio-country mainstream nexus that's not always as disposable as detractors like to think. This sound ranges from mainstream-on-their-own-terms Mumford & Sons to curious indie darlings Fleet Foxes, both of which I hold at arm's length. The best band of this mini-boom, to these ears, is the one that best negotiates both ends of the scene's commercial spectrum, the North Carolina-bred Avett Brothers, a trio whose mountain-laden acoustic foundation is bolstered by pop instincts and, often enough, rock-band assertion. The Avetts' new album, The Carpenter, doesn't have quite the sense of purpose as their 2009 breakthrough, I and Love and You, which opened with the band getting haircuts, packing the car, and moving to Brooklyn — posited as much as an ideal of "bigger and bolder" as a physical place. But it does have producer Rick Rubin, who added spine and warmth to the band's sound then and keeps those elements in place here. The Avett Brothers play their biggest local stage yet this week, taking to the Mud Island Amphitheatre on Friday, October 12th. Showtime is 8 p.m. Tickets are $37.