Kurt Wagner’s compassionate, detached vocals come to the fore on Lambchop’s latest full-length, Mr. M, and his lyricism is as fragile as the band’s music is casually brilliant. Released earlier this year, Mr. M may be Lambchop’s finest record, and that’s saying plenty — after 20 years, the Nashville group has a rich oeuvre. On Mr. M, the band’s approach is as graceful as ever, with Mark Nevers’ production typically subtle. Over the years, critics have tried to characterize Lambchop’s sound — I’d say they have perfected a super-referential, slightly out-of-focus brand of pseudo-country-folk minimalist background music. Weirder than any countrypolitan crossover Owen Bradley could have imagined, they’re a great band. They’ve been on tour in Europe and stateside, and tonight’s show also features fellow Nashvillians The Altered Statesman, whose new EP-length collaboration with Wagner, Something Missing, is as sparely beautiful as Mr. M.