Old Crow Medicine Show aren't revivalists. They're anachronists. On their fourth full-length, produced by Don Was, the Nashville quartet mash up a well-nigh 19th-century sound — hopped-up folk, bluegrass, country and gospel — with lyrics that are firmly planted in the 21st century. "Huff paint, cocaine, playing chicken with a train/Smack dab, meth lab, mellow out, rehab," hoots Ketch Secor in "Alabama High-Test." Several songs cast a journalistic eye on hard partying, from the country-blues stomper "Methamphetamine" to the title track, a drug dealer's confession. OCMS' rollicking fiddle sawing, guitjo picking and harmonica huffing will appeal to jam-band fans and Prairie Home Companion listeners alike, and there's a deadpan charm to singers Secor and Kevin Hayes. But when the band gets too grave, it's heavy going: The album grinds to a halt with "Motel in Memphis," a dirge about Martin Luther King Jr.'s death. (Message: Assassination is bad.) They're far better when they play their old-timey music, and themselves, for yuks. "If you're not a folk singer/Then we'll all have a humdinger," Hayes drawls.