In the last four years or so some of the most successful female country singers have turned their backs on the formulas that made them chart fixtures: Patty Loveless experimented with a more acoustic, bluegrass-flavored sound on her last three albums, and Lee Ann Womack’s last record was filled with old-school honky-tonk ballads complete with unhappy endings. Maybe it’s coincidence or proof of a trend among women hitting middle age in a youth-dominated market, but Martina McBride joined that company late last year with Timeless (RCA), a stunning collection of covers. The album’s stuffed, with 18 cuts of vintage honky-tonk, Bakersfield twang, weepy countrypolitan, and protofeminist sass originally recorded by the likes of Hank Williams, Loretta Lynn, Ray Price, Don Gibson, Tammy Wynette, Johnny Cash, and Connie Smith. The production isn’t retro, but it resists the rock-fueled sound of contemporary country, and though McBride doesn’t really add anything new, she does cut straight to the essence of each tune. McBride’s followed a distinctive path since the early 90s–starting with her anti-spousal abuse declarations in “Independence Day”–but this is the first time she’s pushed hard against Nashville’s strictures, and the fact that a collection of stylistically authentic country covers sounds radical says volumes about the current state of Music Row. Sun 1/29, 7:30 PM, Rosemont Theatre, 5400 N. River Rd., Rosemont, 847-671-5100 or 312-559-1212, $54.75-$69.75. All ages.