It’s a special talent that can make the line “It’s going to get harder before it gets easier,” sound joyous, and David Wax Museum has that talent. On “Knock Knock Get Up,” the Boston-based troupe led by charismatic singer David Wax and donkey-jawbone-wielding cohort Suz Slezak weaves bright tunes from border-crossing folk threads. DWM doesn’t deliver straight Mexican or American traditions, instead steeping contemporary writing and performance styles in those influences for a fresh hybrid. The lyrics have matured, now as captivating as the sounds around the words. “The Rumors Are True” may not have the pop of earlier break-out “Born With a Broken Heart,” yet mesmerizes with mariachi blues and juxtaposition of a struggling romance and a meeting between a lamb and a wolf. DWM has leapt up the ranks of bands shaping contemporary folk. (Out Tuesday)

ESSENTIAL “Harder Before It Gets Easier”

David Wax Museum performs Sept. 21 at the Iron Horse in Northampton and Sept. 22 at the Narrows Center for the Arts in Fall River.