It’s always fascinating watching two people unabashedly in love play music together on stage. In the case of married couple Michael Trent and Cary Ann Hearst of Shovels & Rope, they keep their stage persona raw and engaging, never making their audience feel like unwanted Peeping Toms. A ragtag duo if there ever was one, the South Carolina-based band plays their haunting folk melodies on instruments they literally scrounged from trash heaps. Hearst’s voice elevates the band above all those other acoustic-couple duos — her voice is one of the best out there. It’s soulful, throaty and glorious. Listening to it will give you chills every time. Shovel & Rope’s Bartlett show is technically sold out, but a limited amount of tickets will be offered at the door.