Cary Ann Hearst and Michael Trent share practically everything. Aside from being married, they write engaging songs together as Shovels & Rope. And when the gothic Americana duo performs, they swap off on a drum kit, guitars and plucky vocals, sometimes singing on one microphone to boost the passionate intimacy. So it’s no surprise that they like to do phone interviews together, bouncing off each other in conversation like they do in their music.

Take the subject of happy hour gigs the duo played only a few years back in Charleston, South Carolina. “Kids were wandering around and taking a few bucks that were in our tip jar and running off,” Hearst says, while Trent pipes in, “Actually, babies were always the best tippers ’cause the babies liked to put money in the tip jar.”

The couple’s not hurting for tips these days. Shovels & Rope hit Royale on Sept. 26 and 27 after graduating to main stages at summer festivals like Newport Folk and cracking the Billboard Top 20 with their just-released third album, Swimmin’ Time.

“At first it was a little more separated,” Hearst says of their musical partnership, which grew out of sitting in with each other when they were billed under their own names on the Southern club circuit. “It was a challenge for us initially because there was a lot of our own personal ego to take out of it.”

That didn’t last. In 2008, the two musicians made a joint album called Shovels & Rope, a nod to the murder ballads they favored. They got married in 2009 and eventually committed to the band name Shovels & Rope, a move that gave them both a brand identity and ensured they wouldn’t have to work apart.

“About 400 shows into our career, we found ourselves fluidly going between each other’s songs,” Hearst says. “It kinda turned everything up on its ass so that now we’re virtually interchangeable within the band. I can’t play electric guitar like Michael, and he can’t hit some of my high notes. But we have flexibility.”

That means expanding their instrumental roles. Shovels & Rope have broadened and honed their palette since the duo broke out with their 2012 album O’ Be Joyful. The range of Swimmin’ Time, produced at home by Trent, kicks in early with four consecutive tracks. The garage-blues “Evil” mines similar territory to Jack White with its deep, distorted organ ballast. The ballad “After the Storm” more closely evokes Radiohead’s “Creep” in its chord progression and epic buildup, Hearst’s voice cracking with emotion. “Fish Assassin” swings as a snappin,’ stompin’ field holler, while “Coping Mechanism” finds Hearst and Trent tapping early rock ’n’ roll and doo-wop, their voices dancing in call, response and affirmation.

“The spectrum’s wider in both directions,” Hearst says. “Whether we tend to be a bit folksy on one song or have a heavier or more aggressive sound on another, the core of what we do is these narratives or imagery.”

The haunting final track, “Thresher,” even takes a humanistic angle, ruminating on the U.S. submarine of that name, which imploded off Cape Cod in 1963, taking all 129 members of its crew. Trent says he caught a History Channel piece and did research to write a song “trying to capture the feeling of what was going on inside the submarine when they realized that they weren’t coming back up.”

It’s all quite a growth curve for two musicians who inherited their first kick drum from a trash-picking friend. “That was part of our bar-survival method,” Trent says. “We started out with a tambourine and couldn’t get people to [quiet down] with that. And then we got a box to stomp on, and that wasn’t loud enough.”

In turn, they’ve also traded their old van for an RV that they share with their dog, named after Texas folksinger Townes Van Zandt. Hearst says, “Everyone that we love, that we live with, is with us all the time.”

Shovels & Rope play Royale on Sept. 26-27.