As First Aid Kit, Johanna and Klara Söderberg have a habit of making people cry. Not just fans of their dreamy spin on Americana, but also famous folks. There was that time they performed “Dancing Barefoot” in front of its author, Patti Smith, at the Polar Music Prize awards ceremony in 2011, and the camera caught Smith with tears in her eyes. A year later, at the same event, they sang “America,” and Paul Simon rose from his seat to applaud, similarly misty-eyed.
The Söderbergs are still in awe of those moments, not quite sure how all of this has happened to a band with such humble origins. Their debut, “The Big Black and the Blue,” came out in 2010, and four years later they’re the toast of the indie-folk community.
“We’re still so surprised. It’s all crazy,” Klara says recently from a tour stop before arriving at the Paradise Rock Club on Sunday for a sold-out show. “That’s really how we feel.”
“We’re not putting anything on,” Johanna adds on the other end of the line. “We’re just two regular people from Sweden, and we’re constantly overwhelmed by all this. In a good way.”
Johanna, 23, and Klara, 21, are sisters who were born and raised in Stockholm, which is irrelevant once you hear the music they make as First Aid Kit. High and tight, their harmonies come from a long lineage of siblings who knew how to meld their voices to devastating effect, from the Andrews Sisters to the Louvin Brothers.
First Aid Kit’s songs, sung in English, are rooted in vintage folk and country traditions, but the band is in fact a modern reflection of how different strains of music come from all corners of the world now. Klara and Johanna just happened to grow up loving generations of musicians grounded in the American folk idiom, from Joan Baez and Buffy Sainte-Marie to Conor Oberst and Fleet Foxes. They’re all artists whose legacies have seeped into the Söderbergs’ own musical DNA.
Emmylou Harris was another guiding light for the sisters, who wrote a tender tribute to Harris and the bond she had with the late, great Gram Parsons. “I’ll be your Emmylou/ And I’ll be your June/ If you’ll be my Gram/ And my Johnny, too,” goes the chorus to “Emmylou,” alluding to another famous first couple of country music, Johnny Cash and June Carter Cash.
Harris ended up hearing that song and met up with Klara and Johanna in Stockholm. The meeting was sweet, and perhaps just a little surreal. “She said to us, ‘Are you the girls who made me famous?’” Klara says, and they both giggle.
“Emmylou” was a standout track on 2012’s “The Lion’s Roar,” First Aid Kit’s second album and the one that became their breakthrough. Their rise is likely to continue with Tuesday’s release of “Stay Gold,” their new album of pastoral ballads and joyful odes to being young and restless.
Working again with Mike Mogis, the producer closely associated with Bright Eyes and Rilo Kiley (and also a member of Monsters of Folk), the Söderbergs stayed true to their talents on the new album. “Stay Gold” gently tweaks their formula, supplementing it with fuller choruses, majestic string arrangements, and bridges that hit glorious peaks. With its swoon and sway, the opening “My Silver Lining” is the kind of song that beckons you to hop in your car for a long road trip.
The album also flickers with some of their most heartrending tunes, too. The spectral glow of “Shattered and Hollow” unfolds with a mix of resignation and resilience: “I am in love, and I am lost/ But I’d rather be broken than empty/ I’d rather be shattered than hollow/ I’d rather be by your side.”
The mystical stardust of “Cedar Lane,” set to an almost waltz-like amble, sounds like something Dolly Parton would have sung back in 1967, her hair piled high and a little catch in her voice. (The Söderbergs like that image: “I would love to hear Dolly Parton sing that song,” Johanna says, to which Klara adds, “I’d love to hear Dolly Parton sing anything.”)
“Cedar Lane” tells the story of two lovers in happier times, only to realize it’s all but a faint memory. It ends with an open-ended question: “How could I break away from you?” sung low and slow at first but then in an eruption of emotion, as if they’ll get an answer if they keep asking.
“That song is about being haunted by the past but also not really wanting to let go of it. . .,” Klara says, her voice trailing off. “I don’t know what else to say because I kind of don’t like talking about our songs. We just want you to hear it.”
‘We’re not putting anything on. . . . We’re constantly overwhelmed by all this. In a good way.’
“We like to keep a sense of mystery,” Johanna interjects.
Less mysterious is the fact that First Aid Kit has amassed a devoted following in a short amount of time, taking them out of the family home where they first performed and into packed venues night after night.
“It’s kind of a strange life, but it’s also such an opportunity. I mean, we get to play music for a living,” Klara says, yet again amused and surprised.James Reed can be reached at firstname.lastname@example.org. Follow him on Twitter @GlobeJamesReed.