What happened to duos? Once upon a time, hits came from Sonny and Cher, Ike and Tina Turner, Marvin Gaye and Tammi Terrell; if you scan the modern-day pop landscape, it’s tough to find equally powerful pairings. If there’s one area where the twosome hasn’t gone out of style, though, it’s near the intersection of country and folk: Groups like the Civil Wars (now-defunct) or Thompson Square continue to take advantage of the special textures offered by male-female harmonies, the unique way in which the voices can interlock and form something greater than the sum of its parts. For the listener, there's always a voyeuristic thrill that accompanies this music: Even if the singers are not romantically involved, their songs feel like a real-time record of a relationship, a rare chance for an outsider to peek into another couple's private world.

Daniel and Lauren Goans, who perform as Lowland Hum, could be connected with a long lineage of mixed-sex folk-inflected vocal tandems -- Ian and Sylvia, Buckingham and Nicks, Richard and Linda Thompson. The Goans -- who are married -- released their self-titled sophomore album this week, following their 2013 debut, Native Air. (They released three songs in between on the Four Sisters EP.)

For these two, folk is just a jumping-off point: Lowland Hum is a shifty album, full of songs that start off small and alone, relying mainly on traditional tools, but then build in sudden, unexpected ways.

The album opens with “Sunday,” which serves as both a palette-cleanser -- wordless hums, strings and a tentative beat swirl together in a gauzy mess – and a warning: This may not be your typical acoustic singer-songwriter stuff. “Olivia” spikes the verses with bossa nova, but transitions into a more straightforward beat for the pleading chorus. There’s a tough to identify, modern-sounding riff – verging on a synthesizer – during “Charleston.” “Older Wiser” gestures toward something barbed and driving, and the low, tightly-locked and slightly droney beginning of “Lautrec” evokes Nirvana.

Lowland Hum’s compositional technique may contribute to some of the unusual flavors on the album. In a recent interview, Daniel suggested that his songwriting process changed during the making of this album. In the past, he might bring a mostly finished skeleton of a song to his partner, at which point the two would flesh it out together. For this album, they tried to work clloser than they had in the past – each involving the other as soon as creative inspiration struck. Though Lauren doesn’t play the guitar, she can apparently visualize melodies in her head; Daniel then works to identify the key changes that bring her vision to life. This has its advantages: Not knowing the proper way to play an instrument means that you’re not beholden to established patterns in the same way.

And don't worry: Lowland Hum can shine with a traditional sound when they want to. “Nightdriving” is all clean strums, closely mic’d so you can hear the fingers squeaking on the strings as they change position. Lauren opens with a long held note, sweet and persistent: “Weeeeeee drive, into the dark.” The arrangement is open and easy, bordering on sunny but still refusing to be optimistic.

I don’t know where we are,” Lauren sings, “or when we’ll get there.” But soon the second voice joins for harmony, and the importance of the end destination is forgotten.