It's the first TV project for Sigur Ros frontman Jonsi & Alex Somers.

Jonsi & Alex, the side project of Sigur Ros' Jón Þór Birgisson and Alex Somers, are busy in Iceland supplying music for their first TV series, WGN's Manhattan.

Set in New Mexico during atom bomb testing in the early 1940s, Manhattan has become the duo's full-time job the last few months. They were in Los Angeles to meet with creator-writer Sam Saw and director Thomas Schlamme during the mixing of the pilot and will return to mix the 13th and final episode in about five weeks.

Sigur Ros Frontman Jonsi & Alex Somers to Score WGN's 'Manhattan'

"It's such a different challenge," says Jonsi, whose most significant film credit is Cameron Crowe's We Bought a Zoo. "When you do this kind of work, it's just so different from writing a song for yourself -- all the stuff that you have to keep in mind. It's a good challenge."

Manhattan, which stars John Benjamin Hickey, Olivia Williams, Daniel Stern and Ashley Zukerman, airs Sundays on WGN America at 10 p.m.

Their musical goal, says Somers, is for the "score to show a lot of restraint and not really be obvious except for maybe once an episode when you have to step it up a notch."

Jonsi and Somers spoke with Billboard from Reykjavik, Iceland, where they continue to work on Manhattan, are in the very early stages of the next Sigur Ros album and experiment with aromas derived from trees.

Scoring is so different from your work with Sigur Ros and your solo album Go. When you were hired, what did the showrunners request?

Jonsi: They like the soundscape of what we do.

Alex: Sam Shaw was hoping to get someone who wasn't a typical film composer. We don't have a lot of experience doing music to picture, so I think he was into that.

How is the approach different from Go or your instrumental album Riceboy Sleeps?

Alex: (Go) was a huge pool of songs written over many years and we were trying to take them and arrange them within his current headspace. Now we're just writing music, short blips of less than a couple minutes. We're not thinking about structure. It's definitely more heady, less intuitive, but we're trying to make it as musical as possible and not just score 10- to 15-second moments. We write music that can exist on its own and then edit it to fit in short cues. It's a learning thing.

Jonsi: There's a thrill in writing something so short.

Can you explain your working relationship with the filmmakers?

Jonsi: We ask them to only temp with our music when they do a cut of an episode, so they're pretty specific with what they want.

Alex: We have total creative freedom. They never say anything until we do a first run. We do whatever we want, then they come back with some specific ideas that maybe we haven't thought about. They'll give us direction on bringing out emotions of the characters.

What's next for you, either solo or for Sigur Ros?

Jonsi: We haven't been doing a lot, but we've got a new space. We're gonna get our shit together soon. There's always something brewing

Alex: Yes, always brewing. Jonsi has this workshop where he's taking branches from the forest outside Reykjavik and he's doing weird stuff. Jonsi has been making weird potions in this distiller machine he sticks branches in.

What concoctions have you come up with?

Jonsi: I'm basically really obsessed by smell. Really want to get some essential oils from birch and pine and angelica, but I haven't been really successful yet.

Alex: No, he's been good. He made some birch tar that was pretty cool. Make a fire and put a bucket over it and it drips this black tar basically. That was pretty intense.