The singer/bassist revealed there are "skeletons of songs" and "bare rough demos" in the works and that the band has been utilizing their downtime at live venues to work on the new material -- "at sound checks, whenever we have time there."
The band is touring "indefinitely" throughout the rest of the year but is hoping to be able to head into the studio once that wraps.
While it's too early to divulge details of the new material, Sim says the next album will feature stronger vocals by Romy Madley Croft.
Romy's voice has grown a lot -- just from singing everyday. I hear it and it's beautiful to hear.
"That's one thing I can say," he stated.
The xx currently has no plans as to when they may release a new album, however, Sim explained that it could possibly be ready by 2014/2015 -- "or we might go home and have writer's block for a couple of years," he stated, laughing as he reached under the table to "knock on wood."
In addition to touring, the band is busy curating their own festivals.
"There's one in Berlin, one in Lisbon, Portugal and one in London. We're organizing everything. We chose the venues; we've chosen all the bands, all the DJs, even down to the food and drinks that are being served. It's amazing," says Sim.
The band is choosing a variety of eclectic locations for the shows. "Berlin's going to be in an abandoned theme park, London it's going to be in a stately home, Portugal is going to be in a castle by the water. It's a lot of work and we've got people like Solange Knoles and Chromatics, Kindness… Lots of good bands playing."
Though they aren't weighing out an American festival, Sim says he'd like to see how these three go before committing to any more. "It's been a lot of work," he jokes.
Sim also expressed his excitement over The xx being a part of "The Great Gatsby" soundtrack.
"It's something that we've wanted to do for ages and Baz's [Luhrmann] 'Romeo & Juliet' was one of Romy and my favorite films so we've been holding out and this was perfect. It was incredible. We worked with a 70-piece orchestra and Craig Armstrong who is an absolute legend in our eyes. The band will be missing the premiere due to touring obligations but plans to sneak into a theater on the road to catch a screening."