Slumped in a dressing room above a Washington DC club, the three members of Future Islands look exhausted. Keyboard player Gerrit Wilmers mutters something about how he's "maintaining quite well", an assertion that would perhaps carry a little more weight if the man saying it didn't appear to be on the verge of catatonia. Singer Samuel T Herring, meanwhile, has contracted tonsillitis, adding an extra layer of sandpaper roughness to the already bizarre combination of soul-inspired testifying and death-metallish growling that constitutes his vocal style, and necessitating a course of antibiotics. "I want a beer so bad," he sighs, looking dolefully at my bottle of Sol, "and I can't drink, because I've got to get this thing gone."
It's not just down to their touring schedule, which makes you feel hysterical with fatigue simply looking at it, and which has left their van in a considerable state of disarray: when bassist William Cashion opens its door to fetch something, a bag of mouldy carrots falls on to the pavement. They've always toured like this, shrugs Herring, "just travelling around, making that 30 bucks a night, gas money to get us to the next place and have something to eat, hoping it keeps growing", deliberately playing towns in America where bands never play, because they grew up in a town in America where bands never played. The nearest venue to Herring's North Carolina home was three-and-a-half hours' drive away. Their exhaustion is also down to what Herring describes as "all the added attention and new fans and, er, old friends who didn't know what we were doing and now do".
Without wishing to detract anything from the years that the trio have spent slowly building a cult following, the added attention is clearly down to one TV performance. Until this March, when they appeared on Late Night With David Letterman playing their single Seasons (Waiting On You) - a performance that subsequently went viral on the internet - Future Islands were, as Herring puts it, "past ever being a thing". They had spent 11 years together, moving from North Carolina to the burgeoning indie scene of Baltimore, plying melancholy indie synthpop with a layer of weirdness added by the sheer intensity of Herring's performances, involving much literal chest-beating and what one might describe as dancing as if no one is looking. Their albums were often great - 2010's In Evening Air is particularly compelling - and well reviewed, but nothing about them seemed suggestive of potential mainstream success.
Their background was entirely uncommercial. Herring's introduction to music had come when he stumbled across his older brother's video collection aged 10: he alighted first on The Gift, the 1993 film made by Perry Farrell, which featured the Jane's Addiction singer "shooting up and having sex with his girlfriend after she'd ODed" and then, to make matters worse, a film about GG Allin, the late punk singer famed for performing naked and eating his own faeces onstage. "I did think, 'What's wrong with my brother?'" he laughs. "But I was also really intrigued. Like: 'What is this way of life?' It coloured the world for me, you know, you can approach life in a different way, you don't have to go down any particular path. And yeah, even if you throw shit at people they'll still show up to your gig." He frowns. "Perhaps you shouldn't quote that. That sounds bad."
Later, he wanted to be a performance artist, because they seemed "dedicated to something that has no monetary value": "I went off to summer school when I was 17 and the teachers turned me on to performance art and conceptual art," he says. "I came home and told my parents, 'That's what I want to do,' and they were so mad." Instead, he formed a band with Willmers and Cashion, Art Lord and the Self Portraits, a high-concept art-rock project in which Herring played an arrogant, narcissistic German frontman given to comical onstage pronouncements. This became a problem when Herring's lyrics started to take a turn for the soul-baring and impassioned. "People would go, 'That's funny,'" recalls Cashion, "and we were like: 'We're not trying to be funny any more.'"
So Herring stopped pretending to be a German and they changed their name to Future Islands. People stopped laughing and they developed a loyal cult following. And then they moved from Thrill Jockey to the august indie label 4AD, which secured them the Letterman slot. They had, says Herring, "no expectations beyond blowing a few dads' minds, guys sitting at home, drinking scotch, going: 'What the hell is this?'" In front of the cameras, Herring did what he usually does, pounding his chest with his fist so hard you could hear it over the music, reaching out to the audience as he sang, trying, "to open up the audience by opening up yourself . . . The feeling we're trying to create in our shows is to kind of poke at people. It's just like, Move! Get going! Do something! Feel something, take my hand, hold on to that person beside you, feel this energy."
He noted the audience looked quite excited and Letterman himself was hugely enthusiastic, but the trio didn't think any more of it until a week later, when a friend of Cashion's emailed him to inform him that the performance had gone viral on YouTube. "It just went up and up and up. We were like: 'What the hell is going on?' These celebrities started retweeting it. Coldplay retweeted it." At last count, it had been viewed 1.8m times, turning Herring into an unlikely sex symbol: in Washington, whenever he busts a move onstage, the air is rent with female screams. I'd expected him to be embarrassed by this, but, rather winningly, he appears to be chuffed to bits.
That notwithstanding, a hint of what-the-hell-is-going-on still hangs around Future Islands: after all, but they didn't do anything special in front of the TV cameras, they just played the way they had played on countless tours of tiny venues. But from an outside perspective, its appeal is obvious. On the most prosaic level, Seasons (Waiting on You) is a fantastic song, from what's audibly Future Islands' best album yet: Singles is, as Cashion puts it, "full of awesome full-on jammers".
Moreover, in a world of "meh", here was a performance that seemed to have a genuinely polarising effect. People either seemed to love it or find it completely excruciating for exactly the same reasons: its obvious, unmediated sincerity, its disregard for accepted notions of what constitutes onstage cool. "People think that the only music that has that kind of emotional weight is like, you know, head down, clutching a guitar," says Herring. "It's good that people are compelled to watch it, and give it a chance. It's funny that there are people on social media who are actually sort of mad at themselves, they apologise that they don't like it.' I really want to write to them, and say: 'It's OK, it's music, if all your friends like it, that's OK. Go find something you like, you're not hurting our feelings.'"
He laughs. It's not that they're not enjoying it, he says, it's just that it was so unexpected. "You know, we were happy to be this journeyman band who just continued to grow and put out great records and cared about their fans and worked hard. It was just the three of us against the world. And now it's like, there's . . ." he searches for the right word. "Bigger," he smiles.
Singles is out now on 4AD