'It took up two and a half years of our lives," says David Dewaele, one half of Soulwax, the electro-rockers who all but invented the mashup. "It affected my psyche," he adds. "I'd become depressed, aggressive."
"And then," picks up his brother and musical partner Stephen, "we'd look at all this work and realise there would be no financial reward."
The Belgian duo sound as if they are describing a spell in a forced labour camp. Actually, they're referring to something far more gruelling: a brand new Radio Soulwax app called that contains 24 hour-long mixes, each accompanied by its own hour-long film. These films are living and moving re-creations of whatever cover art accompanied each track used in the mix (of which there are an average of 70). The idea came to the boys after they put together an hour-long mix called Introversy for Radio 1, made out of nothing but song introductions – about 500 of them.
The brothers have always been restively creative – whether releasing records via the cover of Mixmag, surfing the early noughties mashup craze with their 2ManyDJs guise, releasing an album with 522 characters in the title, or capturing the spirit of the last decade's electro scene with Part of the Weekend Never Dies, a documentary that took in a whopping 120 gigs.
Right now, I'm in Soulwax's London pad, in Shoreditch, for a private demo of the app. Vintage record-players and old issues of Sounds lie around. But there's hi-tech gear, too, including a recording studio upstairs and the biggest flatscreen TV I have ever seen. It's on this that I get to play with the new app, as the brothers serve jasmine tea, grapes and brownies.
Of all the mixes, Into the Vortex, a collection of "weird, synthy" music in the vein of Tangerine Dream, best shows what a labour of love this was. "For the video, we had the idea we would remake all 27 sleeves in the mix – in real time. So we had a warehouse with a set builder and found people who looked like the people in the original covers."
Each time a new track surfaces, the screen shows these people assembling themselves into something resembling the original cover, as background and props do the same. Then, as the track fades, a "machine" takes a snapshot and appears to print out the original sleeve. The effect is more than a little mind-boggling. "You don't want to be on bad drugs when you see it," says David.
Filming each mix brought a new challenge. For Jack in the Box, an hour of Chicago-house tracks, the brothers were faced with an intriguing problem: most of the sleeves were white labels consisting of nothing but text. So they looked at early videos of how people danced to Chicago house, and then made dancing characters from those letters. The result is a joyous jumble of fonts, with Es turned on their sides to look like spiky haircuts.
Elsewhere, we have Blue (sad songs), Pin Ups (which uses a visual rather than a musical theme, namely any sleeve with breasts on it), and Hardcore or Die, an hour of 80s punk in which the covers scream along.
Realising that getting clearance for all the samples would be a headache, they found a loophole and applied for radio licences, becoming an internet radio company instead. The upside was no tussles with lawyers. The downside was they couldn't charge a bean: the app will be completely free.
The pair still think it's been worth it. After all, it showcases parts of the music-making process that are in danger of becoming extinct: the beauty of sleeve art, for example, or the idea of sitting down and listening to music without distractions. The whole project also chimes with the music tome of the moment, Simon Reynolds's Retromania, which suggests that pop is now eating itself at such a pace that all we're left with is its regurgitations. The band agree with Reynolds's point that, over the last decade, innovative music has dried up, leaving the most groundbreaking developments to come from the technological side of things.
You imagine that, after all this work, the Soulwax boys are due a good rest – or at least a bit of time to work on something lucrative. But just as I'm leaving, David puts on Blue and glazes over as sad songs fill the room. "You know," he says, "I would really love to make a second volume."