Cool fusion - The Kolacny Brothers

Stijn and Steven Kolacny are getting tantalisingly close to earning a place on that list of famous Belgians. Even if you haven't yet heard of the classically-trained brothers from Flemish Aarschot and their all-female choir called Scala, their ghostly covers of rock classics should be familiar.

Their sound, mostly just a slow-moving piano and about 20 voices bringing new depths to the overfamiliar, has become TV and movie shorthand for dramatic tension. They formed in 1996 as a traditional classical choir, then made the leap to rock covers and success in mainland Europe in the early part of the last decade - but it was only in summer 2010 that the world started listening.

Their mood-darkening take on Radiohead's Creep was used on the trailer for Oscar-winning movie The Social Network, now estimated to have been seen more than 250 million times. "We could literally trace our popularity to the views of that trailer," says younger brother Stijn. "That's real Hollywood power."

More recently, their minimal version of U2's With or Without You has formed the backdrop for the war and bow ties of ITV's Downton Abbey trailer, and will be heard again in a version by another singer bringing an operatic feel to rock music - Britain's Got Talent winner Jai McDowall will release it as a single and perform it with Scala at the Royal Variety Performance on December 5.
 
There are more major TV appearances still to be announced before Christmas, and Stijn informs me that they've just been heard on The Simpsons. The loquacious 35-year-old also pushes hard for me to write that their music would be the perfect accompaniment to the big-screen moping of the teenage vampires in the Twilight movies, which I will because it would. For now, a lower profile spot in the German all-girl bloodsucker movie Wir sind die Nacht (We are the Night) will have to do.

"Even a long time before The Social Network it was clear to us that this angelic sounding music fits perfectly to movies and television," he tells me. "But we're not a typical radio band."

It's true that their glacial sound would jar if played next to Fearne Cotton and the hyperactive R&B of the current charts, yet their albums reward total immersion. The self-titled Scala & Kolacny Brothers, a compilation of highlights from 10 previous albums that includes Kings of Leon's Use Somebody and Depeche Mode's I Feel You as well as hits by Foo Fighters, Oasis, Nirvana and Metallica, is the only one released in the UK so far. Three original songs by Steven, with electronic backdrops and a cover of Alanis Morissette's 1995 irritant Ironic, grate somewhat, but mostly they have a finely tuned ear for which songs will work in the format.

"It is a simple idea but it's not easy," says Stijn. "You have to be careful what you cover and what you don't. We have to keep a certain credibility. When we start interpreting really mainstream pop songs, Madonna or Robbie Williams, it gets really cheesy really fast."

They cite U2, Depeche Mode, Radiohead and Coldplay as personal favourites, but draw the line at anything much older. "Songs by The Beatles or Rolling Stones don't work for us - it's funny."

Modern R&B and hip hop is also out; too difficult to arrange. What's most interesting for them, and what makes for maximum listener appeal, are those times when a song acquires an unexpected new feel. Engel (Angel), by German industrial metal band Rammstein, is a fine example. "It almost sounds classical when we do it. When we cover a familiar song with minimal accompaniment, all of a sudden people start to listen again to lyrics that they knew by heart, and find different meanings."

There's a novelty element too, of course - the pleasure comes from the space between what the brain expects and the ears hear. Unorthodox cover versions are particularly popular right now, from the smiley high-school students of Glee, to the indie bands embracing pop on Radio 1's Live Lounge and the tearjerking Smiths song on that John Lewis Christmas advert. Scala's work doesn't benefit from similarities with recent choral adverts for Halifax and Lovefilm. However, other choirs have attained similar credibility, such as New York's PS22 Chorus of schoolchildren who have covered Björk and Phoenix, and the Crouch End Festival Chorus, go-to backing singers for artists such as Noel Gallagher and Ray Davies.

Scala provide more of a spectacle than a traditional choir too, as fans will find when they play only their second ever London headline show, at the HMV Forum next month. With Stijn conducting and Steven on the piano, the singers (usually between 15 and 20 of them picked from more than 200 they have on their books, all female and mostly in their early twenties) move around the stage and even into the audience while videos and lights add dazzle. "We're looking for a pure, emotional sound," says Stijn. "We're the opposite of the macho Russian Red Army Chorus."

Although both brothers are classical pianists and have released albums as a four hands duo playing the same instrument, it was rock fan Stevens who persuaded Stijn to throw in a cover of Garbage's I Think I'm Paranoid at a classical choir competition in Canada in 2001, and almost got them disqualified. "I thought it was a bad idea but I was wrong. I have to admit it," says Stijn.
Now they won't go back to their traditional roots. "Rock music is less complex, it's true, but that doesn't make it less interesting. It's just good music, and that's what counts."

Dec 13, HMV Forum, NW5 (0844 847 2405, kentishtownforum.com). The album Scala & Kolacny Brothers is re-released on Wall of Sound in a special edition with new tracks on December 12. The single With or Without You with Jai McDowall is out on Sony the same day.