Then suddenly they began shouting in full riot-girl fashion and a saxophone broke out. We exploded into smiles. It was all at once an enthralling, uplifting and joyful outburst. "I really hope that's the band and not just a CD," said one of my friends. It wasn't a CD.

We hurried down the hill to find five girls clad in knee-length boots and futuristic grey and fluorescent yellow dresses. Those not on keyboards stomped furiously about the stage, keeping perfect pitch. They were clearly having a good time. Behind them skulked the male members of the band, on guitar and drums.

This was the Antwerp eight-piece Capsule, and their energy ensured that a constant stream of people made their way to the front of the stage to join those already jumping up and down appreciatively in the twilight sun.

Some of their songs, like "Ramschlager", were wild and fast, delivered in German. Some, like "Ain't No Jesus" were eerie, atmospheric narratives bordering on a choral tradition. Some had jazz-blues and swing elements like the surprising arrangement of the 1980s Rockwell song about paranoia, "Somebody's Watching Me". Most were in English, and all were catchy.

The added oomph of the sax and clarinet riffs and their ability to fuse styles had me believing that at least a few of the band were classically trained. But not so, according to Saar van de Leest, one of Capsule's three lead vocalists, who also plays clarinet and keyboards. "Not everybody in the band can even read music, but most of us come from very musical families," she tells me as we sit under the awning of rock bar Homey in Antwerp.

Van de Leest began playing the flute when she was eight. "But then I discovered boys, and they got in the way," she says, rolling a cigarette. I didn't pick up an instrument again for 11 years. When I did, it was a clarinet."

She and her good friend Florence Henry - lead vocalist and the band's sampler fiend - got together to jam in their early 20s. "We had both broken up with our boyfriends and thought, ‘let's go into the basement and make some music'," says Van de Leest.

The rest of the band came together organically, a couple of years after Van de Leest and Henry had created CDs of their compositions and were repeatedly being asked to perform. "We didn't want it to be just the two of us," Van de Leest says.

The band has been going five years now and has started its own label, Rotakt. "But we can't live from our music yet; we've all got day jobs," says Van de Leest. Judging from the sold-out suitcase full of CDs after the PleinOPENAir gig, it might not be long before they can.

10 September, 21.00
Kinky Star Vlasmarkt 9, Ghent

1 October, 21.00
La Campine Kempisch Dok - Westkaai Antwerp
www.rotaktrecords.be