Everyone in his family in the Norwegian municipality of Eidsvoll played accordion. Any time there was a family get together, there would be at least 10 accordions pumping out polkas, waltzes and Schottisches, and when his father came home one day with a small accordion and announced that at eight years old young Stian was ready to follow in a tradition that goes back generations, the youngster's pleas that he be allowed to learn the piano met with a stern rebuke.
"My dad said – and let me get the translation right – the accordion was the grand piano of social democracy," says Carstensen with mirthfully staged gravitas. "I didn't know what that meant, so I just said, OK, I'll play the accordion. There was no choice. It's a family thing, like joining the funeral business."
Contrary to his instincts, Carstensen fell in love with the accordion. He was, he says, married to the instrument almost from day one. He even practised in the back seat of the car on the way to school and within eight months won his first competition. Within 18 months, he was wowing viewers of one of Norway television's leading chat shows with his fleet-fingered playing, allied to a sense of expression way beyond his 10 years.
"I'm not sure I can play any faster than that these days but I've learned a few things since then that have maybe added character," he says.
The accordion star now fronts orchestras and tears up the Balkans-inspired jazz of the band Farmers Market, who the late saxophone virtuoso Michael Brecker asked to play with, but all that once seemed unlikely. "When I was about 14 it became really embarrassing to play the accordion," says Carstensen. "My fellow teenagers made it clear it was a corny instrument, so I took up the guitar and for almost four years I didn't touch the accordion. I played guitar in rock bands and was going to be a jazz guitarist."
Jazz had been part of his training alongside the classical lessons he took on accordion from age eight, although it was dance music he played at functions with his father and other family members. "My dad liked jazz and I played with another guy who taught me about jazz harmony and improvisation, so when I left school I was keen to study jazz at Trondheim, which is where a lot of Norwegian musicians, like Tord Gustavsen and Trygve Seim, studied," he says. "I was going to play guitar but the guys who formed Farmers Market with me said, 'Hey, you play accordion, you should play it in the band.' I was quite surprised but actually really happy to start playing again."
One day, while rehearsing, the band came across the sheet music for a Balkan folk tune. It was tricky to play but Carstensen was smitten. Within two weeks he was visiting Bulgaria and learning more music first hand. He's subsequently visited the same area every year and still finds the idea of a living, working tradition fascinating.
"I'd heard some Ivo Papasov about the same time as I joined Farmers Market and I loved the idea he played weddings," he says. "Every Bulgarian wedding has this incredible, vibrant music that goes on for hours without flagging. But the other thing is my family originated in eastern Europe and I remember my father and grandfather being really interested in gypsy music, usually the sad tunes, so Balkan music must have been in my gene pool."
Balkan music will likely feature in the Celtic Connections concert that marks Carstensen's first visit to Scotland in his duo with English saxophonist Iain Ballamy. As with Farmers Market's meeting with Michael Brecker, Carstensen's hooking up with Ballamy, on a 2001 tour with former Loose Tubes maestro Django Bates's band, gave him a chance to play with a hero.
"I'd loved Iain's playing since I heard him with Bill Bruford's Earthworks in the late 1980s," he says, "and when we were touring with Django we started jamming backstage and found we could go anywhere musically either of us chose and it was great fun. So, we've now made three albums and do these concerts where we might play Chopin or a tango or a jazz tune or Teddy Bears' Picnic. It can be quite spontaneous but it's always tune-based. We don't bother about genre; we just love good tunes."
Stian Carstensen and Iain Ballamy appear at Glasgow Art Club on January 29