Lars Ulrik Mortensen was once convinced he would be a rock star. Then he heard the harpsichord, he tells Arminta Wallace

If they gave prizes for enthusiasm, the Danish harpsichordist and conductor Lars Ulrik Mortensen would win them all. But classical music doesn't work like that. Instead, it gives prizes for excellence - and oddly enough, Mortensen has won one of those as well, in the shape of the 2007 Léonie Sonning Music Prize.

Apart from the fact that it comes with a very useful €80,000 cheque attached, the prize confers membership of an almost unimaginably exclusive club. It was first presented in 1959 to Stravinsky - yes, that Stravinsky - and has in recent years been given to Yo-Yo Ma, Alfred Brendel and John Eliot Gardner. "I have come into very distinguished company, that's for sure," says Mortensen, who says he had "no idea" he was in line for the award and isn't convinced that he deserves it.

On the other hand, he says, he is happy to accept it on behalf of those who, like himself, are dedicated to the exploration of historically informed performance. Or, as he likes to call it, "new music".

"I never use the words 'authentic', or 'original'," he declares. "As far as I'm concerned, and I think also [speaking for] most of my colleagues in this field, it's not about creating a museum. We create music of former times for - well, for now. I don't think anybody has actually said it better than Roger Norrington. When he recorded the Beethoven symphonies for the first time with historic instruments and Beethoven's tempi and so on, he said that the whole point of using old instruments is to make the music sound new.

"That reflects quite precisely what I think the purpose is of this 'movement', if you want to call it that. Of course we use historic instruments, or copies of them, and we try to be very aware of the playing techniques, principles of ornamentation, rules of figured bass - and so on - that applied when the music was written. But we see those as tools, not as an end in themselves. It's about creating new sounds and trying to explore hitherto unknown areas to create a music of today which - hopefully - is as fresh and as spontaneous and as vivid as it was when this music was heard for the first time."

Irish audiences will get a chance to judge for themselves just how successful Mortensen has been in this area of endeavour when he performs with the European Union Baroque Orchestra at St Canice's Cathedral on Friday, August 18th. A long-time associate of the group as harpsichord tutor and guest conductor, Mortensen was appointed music director of EUBO two years ago.

A training initiative aimed at young Baroque musicians who are about to embark on professional careers, it invites applications annually from all EU countries. Applicants attend a selection course during which they are tutored by some of the best-known names on the Baroque circuit; at the end of this, 20-25 of the best young players are chosen to form the orchestra for the rest of that season.

"This process makes for quite exciting times for the musical director," says Mortensen, "because until April we don't know what the orchestra is going to be like - even though the planning of concerts and programmes has been finalised long before. For instance, if we have a bad oboe year or a bad viola year . . ."

Do they often have a bad oboe year? "Actually, in my time as musical director I do not remember any bad years," Mortensen says.

HIS OWN MUSICAL journey began when he first climbed on to a piano stool at the age of three. He specialised in music at school, sang in the Danish Radio Boys' Choir, and spent his teenage years playing with a rock band by the name of Culpepper's Orchard. "As a teenager I was convinced that I would become a rock musician," he says. "I played all sorts of keyboards of 1975 vintage - Hammond organ and Moog synthesisers, all that. But then, at the age of 20, I stumbled upon the harpsichord. I came across the famous anthology of Elizabethan keyboard music called The Fitzwilliam Virginal Book.

"I had grown up with classical music, so I knew my Bach and my Handel and my Mozart and my Schubert - but I hadn't actually gone much further back than that. And this music simply hit me like a hammer. I was fascinated by all aspects of it. Its harmony, its rhythm, the improvisatory elements - which I had not, until then, associated with classical music, but which I knew very well from rock and jazz."

His eclectic musical background is not, he says, something he wishes to over-emphasise. But in its own way, it colours his approach to the music of the Baroque period.

"The music of Bach's time was notated a little bit like rock and roll is notated today," he says. "I mean, you can go and buy the printed music of any rock band - but you will also see there that without a knowledge of what is meant by the notation, the notation itself conveys very little. The written music is a form which needs to be filled out: and you can only fill it out by an immense and very thorough knowledge of all the aspects and parameters of this music which composers did not write down, because they wrote for people who knew the style as well as they did themselves."

THE DISTINCTIVE SOUND of the harpsichord also played a big role in Mortensen's conversion to the early music cause. "It was the only keyboard instrument I hadn't played until then, and - well, I guess I simply found my sound," he says. What was it about that sound - which sometimes strikes the uninitiated as somewhat arid - which appealed to him?

"The combination of rhythmic precision with endless refinements in micro-timing, sound, and colour," is the impassioned reply.

"Also the fact that a harpsichord is not a harpsichord, of course. It can be an Italian harpsichord, it can be a 17th-century French instrument, it can be an 18th-century French instrument or an 18th century German instrument. It can be a virginal, it can be a clavichord. There's a wide, wide range of instruments which all contribute in a very particular way to the music that we choose to play on them."

For the Kilkenny concert, he'll be playing a double-manual harpsichord which belongs to Malcolm Proud - who performed with EUBO himself when it appeared at the Kilkenny Festival in 1997. As for the programme, it's a Baroque extravaganza.

"The emphasis is on the diversity of styles within a unity," says Mortensen. "We call it 'Europe in Harmony'. We have German music with Telemann, French music with Rameau and Muffat, English music with Handel and Italian music with Vivaldi." And, he promises, there will be a few surprises. "There are some tremendous repertoire discoveries to be made within this period. I personally like to surprise people a bit - to strike a balance between the familiar and the exotic."

The European Baroque Orchestra will perform in St Canice's Cathedral, Fri, Aug 18, as part of Kilkenny Arts Festival