Gidon Kremer has pale but piercing eyes. Or rather, his eyes, gazing out from behind neat, wire-framed specs, do not so much pierce as seem to pin you against the wall. The Latvian violinist is very intense, and does not laugh very much. He is also tired. He got up at three in the morning to catch a plane to London from his home in Paris for a two-hour rehearsal. In an hour or so he will take another plane to Milan.
"I am thinking about my young daughter who is seven, and who plays the piano," he says. "I don't know if I want her to lead such a hard life as I do. I wouldn't wish a day like this on anyone." But this hard life has a good side, for us at least. Without Kremer, many music-lovers might never have heard of two great 20th-century composers - Alfred Schnittke and Astor Piazzolla.
Born in 1947 in Riga, Kremer grew up in Latvia before moving to Moscow to study under the violinist David Oistrakh. He was the child of violinists, both of whom had their careers blown to the winds by the second world war. His Jewish father survived the Holocaust by hiding in a Riga cellar for two years, and the young Kremer was groomed to fulfil his father's frustrated ambitions. That was not his only burden. "Growing up in a totalitarian regime, I also had to endure the pressure of the state ideology. It was hard, trying to be a free artist."
Nevertheless, Kremer flourished musically, winning numerous prizes. The most important was the 1970 Tchaikovsky competition, where conductor Herbert von Karajan was moved to call him "the greatest violinist in the world". For the next 10 years, until he finally left the Soviet Union, Kremer struggled against the regime, risking his career promoting the music of seriously out-of-favour composers - Schnittke and Arvo Part among them.
"If you wanted to perform music that you loved and believed in but was not written in a socialist-realist style, you got into trouble," he says. "Schnittke's music was not forbidden but there were very few artists willing to risk their careers to present it. It took some efforts." Schnittke's fourth and last violin concerto, written in 1984, was dedicated to Kremer. The composer and violinist's initials, translated into musical notation, formed a framework for much of the work.
One of Kremer's other great enthusiasms, the work of the Argentine Astor Piazzolla, has led to his recording six CDs of the composer's music over the past four years. Piazzolla, who studied composition in Paris under Nadia Boulanger, and returned to Buenos Aires to breathe new life into the tango, died in 1992 little known outside South America. Now he is intensely fashionable; performances of his heady, complex tangos proliferate.
Though Kremer does not shy away from the traditional repertoire - he was in London to rehearse the Sibelius concerto - his sense of adventure is at the heart of his identity as a performer. He is an explorer on the borders of the known musical world. "For me it would be too boring to play music by only dead composers or to present music as if it were in a waxworks museum," he says. "I don't want music to be a matter of comfort but of expansion of the spirit."
Kremer's interpretations of Piazzolla have been criticised for being too coolly postmodern and tame, for not reeking strongly enough of the sweat and smoke and sex of the world of tango. Maybe so, but Kremer will never give his audience an easy ride. He can produce sounds as soft and creamy as fresh butter, then jolt you with crash landings and emergency stops. His violin does not merely sing; it strains and rasps and rattles and groans. "One of my favourite conductors, Nikolaus Harnoncourt, says, 'Don't strive for perfection, because perfection is in conflict with beauty.' I would say that my role is to deliver something of beauty. Not ordinary stuff. Not something that is merely perfect."
Does he agree that he plays at the very limits of his physical ability? "Being on the edge, being on the border, being extreme - this is correct," he replies. "I know so many colleagues who deliver great performances on the scale of technique. But very often behind it there is an empty message, or no message at all."
Just as Kremer's playing occasionally strains, so too do his words. You feel that his mind is roaming free and that language - or at least English - cannot quite contain it. But then Kremer, who has lost his childhood fluency in Latvian but speaks Russian, English, German and French, believes that music is also a language, and one that can express emotion in its rawest form.
This is crucial when it comes to selecting repertoire. It attracted him to Schnittke and Part, and more recently to the Georgian composer Giya Kancheli. He talks about music with a "human heart". "This is what drew me to Piazzolla," he says. "He has the same sense of beauty and nostalgia that Schubert had." It is typical of the connections that Kremer makes that he should talk of a 19th-century Austrian and a 20th-century Argentine as if they were contemporaries, even friends. "I am attached to music that speaks to you and does not just manipulate your sophistication. The point is not only to say something unheard of before but to say it in a language of emotion. Music can be a mirror of ourselves. It offers us the opportunity for reflection.
"Occasionally the audience is not aware of the precious things that are presented to them," he says sadly.
In 1997 Kremer set up the Kremerata Baltica, an ensemble of young musicians drawn from the Baltic states of Latvia, Estonia and Lithuania. This move is not merely musical or personal. "To defend their national identities and to do something good for the music of those countries - this is certainly political," he says. There is a poetic justice to it - after all those years of being identified as a Soviet or Russian violinist, Kremer is staking out a territory of his own.
He works with Kremerata Baltica for about five months of the year. "They are still fresh, still far away from the routine of many orchestras that are really only to do with money-making." One of their recordings, of works by the Latvian Peteris Vasks, contains a note by the composer about his 1991 piece Balsis. He writes of "the Soviet empire's dying excesses and the peaceful resistance of the Baltic peoples".
This does not mean, however, that Kremer regards Latvia as the place where he belongs. Championing the music and musicians of the Baltic states (he has recently recorded a disc of contemporary Baltic music called From My Home) does not provide "an ID of myself. It is part of my past, and I pay tribute to it, just as I pay tribute to other parts of my past. A big part of my life is to do with Russian culture."
So where is home? "I have lost the sense of home. It is very dispersed, it is very vague. It is here," he says, tapping his head. "It is more the idea of a creative process in which I feel at home. It is an internal landscape. Inside this home I know all my shelves better than I do the ones in Paris. When I return to Paris, I find that my books are not where I thought they were. The shelves of my mind are a little more ordered."
