André Previn and Anne-Sophie Mutter: Zing went the strings

The conductor André Previn and his wife, the violinist Anne-Sophie Mutter, have cut a CD together. It's time to swing with Gershwin, they tell Michael Church

André Previn and Anne-Sophie Mutter sit side by side on the hotel sofa: birds on a branch, but of a different feather. Hunched in his woolly sweater, Previn comes across like a quizzical crow; the fifth Mrs Previn, erect and immaculate in silks, is more like a bird of paradise. Hand on knee, hand on hand, they seem a great advertisement for love's middle-aged dream, and to hell with the 34-year age gap.

To celebrate the union, they've made a suitably hybrid record, because Tango Song and Dance is not really any of those things. Previn's work of that name begins with a track in tango rhythm, but it is full of harmonic surprises. The "Song" track may be expressive in a terse sort of way, but "Dance" opens with a spiky cadenza suggestive of nothing so much as boogie on speed. After an incursion by the pianist Lambert Orkis – who accompanies Mutter in virtuoso pieces by Brahms and Kreisler – she shows her mettle in four transcriptions from Gershwin's Porgy and Bess.

The couple are adamant that we shouldn't regard this CD as a symbolic celebration of their marriage. In any case they go back a long way. To the Eighties, says Mutter: "Our first concert together was a Festival Hall benefit for deaf children, where I was playing and he was conducting." No, says Previn, further back, to a concert she'd given, aged 13, in Berlin: "I trudged backstage, as any fan would, but there was such a crush, I couldn't get near you."

There was a time when Previn himself was musical jail-bait: after dazzling guests with his Gershwin piano arrangements at a Hollywood party when he was 16, he was asked by Ava Gardner if he fancied taking her home. He refused, but soon learned to repair the omission, as the women he went on to marry found: Mia Farrow was the only wife who refused to put up with it and dumped him first. Mutter's previous marriage, to a lawyer who died of cancer, was by contrast an exemplarily private matter. She has presented an impenetrably professional façade ever since Karajan, who spotted her prodigious gifts when she was 13, took her under his wing.

The Kreisler tracks relate to her early childhood. "I grew up with these pieces, I have a very special relationship with them," she says. "My first teacher – who had to flee Berlin during the Second World War because she was part-Jewish – had played in the same coffeehouses as Kreisler. The pieces she made me play when I was six were the very same ones I chose for this recording. I found it amazingly difficult to get into the right mood – that combination of serenity and melancholy."

Listening to recordings of Kreisler himself, she was initially struck by how laid back he seemed. "There were lots of wrong notes, lots of old-fashioned slides. Only in my late teens, when I had become less fixated on accuracy, was I able to appreciate the quality of his playing. His sound was like a human voice, pure expressivity." Previn chips in: "He also had that quality that is now almost pejorative: charm."

What is the difference between violin-playing then and now? Mutter: "Music-making then was much more personal and eccentric, much more emotional." Previn: "I hear a violinist now – let's say on the radio – and I think, 'That's wonderful, I wonder who it is.' But if it was one of the old-time fiddlers, I would know who it was instantly." Mutter: "Since the violin is so close to the human voice, you'd think it would be the easiest instrument on which to create a singular voice, but we've lost that ability."

Mutter's website says that "music is not a business", though her CD covers show that she's not averse to personality-cult photography. But there's plenty of altruism, too, with a concert in Vienna next month in support of the Campaign Against Landmines, and two foundations she has set up to encourage younger musicians.

She sounds a resourceful tutor. "There's no one right way to approach a piece of music, because the variables are infinite. The only absolute requirement is that you must look at it anew. Listening to the recordings of colleagues can be inspiring, but copying is not the solution. One student I brought out of Beijing has amazing technique, but he has problems with the German repertoire. One day I asked how he arrived at a particularly fast tempo, and he said, 'I listened to a recording of Oistrakh, and he used that tempo.' I told him he had to find his own path – particularly hard for him, having grown up in a country where rules had to be followed. So I climbed mountains with him, made him read German authors, and brought him to Leipzig to see the church where Bach was in charge."

Mutter once confessed that she didn't think she had "the gene" for playing Gershwin. "It's because I'm European." Cue Previn again: "It's also about being a string player – string players count in a funny way, with everything in 12/8, instead of 4/4. As a conductor, I've often had to write out the score for my string players that way. They don't feel it the other way. You can take a great American orchestra and give them a Strauss waltz – and it just sounds wrong. It's correct, but it isn't right. Then you can take a British or German orchestra and try Gershwin – same thing, because they didn't grow up with it. But any kid in New York knows how Gershwin goes." Then he looks at her and softens. "But listening to you today, you sounded like you'd been on the road with Count Basie."

The couple are going to make their marital home in Munich: when not addressing me, they speak German. Does this reflect a return to his roots for the German-born Previn? Mutter: "He's much more German than you might think." Previn: "Jawohl! I still dream in German. And I've always said the alphabet in German – I can't do it in English. I've always done my basic maths in German. I miss America when I'm out of it, and I miss Germany when I'm not there. But what I most miss is you, Anne-Sophie, when you're not with me. So wherever you are, I'll go." At which tender moment the interviewer feels obliged to tiptoe away.

'Tango Song and Dance' is released next month by Deutsche Grammophon