Michael Dervan marvels at Elliott Carter's work at the weekend's celebration in London's Barbican

Elliott Carter is the elder statesman of new music in America. He was born in 1908 and got to know that great pioneer of American experimentalism, Charles Ives, while still a teenager.

He was turned on to new music by hearing Stravinsky's Rite of Spring when the work was scarcely a decade old. The conductor was Pierre Monteux, who had conducted the Paris premiere in 1913. Schoenberg, along with Stravinsky, was an important influence on the young American, who sought to bring together in his own music the expressionism of Schoenberg and the rhythmic deftness of Stravinsky.

Carter was one of those Americans who learnt their craft the hard way, under the tutelage of Nadia Boulanger in the Paris of the inter-war years. Boulanger's perfectionism honed his own idealism. He has sought to find a way of writing music that could radically confront the complexity of life in the 20th and 21st centuries.

At 97, Carter is still amazingly sharp, revealing at the weekend's BBC Symphony Orchestra's Get Carter! celebration a joie de vivre that would have done credit to a man half his age. Carter lived through the first World War. He sat beside George Gershwin at a performance of Berg's Wozzeck in the 1920s. He remembers the conductors Serge Koussevitzky and Leopold Stokowski as staunch advocates of adventurous new work in the 1920s (a decade, he says, when contemporary music in the US more easily won the support of public funds than it does at present). He retains strong sympathies from his European training, although he remains individually American in outlook. And, for more than half a century he has produced a stream of demanding, complex, information-packed, ultra-expressionist works which have startled and baffled as many listeners as they have thrilled.

The composer himself had a hand in shaping the Get Carter! programmes at the Barbican Centre, placing his work in a select context of pieces by Debussy, Bartok, Ives, Schoenberg, Copland and Sessions. Stravinsky got his nose in through a student performance in the Guildhall School of Music and Drama. Colin Matthews was featured through two orchestral tributes (one for Carter), and Elizabethan madrigals were threaded through a programme of Carter's choral music by the BBC Singers.

Carter's work is unusually demanding of his listeners. It's not that his music presents the most complex of surfaces or that it is, in terms of raw sound, the most challenging you're likely to encounter. Nor is it that his compositional strategies are hard to grasp.

It's rather that the listener is presented with a simultaneous multiplicity of messages, each of which can seem to demand an equal level of attention, rather like a split-screen movie with, say, four or more segments progressing on independent though related trajectories. In explanation of his work, the composer has offered an analogy with plants. A leaf, though hugely complex at the micro-level, is readily recognisable as a leaf.

However, the experience of a musical journey with Carter - in works such as the Piano Concerto of the mid 1960s or the Double Concerto for harpsichord and piano with two chamber orchestras (1961) - is tempered by a kind of teasing of the attentive ear, which tends to wilt under such a heavy-duty stream of significant information and suffer a degree of defeat in handling the imbalances between the solo parts of the Double Concerto.

Carter is a high idealist in the way he compresses content and layers it with painstaking craftsmanship. He probably needs a flawless chain of communication, from performer, through venue and acoustic to listener. In my experience of last weekend's concerts, this ideal was felt with real strength in only a handful of works.

Emblems, a 1947 setting of an American Civil War poem by Allen Tate (1899-1979), for male voices and piano, was grave in its sweep and imperious in its passion under Stephen Cleobury, with stunningly incisive piano playing from Iain Farrington. In the Variations for orchestra (1953-55) (the BBCSO under David Robertson), the expressionism seemed to be ignited with a special dark fire, helped by an extra deep glow in the harmony and a greater than usual tautness and cogency in melodic shape. The First (1950-51) and Fifth (1995) String Quartets (from the Arditti Quartet) had an extra lucidity that befitted chamber music in a largely orchestral weekend.

And the most recent work, Of Rewaking (2002), a setting of William Carlos Williams (with mezzo soprano Jane Irwin), showed Carter almost relaxing into a new directness and pliancy. The closing lines sum up an important ideal.

"The instant/trivial as it is/is all we have/unless/things the imagination feeds upon,/the scent of the rose,/startle us anew." Carter is ever striving after the new - he is still composing - and it was startling to realise what an effect his music was having on the perception of other composers' work. Everything else seemed simpler and straighter in the comparison, sometimes even too simple and too straight, after the mind had been stretched and stretched again by the Carter touch.