MUSIC / Youth's a thing that will endure: Celebrating the music of the young: Schubert, Rossini and Roxanna Panufnik. Plus 'The Creation' on the South Bank

Though the art of the string- quartet is no longer confined to a handful of legendary names - the Busch, the Griller, the Amadeus - world- class ensembles remain thin on the ground. New quartets come and go in the tide of enthusiastic young performers flowing from our universities and colleges each year. But players such as the Alban Berg Quartet, appearing at the Queen Elizabeth Hall last Thursday as part of South Bank's Schubert series, are in a league of their own.

They were playing the G major String Quartet - written in 1826, when the composer was 29 - and the C major Quintet, completed two months before his death in November 1828, at the ripe age of 31. By coincidence, I had just returned from a brief Roman holiday, my head full of Shelley, Keats and the English Romantics. The juxtaposition brought to mind questions of youth and age, not only because, like these poets, Schubert forged breathtaking imaginative worlds in a cruelly brief lifespan, but also because these are Schubert's late works, relatively speaking. Though granted even less time than Mozart, he found his unique voice more quickly, and left fewer pieces of a humdrum, everyday nature. But our easy access to this music through recordings and concerts may leave us blase about its achievement. Crystalline performances like those of the Bergs renew our acquaintance with its molten core, one that is transcendent at every level.

The slow movement of the Quintet radiates this sensibility in its purest form. With the addition of cellist Heinrich Schiff (Schubert preferred the Boccherini-type quintet with two cellos to the Mozartian modal with two violas) the Bergs caught the very breath of this music, phrase by phrase. The scherzo had all the spontaneous freshness of Schubert's string writing, and the effortless sense of motion he achieved in these masterworks of his last years. Sometimes this motion has the rapidity of a whirlwind: the finale of the G major quartet moves in this way, and must count as the longest moto perpetuo in musical history. But it can also encompass a Brucknerian slowness. In the quartet's first movement, hushed paragraphs generated not stillness but a sense of suppressed energy. The tension was symphonic, yet based in extended repetition and variation, far removed from the symmetries of classical form.

Not that Schubert couldn't master these forms when he wished. His Octet, broadcast live on Radio 3 on Monday lunchtime, formed the St John's Smith Square debut of the Gaudier Ensemble, and an appropriate pendant to the South Bank's exploration of chamber music and song. For the work of a 25-year-old, it shows astonishing flair, outshining its model, Beethoven's famous Septet. The practical point of this work is the clarinet part, originally intended for an amateur clarinetist, Count Von Troyer. On this occasion Christopher Marks was the soloist, displaying a warm-toned lyricism in the second movement, and in the bubbling theme-and-variations, a generous technical control. String-playing was firm and impeccably tuned throughout. Mixed ensembles of this kind often enjoy a brief shelf-life. If the Gaudiers can overcome the besetting problems of repertoire, organisation and funding, they promise to go further than most.

Composers now usually take rather longer than Schubert to find a personal style, even if like Roxanna Panufnik they are from a distinguished musical family. As a student at the Royal Academy of Music she experimented with various kinds of minimalism. Now, in her 25th year, these investigations have borne fruit in the 'Flori Suite', given its London premiere at the Wigmore Hall on Sunday by the Florilegium Baroque ensemble.

Her first success has been in avoiding the strong temptation to emulate Stravinskian pastiche when composing for a group of period instruments. True, the opening idea, a chordal build-up on strings, promised just the opposite. But its emphatic banality was ironic, leading to desperate shrieks from violins and flute and grunts from double bass and theorbo, that turned the music inside-out and tore it to shreds in an extraordinary way. The work ended with a jig that took the process even further, blunt gestures replacing themes; a nebulous, pulsating opening in the manner of John Adams; a flurry of tone- clusters from the harpsichord. Midway the music stuttered to a halt, exhausted, before resuming its pattern of staged anarchy. The slow movement was less memorable, and less memorably played.

Still, full marks to the ensemble for trying. And please, must every baroque instrumental recital include the interminable Telemann? A suite by Georg Muffat was crisp, imaginative and individual. Why not more of him?

Covent Garden's Barber of Seville continues to hold the stage eight years after its unveiling. Monday evening's performance was strong in presence, weak in orchestral detail, which was ragged in the overture, and without much improvement thereafter. Thomas Hampson, making his Royal Opera debut as Figaro, offered a stirring Act 1 cavatina, with an excellent crescendo provided by conductor Evelino Pido. Rossini's later life is famed for its assortment of non- musical pursuits - mostly culinary. But at the age of 24 he was pretty good at writing opera too.