Nono: fragments of venice/Arditti Quartet/Mcfadden, Queen Elizabeth Hall<br/>Glass: Music in 12 Parts, Barbican, London

London is at the start of a six-month long celebration of the work of the Italian composer Luigi Nono (1924-1990). Fragments of Venice presents his work within the context of composers active in Venice, stretching back to Monteverdi and Vivaldi, as well as masters of the 20th century.

Nono's music is hardcore atonal. The Arditti became Nono's preferred quartet for Fragmente-Stille, an Diotima, written in the late Seventies. Its jumble of harshly dissonant, fluttering, chattering fragments coalesce in specific sonic gestures, frequently demanding unison of a kind from the four players. If this music has become easier on the ear, it's greatly due to the awesome confidence of the Arditti.

Nono's half-hour work followed Webern's Six Bagatelles – at a mere four minutes, a world of intense, compact, expression from which Nono appears effortlessly to pick up the baton.

In elegant programming, Schoenberg's masterly second quartet initially appeared to find the Ardittis less assured, less able to enter Schoenberg's wistfully romantic fading world. But the soprano Claron McFadden was able to capture superbly the mystery of Stefan Georg's portentous words.

Meanwhile, a festival of very different music at the Barbican. Philip Glass, along with his ensemble, has been widely celebrating his 70th birthday. Here, old and new compositions traced his once pioneering work to his virtual sell-out. Glass studied with the infamous Nadia Boulanger, but abandoned her rigorous Western didacticism for the lure of Ravi Shankar, the music of the East, and tonalism.

Glass's Music in 12 Parts dates from the early Seventies. It is to minimalism what Bach's Art of Fugue is to fugue. In an event lasting five hours, Glass and his amplified ensemble of three electric keyboards, three winds and female voice showed what his minimalism once meant.

It's hectic stuff, with no contrasting dynamics and no rests. The relentless demands in the 12 sections (three and a half hours of music) of rapid passage work in rhythmic unison make this not only perilous to play, but clearly young-performer music. The aching hands, the cramped shoulders and necks were obvious.

But this is Glass's seminal work. The hours passed painlessly in a faultless performance, Glass's psychedelic acoustic games exhilarating. The roars and whistles of the standing ovation from a packed house proved just how seductive minimalism remains – and how much more captivating than Glass's current sugary functionalism.

Nono: Fragments of Venice continues to 10 May(0871 663 2500; www.southbankcentre.co.uk)