Classical: Steve Reich and Musicians Royal Festival Hall, London

Steve Reich's 60th birthday (today) was aptly celebrated on Monday when his own Musicians stopped off in London on a European tour. Performers worldwide have learnt a great deal in the past two decades about the cool passion necessary for the successful interpretation of such deceptively simple scores. But there's still nothing like the zeal and skill of Reich's long-serving percussionists, in particular. Bob Becker, Tim Ferchen, Russell Hartenberger - and the composer himself, who still makes occasional appearances - have matured together in some of this music for a quarter of a century; Garcy Kvistad has also been with the group for many years. Like all this team, they joyously, almost casually, make the near-impossible look easy.

A large house heard eight of the Musicians, joined by five singers from Theatre of Voices, the American group formed by Paul Hillier, who conducted the premiere run of Reich's video-opera The Cave. "Genesis XXI", extracted from this extended music-theatre work, was the first of two vocal items. At less than four minutes, though, this rapid-moving incantation for soprano, tenor and five players barely had a chance to register here.

The other vocal piece was Proverb, a setting - for three sopranos, two tenors and a pair each of vibraphones and electric organs - of a single sentence by Ludwig Wittgenstein that characterises the composer as much as the philosopher: "How small a thought it takes to fill a whole life!" Heard incomplete at last year's Proms, Proverb has been revised and doubled in length to form a three-part structure moving deftly from D minor to remote E flat minor and back. The gradually augmented canons for the sopranos remain, as do the tenor duets that openly acknowledge their debt to the 12th-century composer, Perotin. While the contrapuntal cunning is greater, the new version seems less dependent on the mechanisms themselves. The singers, however, were rather insecure and the impact oddly subdued.

If Sextet had concluded the whole concert, not the first half, I'm sure the audience would have gone away happier. Here, Steve Reich and Musicians were constantly alert to the subtle shifts of melody, harmony and texture, as well as rhythm, in a work that expertly dramatises a kaleidoscope of small changes in five contrasting movements. A pity that there were some problems with the amplification, as occasionally elsewhere in the programme.

The two-year-old Nagoya Marimbas is a tour de force for Becker and Ferchen: five minutes of pure, woody virtuosic delight in the sort of contrapuntal pattern-play that the composer has made so much his own. Electric Counterpoint, for electric guitar and tape, was brilliantly played by Mark Stewart, equally alive to the piece's poetry and punch. And we began where so many aspects of the composer's mature style were first revealed: with a brilliant, risk-taking and riveting performance of Drumming, Part 1 that made the rafters ring. Is Reich, as Phil Johnson wrote on these pages on Monday, a true 20th-century master? Of course he is. Happy birthday!

KEITH POTTER