There's a charming engraving in the British museum of music being made in Java 400 years ago. Three men armed with soft mallets are belabouring rows of gongs arranged in an open-sided square, with the big ones suspended vertically and the small ones cradled horizontally; a solid roof indicates the permanence of the installation. If you go into the gamelan room at the South Bank Centre, you will find, in essence, the same musical apparatus.
The gamelan is a newish craze in Britain, but in Bali and Java it has been the norm for centuries. A gamelan is often described as "one instrument played by many people". Its dozen players may occasionally give each other a nod or wink, but, essentially, each piece is built up by a rhythm felt in common, and by the intricate musical edifice they carry in their heads. In Java each gamelan is regarded as a living spirit, with its own name and home: the works played on it are felt to have lives of their own.
Two basic groups of instruments are involved: those consisting of keys (either resting on a wooden base or suspended above resonators), and gongs (which either hang or rest in rows on stretched cords). In addition, there's a bamboo xylophone, a bamboo flute, a 28-string zither, a two-string rebab (spike fiddle) - and the human voice. The biggest gongs are struck with padded mallets, the middle range with hammers made of wood, and the smallest are hit with buffalo horn: this makes for a delightful mix of textures, even though all the metal is bronze. In parts of Java, where bamboo grows luxuriantly, the gamelans are made of giant bamboo segments, and the sound has a different timbre.
Most pieces are cyclical; apart from the unmetred rhythms of the rebab and the human voice, faster parts relate to slower ones by powers of two; the melody underlying each piece can be either expanded or condensed, elaborated or abstracted by individual instruments within the texture. This complex and multi-layered texture has attracted Western enthusiasts including composers from Debussy and Britten onwards, and now groups all round the country.
"Treat them with respect," new entrants are told as they file into the South Bank gamelan room.In turn, they are invited to strike a xylophone: it is a magical sound. Then they can give the lightest felt-hammered tap to the biggest gong of all, and the floor vibrates to the slowest, deepest beat they've ever heard. And then they're off - teachers, journalists, computer programmers, all kinds of professional odds and sods - on a musical adventure which can last for years.
South Bank Centre, London SE1 (020-7921 0953; www.rfh.org.uk/education) Gamelan Taster Days from 10 January, beginners' courses from 15 January