That's perhaps the origin of "Kurzwellen" (1968), a piece in which the musicians have to operate portable radios, dialing in splatches of voice and melody, and then play along with them. The metaphor of the radio comes back time and again. In "Hymnen" (1966-69) the national anthems of the world morph into one another, just like surfing on the shortwave. Instruments are tweaked to sound exactly like a receiver tuned just off the station ("Mixtur" and "Mantra"). It sometimes seems like he's trawling the ether, looking for messages from the other side.

When listening to "Gesang der Jünglinge" (1956), you have to think that he has found one. Renowned composer Luciano Berio describes it as "the first great piece of electronic music," and it still knocks your socks off the first time you hear it. Against a backdrop of unearthly electronic sounds, the voice of a young boy comes across clearly and as uncannily as "an apple found on the moon," as Stockhausen put it at the time.

It's unlikely that anything quite like it could ever be made now -- the organic sound comes from impossibly fiddly tape manipulation that was madly labor-intensive. Experimentally splicing together tape at a length of 76.2 cm per second, for a 14-minute piece -- that's a lot of hard graft!

But that was all in the 1950s. As the clock rolled over to the '60s, it was time for him to mutate again. The Third Stockhausen ran off to join the circus.

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In New York, high modernism had dissolved into the perpetual performance art party. With his background in magical cabaret, Stockhausen fit right in, not so much composing as staging happenings for avant-gardistas like the Fluxus crew, who were more committed to goofy surrealist antics than to making music for the ages. One of them was pioneering video artist Nam June Paik (Stockhausen described him as "going berserk during my theater piece"), who would drink from his shoe, bathe in red paint and hurl glop at the audience while Stockhausen accompanied him at the piano. Another was painter and socialite Mary Bauermeister, who was to become his second wife and mother of one of his sons, Simon. (With his first wife, Doris, he had an additional son, Markus, and a daughter, Majella.)

This swinging Stockhausen was as schizophrenic as his times. On the left-hand path, he was making strange theatrical enchantments, which only linger in the program notes that remain. On the right-hand path, he was devising fresh ways of composing. Notation was out, weird instructions were in. Making classical musicians improvise is a tricky business. Usually, the orchestra will just vamp feebly until it gets back to the firm ground of the score. In Stockhausen's compositions from 1960 to 1975, the way the musicians interpret their instructions is the firm ground of the score, but his ideas weren't to reach their apotheosis until he went through a massive crisis, becoming the Fourth Stockhausen into the bargain.

When Stockhausen married Bauermeister in 1967, it was a splendid and joyous occasion on a boat in Sausalito, a picturesque bohemian stronghold located a few miles north of San Francisco -- but anyone could have seen it was a marriage of desperation. They broke up inside of a year. Depressed and on the verge of what a normal person might call a nervous breakdown, Stockhausen holed up in Paris and resolved to starve himself until either Bauermeister came back to him or he dropped dead, and pretty much either would do. It was May 1968, and while Paris rioted and invented situationist politics, Stockhausen discovered a book of Indian philosophy that a fan had slipped in his pocket.

After four days of misery and starvation, and with nothing but the words of Sri Aurobindo to sustain him, he walked over to the piano and struck the keys. In that heightened moment of consciousness, he hit upon one of the great works of all time, "Auf den sieben Tagen" ("From the Seven Days"). It seems like nothing much on the surface. No notes, no musical instructions, no great reorganizations of time and space, just a collection of spare texts, but, for Stockhausen, he had penetrated the spiritual heart of the universe.

The Fourth (and definitive) Stockhausen emerged from the chrysalis. By turns showman and shaman, he visited the world's sacred places to assemble a bricolage spirituality, spoke wherever he could find an audience and -- taking inspiration from his San Francisco days -- formed a band, which played what he called "intuitive music," based on the inspirational principles he had discovered.

The sleeve notes to "Aus den sieben Tagen" reveal that the command codes of the cosmos are remarkably simple:

Play a sound/Play it for so long/until you feel/that you should stop/ ... or Play a vibration in the rhythm of dreaming/and slowly transform it/into the rhythm of the universe.

Ah, those golden days of the Summer of Love! But if it sounds dippy to the modern mind, in practice it became as intense and rigorous an experience as sitting zazen for a week.

Or for over half a year, as it turned out. The band took center stage at Expo 70 in Osaka, Japan, where Stockhausen installed it to play his music for five-and-a-half hours solid every day for 183 days. Needless to say, the band broke up and, by 1971, the ride was over.

By the '70s, Stockhausen's work had escaped from its classical cradle. The big ideas laid the groundwork for improvisers as varied as Cecil Taylor, German art rockers Can and the electric period Miles Davis. The tools and techniques made way for the textures and humor of Kraftwerk and all the electronica that followed. And everybody now thinks that interacting with your media is standard operating procedure. So what do you do when you win the cultural war? You go home and take a rest.

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