We take a brief look at the career of avant garde music's most influential figure — and report on a performance of his latest creation, "Donnerstag Aus Licht", at the Royal Opera House, Covent Garden.

One of the most spectacular concerts ever seen on an English stage. That's the reaction from someone who went to Covent Garden with very mixed feelings about the UK premiere season of Karlheinz Stockhausen's latest epic electronic opera — and it's no exaggeration.

A few facts. After a classical music-education in Cologne, Stockhausen composed several musique concrete pieces such as 'Etude', and his first two purely electronic pieces using sinewave oscillators were 'Elektronische Studien I and II', composed in 1953/4.

His best-known piece is probably 'Kontakte', which explores the points of contact between known and unknown sounds, the acoustic and the electronic. The piece's arrangement allows Stockhausen to play astonishing tricks with time and space. At one point, a high-pitched note whizzes down through the audio spectrum, dropping to sub-audio levels and turning into a slow, repeated clonk. In Stockhausen's music, pitch is interchangeable with time, and stereo placement is interchangeable with space.

The German's obsession with time persists to the present day, and some of his musical relationships take place over massive intervals. In fact, many of the facts and figures associated with his music are every bit as astonishing as the music itself.

By 1964, he was composing pieces such as 'Mixtur' for five simultaneous orchestras and six years later, the Expo '70 World Fair saw his music performed for five-and-a-half hours per day for 183 days, by a group of 20 musicians for over a million listeners.

In 1975 he composed 'Tierkreis' ('Zodiac'), twelve 'melodies on the star signs' in versions for high soprano, soprano, alto, tenor, baritone and bass voice, with chord instrument, chamber orchestra, clarinet and piano. Then came the massive 'Sirius' for orchestra, musicians, singers and synthesiser tape.

Gradually, it became clear Stockhousen was working towards something big with a capital B. In 1977, it began to take shape in the form of 'Der Jahreslauf' ('The Course of the Year'), the first piece to be performed from the massive 'Licht; Die Sieben Tage Der Woche' ('Light; The Seven Days of the Week').

What we have in 'Donnerstag' is the first full 'day' of an eventual total of seven. Composing one 'day' every four or five years, Stockhausen aims to finish the work around 2006. Asked if he is confident of being able to finish 'Licht', he replies: 'Why not? I will still be in an early part of my life then, I will only be 75 years old.'

Of late, Stockhausen's more outrageous claims have maintained for him an international reputation which eclipses that gained in his native Germany. Not unnaturally, he feels the German music establishment is dominated by conservative forces still opposed to experimental music. And it's understandable that Stockhausen's occasional claims to be controlled by intelligences from Sirius while he's composing don't go down too well.

Even taking all this into account, it would have been difficult to anticipate just how 'Donnerstag' would turn out to be on the London stage. Hackneyed it may be, but the term 'cosmic' is the only way I can describe the surrealistic majesty of Stockhausen's production.

It takes as its subject matter the early life of Michael, the Creator-Angel of the local Universe of which Earth is a part, and his subsequent journey round the world and return to Heaven.

Although the opera is in three Acts, there's also a 'Greeting' performed by brass players in the theatre foyer as the audience are entering, with a corresponding 'Farewell' after the show. More musically-trained members of the audience no doubt spotted portions of recurring themes in both these snippets, but as usual, the niceties of Stockhausen's radical 12-tone composition got past most of us.

Entering the main hall, I was a little surprised to find Stockhausen himself supervising the 'sound projection' from the centre of the auditorium.

You want some idea of scale? Well, the Royal Opera House generally uses a 24-channel Neve mixer, but this was only sufficient for the orchestra on the night in question, so the composer added a 36-channel Cadac to cope with the solo performers and backing tapes.

With the Neve acting as a pre-mixer under the ROH sound department's head, Eric Pressley, Stockhausen opened Act 1 by mixing in an eight-track tape playing an 'invisible choir' of male and female voices from the House's under-stage sound room.

Twenty-two ElectroVoice speakers were used for sound projection, two at either side of the stage and two 'flown' above it, with the other 16 dotted around the balcony stalls.

The concert's consistently outstanding sound quality was largely thanks to radio mics worn by the singers and instrumentalists, and over 40 other mics in the orchestra pit, on the stage, and on the side stages used for some of the larger instruments such as the giant tam-tam (gong).

What else is there to talk about? Ah yes; the plot.

Act 1 opens with a huge backdrop depicting a brick wall, used to back-project various shadow displays as Michael acts out his early life. Each of the main characters is represented by three performers — a singer, a dancer and a musician — and their interactions are backed up by a set of music-related gestures developed by Stockhausen for the piece 'Inori'.

The speakers have an especially large part to play in Act 2, which adds a 28-piece orchestra and, like I say, one of the most spectacular sets used on an English operatic age. A huge globe of scaffolding, some 25-feet across, holds the figure of Michael as he prepares for his journey around the world. This begins with a lurch as the globe starts to rotate around the stage, stopping at seven points symbolising Germany, New York, Japan, Bali, India, Central Africa and Jerusalem — a suggestively autobiographical catalogue of a few of Stockhausen's major influences.

Then the globe halts, rotates backwards, and finally comes to rest at the end of Michael's journey. He plays the triple formula of the 'Michael theme' before preparing for his return home.

All credit for Act 3 must go to Lighting Designer Chris Ellis. In the face of almost impossible odds, what he achieved was quite unexpected, utterly spectacular, and no doubt something of a shock to seasoned theatre-goers accustomed to The Barber Of Seville and Swan Lake.

Act 3 is set in Heaven - Stockhausen doesn't mess about with his settings — and throws in absolutely everything, including an eight-track invisible choir tape, a two-track tape of snippets from earlier scenes, 11 soloists, a 61-piece orchestra, and five choral groups on stage dressed in metallic space suits. A huge circular stage section is the centre of the action, but after the opening solos, this stands empty before starting to tilt upwards, in total silence, towards the audience.

Standing under the Mothership in Close Encounters must have been something like this. The theatre fills with smoke, hails of silver confetti fall, and a huge rainbow of light dominates the stage, and the stage section, now pointing directly at the audience, starts to glow with a hundred multi-coloured flashing arc lights.

And before the audience can regain normal vision, the centre stage section explodes with the brightness of a dozen white arc lights in a cell-like pattern, and the stage begins to fall back into place.

Gary Numan would have turned green with envy — though the music continued to baffle anyone who didn't have the benefit of the extensive libretto or a smattering of German. Michael's battle with the Devil was lost on many, but Stockhausen has both clear and complex theories on the relationships between music, energy, life and harmony, of which this battle is just a tiny part.

Drawing conclusions about a four-hour piece that comprises only one-seventh of a finished work is a dangerous thing. But it's fair to say 'Donnerstag' is a magnificent musical and theatrical achievement, even though it can be few people's idea of an easy night out.

Unlike Philip Glass, Stockhausen designs his own sets, choreography and gestures, and even when these appear simple, they're usually the outcome of complex spatial and numeric relationships. His music is still less than accessible, though the composer's daughter, Majella, does hint at jazz piano phrasings in the 'Examination' section of the first Act, and Suzanne Stephens (as the glamorous Moon-Eve) wrings some incredible textures from the Basset Horn, an unusual and demanding instrument.

Whether the whole of 'Light' will ever be performed is open to question; it'll be about 24 hours long when it's finished. But if the staging is anything like the Covent Garden production, I'd recommend seeing even the smallest part of the piece.

'Samstag' ('Saturday') is now finished, and uses one solo voice, ten solo instrumentalists, a stilt dancer, a solo dancer, a male chorus with electric organ, a symphonic band, a 26-piece brass orchestra — and two percussionists for the Greeting. 'Montag' ('Monday') is already under way, and there's no reason to suppose that it's any less spectacular.

I sometimes find myself wishing Stockhausen played up the electronic parts of his composition. His sons Michael and Simon, who both have parts in 'Donnerstag', accompanied their father in some recent Barbican concerts on Moog and Oberheim synthesisers, and both have been involved with electronics in jazz and rock bands.

But Stockhausen is classically-trained, can't afford a Fairlight (though he says he'd like one), and will continue to use electronics on an approximately equal footing with conventional instruments, sound-processing, tape collage, the human voice, choreography, mime, gesture, symbolism, surrealism, mysticism, and all the rest of it.

He's a compulsive innovator who works without compromise. Most of his audience can only sit and wonder.