The music of the American minimalist composer Philip Glass goes on and on and on. Typically, it suggests circles within circles and wheels within wheels, with endlessly repeated motifs swirling like water in ever- narrowing rhythmic spirals towards the ultimate plug-hole of a thematic resolution.
Not, on the face of it, the ideal rhythms for film. Yet Glass has just composed the music for both Sean Mathias's Bent, released last week, and Martin Scorsese's life of the Dalai Lama, Kundun, to be released next month.
Indeed, Glass has encompassed some of the most interesting movies of the past 20 years, with the memory of the music often lingering longer than the films themselves. There's Godfrey Reggio's Koyaanisqatsi, with its famous time-lapse image of an impossibly large moon waxing over Manhattan; the steadily mounting climax of Paul Schrader's extraordinary Mishima, A Life in Four Chapters; and the uneasy tension of Errol Morris's Thin Blue Line.
Does the music accompany the film or vice versa? The question conceals the fact that composing for film is not one of his favourite pastimes. "It isn't attractive for me at all," he says on the telephone from Brazil, where he is sheltering from New York's winter while working on a Millennium Symphony for next year's Salzburg Festival. "It's my least favourite, because when the film is done I can't go back and re-write it, but with an opera I can. Film is a director's medium, while the opera is a composer's house."
None the less, he talks of his most recent ventures favourably. Indeed, Glass is still excited at the memory of working with Mick Jagger, who appears as a drag artist in Bent, and for whom he wrote a song.
"One of the great pleasures for me was writing the song for Jagger," he says. "I went to London and we spent three or four hours on it, and by the time we had finished, it sounded like he had written it himself.
"I didn't really know his work and Sean Mathias had said we needed this song, but at that point it wasn't certain that Mick would play the part. Sean and I had talked about Cabaret and Kurt Weill and we were referencing a certain historical kind of music. Then I got the text for the lyrics from the writer, Martin Sherman, Jagger was confirmed for the role, and we began to do it."
The song is one of the most effective moments in the film.
The commission to compose for Scorsese's Kundun, however, was a much more personal project. Glass is a follower of Buddhism, and last week Martin Scorsese, in his lecture at the NFT, said that although he wasn't aware of Glass's music when he first began preparing the film, he came upon the composer at some of the expatriate Tibetan festivals he visited as part of his research.
"This was quite a different thing," Glass says of his role on Kundun. "I spent 18 months working on it and I composed music as Scorsese was editing, and he spent eight months editing.
"With Marty, I could work on the scenario like working with the libretto in an opera, but in the editing stage things got rough. I had to re-write and then he would re-edit and I had to re-write again. There were some scenes he re-edited seven or eight times.
"The night before the final mix was due to be recorded I got a phone call from his editor, Thelma Schoonmaker, and she said: 'Guess what? We re-edited the scene again today.' I said, 'But we're recording tomorrow!', and I had to go off and change the score once more."
Eventually, there came a moment when the producer just said "This is it!" and the film was dragged screaming from his hands.
"Working with Marty, I began to learn about film in a way I'd never seen before. When we started, he had envisaged the whole film before the camera was even there. I would say he was the least compromising director I have ever worked with. People say it's a Disney film, but I never worked with Disney, I worked with Marty."
The aesthetics of Glass's own music were formed partly as a response to the time he spent in India in the mid-Sixties, and he already had direct experience of working with the Tibetan community. "When I came back to New York from India in 1967 I began to work with Tibetans who were trickling into the US as exiles in various community and educational projects," Glass says. "The subject of the film is a tragic one: the systematic destruction of a culture. Marty responded to this, and his goal was to make the world aware of what was happening to Tibet. In Brazil, you know, the rainforest is threatened, but Tibet is like a human ecology that is being destroyed as we speak."
Glass's latest project, and probably the closest to his heart, is also related to film, but with a very special difference. The project Monsters of Grace - a collaboration with the theatre director Robert Wilson, with whom Glass worked on the legendary opera Einstein On the Beach 20 years ago, and which opens the Barbican's refurbished theatre in May - is a film in which the actors are all "synthespians", computer-generated figures who have been painstakingly scanned into life by the technicians of Silicon Graphics Inc, the market leader in film special effects.
"It's a music-theatre work in which the images consist of projected 3- D images based on the computer realisation of a story of Bob's," Glass says. "The text is based on the verses of the 13th-century Sufi poet Rumi; there's 13 parts and the sequence of images is based on themes that recur, story-boarded by Bob and then translated into 35mm images that you view through 3D glasses. It's a piece of about 70 minutes in length, without intermission. The attraction is in combining the technology with live performance, and that is the power of the thing.
"I don't think it would interest me if the music were recorded too. I'm not ready to be a virtual composer."
Even with the realisation of the project - which has been in preparation for four years - in sight, Glass is still a little pessimistic. "You have all of the problems of a film without any of the benefits," he says. "With a movie you can have 2,000 prints made and it can play in many places simultaneously. This piece is hand-crafted and it can only be shown once a night."
The piece - which promises to be the theatrical event of the year - is further evidence of Glass's place within a powerful tradition of Surrealism in American art. "Maybe we've taken things that Cocteau would have used," he says. "It kind of comes out of that world, but you can't say we've overtaken him. Just look at Orphee and all those effects that Cocteau did with like a dollar and 35 cents. We're spending quite a lot more and still lagging behind him!
"Bob Wilson and I agreed to share the stage. It's a kind of extreme formal courtesy that allows us to work together, producing five or six pieces over 20 years."
The spectacle of the Barbican audience in their 3-D glasses, looking like that famous old photo by Weegee, will surely be a sight not to be missed, and, come May, the hottest high-art ticket in town.
'Bent' is on general release. 'Kundun' is released next month, with the soundtrack album available on Nonesuch Records from 3 April. 'Monsters of Grace' plays at the Barbican from 19-23 May; booking on 0171-638 8891.
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