Pierre Boulez, leading composer of the post-war generation and later a powerful and innovative conductor, is now the head of an extraordinary experimental studio in Paris. This huge underground music laboratory was built especially for Boulez beneath the Pompidou Centre. Here, for the past-seven years, accompanied by computers and music assistants, he has been developing his most ambitious work to date - 'Répons'. It had a huge success at last year's Proms. In tonight's film he shares his ideas and methods of working, introduces extracts from 'Répons', and describes his enthusiasm for opening a window on a new world of sound.