CLASSICAL MUSIC Planet Tree Music Festival Conway Hall & Steiner Theatre, London

The week-long Planet Tree Music Festival sought to celebrate "contemporary music which does not deal dominantly with the shadow side of expression". You don't have to be a convinced modernist to feel that some composers these days are merely jumping on the "faith-minimalist" bandwagon to gain easy fame. Yet musicians in every era have been concerned with spiritual values. And the majority of those involved with this festival are seriously intentioned; some of them - including its indefatigable director, Lawrence Ball - have been addressing the role of music in meditation and healing for many years. Nor did Planet Tree confine itself to composers who make such specific connections with matters of the spirit.

Ball also valiantly attempted to broaden the audience for such music by collaborating with Greenpeace and Friends of the Earth. In return for presentations at the start of most of the events, these organisations promised financial and promotional help. For a variety of reasons, however, this collaboration didn't produce the hoped-for audiences.

Indeed on Sunday, barely a dozen of us gathered at the Steiner Theatre to hear works by the reclusive, 73-year-old French "minimalist", Jean Catoire. The endlessly revolving triads of his chamber, vocal and organ compositions had a hard job conveying an appropriately contemplative mood, even when performed with the dedication of musicians such as James D'Angelo, a fervent champion of the composer. In a darkened church late at night, the effect just might have been revelatory.

Other almost equally ascetic music worked much better. John Tilbury's collection of the 21 piano pieces by Howard Skempton, which focus almost entirely on slow chord sequences, proved a genuinely uplifting experience. And pieces by Ball and D'Angelo themselves - including the former's delightful Waterfall and Brightness - demonstrated skills usually lacking in unreconstructed tonal composers, and imaginative and entertaining ways of elaborating simple materials.

The highlights of the Planet Tree Festival, however, were the two concerts by Terry Riley. An illustrated lecture also offered tapes of some of this American minimalist's determinedly unminimalist recent compositions. But the real Riley is a born improviser. Whether playing the piano or singing in the Indian style of his late guru, Pandit Pran Nath, Riley simply oozes ideas and an effortless musicianship placed totally at the service of music as a truly spiritual art. The extended Night Music demonstrated a masterly control of structure and timing. His improvisations are rooted in jazz as well as Indian traditions; Riley has spent a lifetime immersed in both, and it shows. But most notable is how he transforms everything he touches, making one hear the most hackneyed gesture or even simple interval in new ways. John Whiting's ambisonic sound system enhanced the moving effect of this music in Conway Hall. While attendances were better, a performer of Riley's calibre should be heard by capacity audiences. It's good to learn that he will probably be in Britain again soon.