Fans of early minimalism - the music that came out of New York in the late 1960s and early 1970s - have had a good week. Just a few days after the London Sinfonietta's programme of pieces by Steve Reich in the Hayward Gallery, the main work in the concert that the ensemble Icebreaker gave as part of the IF:06 festival was another minimalist classic from the same era, Philip Glass's hour-long Music With Changing Parts.

Glass has gone on to be so prolific that the pieces he wrote in the 1970s for his own ensemble, genuinely groundbreaking though they were, are rarely played now. In his later music, the techniques on which they were based have become just a means to an end rather than the end in themselves.

Music With Changing Parts, first performed in 1970, is one of the richest of those pieces in terms of texture. It's built out of a collection of 80 musical patterns played in sequence by the ensemble in rhythmic unison; as the instrumentalists move from one figure to the next, however, they are allowed to vary the harmonies and to emphasise the sustained pitches which provide the piece with its own kind of tonal architecture. Here the amplification used did that structure no favours; the 13 instrumentalists, with keyboards and saxophones predominating, blended into a muddy sound that deprived the interlocking patterns of their impact.

It followed a first half that had been equally frustrating. The first work in the advertised programme was omitted without explanation, and the three short pieces that actually began the concert - by Conlon Nancarrow (an arrangement of one of his player-piano studies), Frank Zappa and Erik Bunger were also neutered by the glaze of the amplification. Two pieces by Joe Hughes at least showed a talent for vivid musical ideas, and there were also some visceral sonorities in Gallows Hill, by John Godfrey, one of Icebreaker's founders, though, like the rest of the concert, it seemed more about style than real musical substance.