THANKS to the work of organisations like NYCoS and its use of the Kodaly method of teaching, many young Scots can now read music. But the dark art of free improvisation is still a mystery to many, even within the ranks of professional musicians.

Trombonist George Lewis, a member of Chicago's Association for the Advancement of Creative Musicians for more than four decades, is one of the world's foremost practioners, and this recording with the Glasgow collective, one of the world's few big bands dedicated to collective improvisation, documents a collaboration that dates back to 2003.

This 2012 recording of a Lewis score for the band, graphic rather than notated and broadly a grid of instructions, captures well exactly what all that means, and its rich palette of plucked, blown, beaten, and sung noises often rises above the suspicion that such music is more fun to play than it is to listen to.

The notes with the disc talk of the need for the players to demonstrate social rather than technical virtuosity, and the Lewis pieces certainly demonstrate a discipline in the art that the completely free improvisation that follows lacks, for all its collective climax at the 16 minute point.