Violinist Irvine Arditti, pianist Claude Helffer, and the Spectrum ensemble conducted by Guy Protheroe produce consummate performances of the Greek avant-gardist's unwieldy chamber music. If you're familiar with Xenakis's career you'll know he was trained in mathematics and enjoyed a successful career as an architect. Such background might prepare you for the music's preoccupation with line, volume, and form in an unusually abstract way, but it won't prepare you for its visceral, almost primitive power. On Akanthos, the singer Penelope Walmsley-Clark must cope with what is surely one of the most ridiculous soprano parts ever written.