by Blair Sanderson Judging by its intensely concentrated performance, clear layout, and stunning sound, this splendid recording seems the definitive rendition of Gérard Grisey's Les Espaces Acoustiques -- perhaps the clearest explication of the spectral school's theories and practices, but certainly one of that movement's most expansive works. Grisey, along with Tristan Murail, Roger Tessier, and Michaël Levinas, scientifically explored sound and acoustics in the 1970s and composed music of remarkable spatial depth, shimmering timbres, and dense textures based on natural overtones, the changing resonances of pitches in space, and the periodicity of events. Though this immense cycle was composed out of sequence, its progression from the 1976 Prologue for solo viola through movements for ensembles of ever-increasing size, to the massive Transitoires for full orchestra (1980-1981) clearly illustrates Grisey's methodology; and Les Espaces Acoustiques seems a step-by-step introduction into the difficulties and marvels of this new, analytical music, perhaps akin to the didactic works by Bach that introduced equal temperament. Violist Garth Knox, the ASKO Ensemble, and the WDR Sinfonieorchester Köln, conducted by Stefan Asbury, are all well-versed in this specialized idiom, and perform Grisey's magnum opus with a fascinating combination of grit and delicacy. Kairo's reproduction is absolutely superb; but beware of some piercing sonorities -- this is not music for the faint-hearted.