To say composer Martin Iddon, the Head of School and Professor of Music and Aesthetics at the University of Leeds, writes challenging music would be to use a cliché to achieve only an understatement. The five works on his pneuma are formal (well-formed) and complex pieces for small ensembles — with one piano solo — that seem designed to test the limits of the players. The string trio Danaë, for example, requires the musicians to play with a bow held in each hand and to play without use of the fingerboard.

That is just process, however, whereas what's important is the product. Iddon's music is also softly beautiful and very visceral, nearly tangible. The pieces proceed with a deep inner logic, wonderful detail and a gorgeous (slow) pace.

The disc opens with pneuma.sax, performed by Trio Atem, a British ensemble with the unusual instrumentation of flute, cello and voice. The prolonged tones serve as a nice introduction to the set without giving away everything that's in store. head down among the stems and bells is a focused piano study which uses amplification to bring out the mechanical knocks and plops of the instrument. That's followed by pneuma.kharis which — like the opening pneuma makes use of voice and prolonged tones, this time for bass clarinet, baritone voice, trumpet and trombone, played by the New York City ensemble loadbang. Danaë, then, harkens back to the piano solo in its magnification of "extraneous" instrumental sounds.

The final piece on the disc, hamadryads, may be the most exciting as well. Performed by the five members of the exceptional New York vocal ensemble ekmeles, the piece again works primarily in prolonged tones, but of the set best shows Iddon's talents for orchestration; the arrangement of the voices (soprano, mezzo-soprano, tenor, baritone, bass) and glass harmonica (wine glasses played by each of the singers) is engaging and slightly haunting.

This is heady music to be sure and there is much to be said about the inspirations Iddon found in Greek mythology and early music (an interview with the composer can be found at Another Timbre's site http://www.anothertimbre.com/pneuma.html). But such knowledge isn't prerequisite. pneuma's 71 minutes are simply — and complexly — wonderful.