CLASSICAL Hillier Ensemble Wigmore Hall, London

Paul Hillier knows a lot about Arvo Part, supported by his authorship of a monograph on the composer and long-term commitment to the Estonian's music. The singer brought his American-based Theatre of Voices to the Wigmore Hall on Monday to deliver a programme of unfamiliar Part set in the rather jarring company of motets and hockets from 14th-century France, England and Italy. Hillier's concert notes endorsed the common view of Part as a living conduit to the Middle Ages, his music embracing "the aesthetics of Gregorian chant and medieval polyphony"; that embrace, however, seems short on passion for the clever-clever Ars subtilior repertoire.

The simplified organ hocket, the prolonged cantus firmi and parallel organum of Part's De Profundis sounded light years removed from the exuberant, death-defying In seculum hockets which opened the recital, recalling far more the sound world of Satie than of Senleches. The late 18th-century encore piece, Abraham Wood's austere setting of "Man that is born of woman", proved much closer in spirit and message to Part than, for example, the celebratory motets of Johannes Ciconia or the florid Italian song "Per larghi prate".

The hocket technique, a musical version of the three-legged race in which a melodic line is broken up and shared by two voices, served to show a composer's prowess and a performing group's daring. The Theatre of Voices were daring enough, yet sounded strained and reticent for much of the concert's first half, the edge no doubt removed from their work by a busy tour of Italy and an early morning flight to London. Here the "theatre" was supplied by a tired high tenor struggling with the cruel demands of the anonymous English motet Doleo super te / Absolon fili mi, while the group's pastel-coloured silk shirts offered a modest scenic diversion. Hillier's approach is clearly about unlocking the rich expressive content of his chosen repertoire and to articulate the dramatic and emotional connotations of words. But the ancient and modern works in this programme also cry out to be heard in a "smells and bells" setting, or at least to be given the benefit of atmospheric lighting: the Wigmore Hall offered neither.

Part's delicate, deeply religious music extracted the best from the Theatre of Voices, crowned in the Two Slavonic Psalms by the rock-steady, pure- sounding soprano of Ellen Hargis and elsewhere underpinned by Christopher Bowers-Broadbent, making the most of a chamber organ in place of the full box of whistles. The organ solos, two from the Faenza Codex, the other, Part's Trivium, showed the clearest links between the Estonian's so-called tintinnabuli style and medieval music, especially so in the hypnotic Faenza "Benedicamus".

The most recent Part on show, the Memento mori of 1995, proved even more spare and rarefied in style than his earlier Missa sillabica, almost a pastiche of 19th-century Orthodox chant settings without the indulgent harmonies, and infinitely more moving as a result. Theatre of Voices missed the emotional mark in their medieval repertoire as often as they found it in Part, stretched by the rhythmic complexities and "instrumental" devices of the hocket pieces and forced into exuberance only by Ciconia's irresistible work and the lascivious Italian motet Cum marteill incrudenda. Andrew Stewart