Orlando Chamber Choir / Wickham, St John's, Smith Square, London

It is a time-honoured practice among composers setting sacred texts to show their reverence by reverting to the supposed gravity of earlier styles. Already, back in 1610, Monteverdi felt it politic to model his Missa in illo tempore on the severe contrapuntal style of a motet by the Flemish composer Nicolas Gombert, composed some 80 years before. And Stravinsky's Mass of 1948 - written, the composer claimed, in reaction to the "rococo-operatic sweets of sin" of some Mozart masses he had found in a Los Angeles bookstore - evokes the aura of half a millennium earlier.

But the work evokes it, of course, by Stravinsky's usual methods of musical allusion and collage to create an "archaic" style that never was - its choral litanies glowingly enhanced by the clotted harmonies and creaking progressions of a double wind quintet. Its dense textures require careful balancing and crisp articulation, however, and these were not always forthcoming in its performance here.

Perhaps because, at 37 voices, the Orlando Chamber Choir is rather large for this piece, and perhaps because the conductor Edward Wickham's beat was too soft-edged always to secure exactitude from the Royal Academy woodwind and brass of the Orlando Players, the performance, though deeply felt, remained a little fuzzy. True, Wickham's decision to interpolate two of Stravinsky's brief unaccompanied settings in his more Russian Orthodox style - the "Ave Maria" and "Pater Noster" - either side of the Credo offered contrast. But this was rather neutralised by his assigning of Stravinsky's solo lines in the Gloria and Sanctus to whole sections of the choir.

Textural definition remained a problem in the second half, in which the Monteverdi Missa was preceded by Gombert's intricately woven motet "In Illo Tempore", upon which it is based. And here the interpolation of two Monteverdi motets in his more chordal, declamatory later style - "Christe, Adoremus Te" and "Adoramus Te, Christe" - came as a positive relief. For, aside from a four-part section in the Credo, the Missa itself is written throughout in relentlessly florid six-part texture, except at the end where it goes into seven. And between the relative clarity of the soprano and bass lines, it was not always easy to hear what the inner voices of the choir were up to.

Yet, given these singers' patent commitment, the performance could hardly fail, so gloriously fervent and resourceful is Monteverdi's writing, with its closely worked points of imitation mounting and tumbling in waves of sound. To those of his contemporaries who complained that his more modernistic experiments were debasing the musical currency, this was his overwhelming reaffirmation of the olden style.