TO CATCH two works by contemporary American composers of different generations would seem to be reason enough to venture to Cirencester and hear for the first time the Cantores Chamber Choir, performing in St John the Baptist's, with its magnificent early- 15th-century tower and buttresses.

The two works are the exquisitely reflective Sure On This Shining Night by Morten Lauridsen, who is now in his seventies, and the somewhat exhaustingly jaunty, minimalist setting of St John of the Cross's poem "Dark Night of the Soul" by the Norwegian-born Ola Gjeilo, now 36.

Nothing, however, prepared me for the level of excellence I encountered. Directed by John Holloway, with crucial and varied keyboard support from John Wright, Cantores is without doubt one of the most meticulously rehearsed and magnificently refined ensembles I have heard in the past year.

Bach's funeral motet Der Geist hilft unser Schwachheit auf, one of his lesser known, unveiled some of the many details that place Cantores in the front rank. Their turnout (scarlet, black) is impeccable, as was their tuning, a well-maintained legato, and a finessed interplay that rendered Bach's counterpoint lucid, never clouded. This appeal to, and trust in, the Holy Spirit ("Sondern der Geist selbst vertritt") displayed the near-perfect shadings of the upper lines, soprano and alto, and the spirited engagement and sustaining of the basses; the expressive tenor line would prove itself later.

Most astonishing of all at the outset was the unconscious and unrehearsed period-like sound produced by the Cantores String Ensemble: this Bach really had twang.

Here, as indeed throughout the concert (including two marvellously expounded instrumental works by Boyce and Handel) - except perhaps in Monteverdi's Dixit Dominus, which felt uneasier and initially muddy - John Holloway's gift for hitting on just the right pace - right for the players, the singers, and for the work in question - yielded dividends galore. Where the music danced, it really did so, acquiring a joyous expressiveness. Where it growled, as in the same Monteverdi piece (grim lines from Psalm 110, "The Lord said unto my Lord"), it seethed and was vital: the violent, threatening ". . . im- plebit ruinas, conquassabit capita" was especially dramatic and convincing.

Gjeilo's "Dark Night of the Soul" was intended to exemplify the concert's theme, "The Power of the Spirit", text and music "imbued with medieval mystery". St John of the Cross's famous words ("One dark night, fired with love's urgent longings - ah, the sheer grace") certainly have that effect.

The performance, abetted by rich cantilenas from the lead violinist Peter Stacey, was excitable, agitated, even positively violent. What Gjeilo's setting does not allow, it seems, is balance or delicacy: there is no restraint, and simply too much going on. You could see the sopranos, for instance, were enunciating beautifully; yet St John's text was buried. It proved a loud, rumbustious thrumming, but, in the end, not much more.

One of the feathers in the cap of Cantores is the sheer number of choir members - in all parts - able to serve up solos not just competently, but stylishly and distinctively. Every one, without exception, proved memorable, and there were many. These solo offerings had personality, vocal colouring, rhythmic flair. It was like hearing the beautifully differentiated colours of a symphony (or chamber) orchestra. Paired sopranos ("quia respexit"; "dispersit") and sopranos or altos ("esurientes") in Monteverdi's Magnificat (not the 1610, but the late setting from his 1640 collec- tion Selva Morale e Spirituali) stood out, but there were so many more.

The Bach aside, two works stood out for me. One, not surprisingly, is Lauridsen's enchanting setting of a poem by the hugely influential, Pulitzer Prize-winning James Agee (1909-55), which might almost ("Sure on this shining night I weep for wonder. . .) be a modern descendant of St John's inspiring 16th-century verse. Here the tenors and basses were superlative, and a tenor descant to the ensuing tutti no less so (a soprano cantilena likewise). It was particularly magical with piano: splendidly restrained, atmospheric, and simply con- ceived, but never banal or naïve - in these hands, an obvious masterpiece.

This led on to 15 minutes of utterly thrilling Baroque. Francesco Cavalli (1602-76) a choir member of St Mark's, Venice, under Monteverdi in his teens, and himself appointed choirmaster a quarter of a century after his teacher's death, produced an eight-part Magnificat that is more than a match for his master. In some ways, it seems to anticipate, or usher in, the later high Baroque. The spirit of the dance prevails, vibrant and joyous.

There are exciting outburstsat "omnes generationes" and "in brachio suo": dynamic surges showing off the choir's dramatic power. At "Dispersit superbos", the music harks back to classic Monteverdian practice, the secunda prattica. The "sicut locutus" is more Cavallian - lighter, buoyant, delightful; and the doxology is a treat - joyous but artful. The elegance of the inner parts shone throughout. The enchanting outer lines spoke for themselves.