The name of this visiting ensemble evokes, from some, hushed tones of appreciation; from less familiar others, evocations of a shadowy political cabal or many-headed Whovian enemy. Were we workshopping a sci-fi baddie, we could do worse than an entity that communicates via one voice. And it is this precision outlining fulsome harmony that marks out The Sixteen for me as one of the world's finest choirs, proven tonight along with especially inventive and appropriate programming from conductor and founder Harry Christophers.

Exploring Christ Church Cathedral beforehand, I fortunately happen to meet original member and current Workshop Facilitator Sally Dunkley over a glass of wine in the north transept. Her researching and editing roles have made her an authority not only on early music, but on the 20th century and beyond - I'm promised "shivers" from Poulenc's Un soir de neige. I and many other listeners may have come to tonight for the Renaissance perfection of Palestrina, but it is the realisation of 20th century upstart Poulenc's writing that is the evening's revelation.

This year's Choral Pilgrimage tour is entitled 'The Olive Branch', and as well as including texts in search of peace both personal and international, the programme finds accord between two disparate composers. The most apparent common thread is their shared Catholic faith, but other echoes are discernable. We open with Poulenc's 'Salve Regina', its measured homophony showcasing The Sixteen's flawless dynamic balance and diction, and the composer's way with making well-judged dissonance send ripples across a still harmonic pond. Next flows the smooth polyphony from four centuries previously, in the form of lustrous biblical settings from Song of Songs and Job. The common device of setting the word "surge" ("arise") to ascending melodic runs is mirrored in Poulenc's following "vos fugam capietis" ("you will take flight") from his selection of motets, but this time the flight is an abandonment, sung about in bewildered ragtime stabs. These Quatre Motets also pick up Job's supplicatory mood, being 'pour un temps de pénitence', and are incredibly moving. Christophers' use of silence is key here: it punctuates lines about the crucified Jesus here, as he breathes his last; it separates verbal repetitions in the later soir de neige ("nous... nous na'vons pas de feu... pas de feu") illustrating winter's desiccating effect on the self-aware authorial voice; it delays applause until the vocalists' last reverberations have become imperceptible in this cathedral's vaulted space.

After an interval affording a circuit of the dimly lit quadrangle, the absence of silence elides a French folk song into the Palestrina 'Kyrie' it inspired. This perfect segue allows a monophonic text about fear of 'L'Homme Armé' to flow into a plea for God's mercy - touching thematic programming, which leads into material from Palestrina's mass of the same name. In both the 'Gloria' and 'Credo', mention of the Holy Spirit refreshes the rhythm and texture, and the choir's approach allows such variations appropriate subtlety ('Gloria') and impact ('Credo') - the technical challenges of their repertoire aside, their articulation is nigh impossible to fault.