As the theme for their Christmas celebration this year, The Sixteen chose different settings of O Magnum Mysterium, the gregorian chant intoned at Christmas Day Matins. All the more evocative for interweaving 20th-century composers’ reflections on the nativity, as well as Will Todd’s 21st-century My Lord Has Come, this was a typical Harry Christophers programme, simply done but rich in sonority and associations.

In Palestrina’s O Magnum Mysterium, Christophers created a flow which managed to be at once seamless and yet perfectly articulated, with first the sense of awe felt by the shepherds and then their jubilation in the Alleluias. By way of complement, the ensemble also sang the Kyrie and Gloria from Palestrina’s mass, of the same title, incorporating material from the motet into the new fabric. Victoria’s Matins text differs slightly, emphasised by the Sixteen with an almost ecstatic glow at the words O Beata Virgo and then in the extended Alleluia. Morten Lauridsen’s contemporary melismatic setting contrasted well, while the changing rhythmic pulse in Charles Ives’s A Christmas Carol connected neatly back to Palestrina.

More Palestrina added a further reinforcing thread: his O Solis Ortu Cardine, and the Magnificat whose alternation of plainchant with polyphonic settings achieved a graceful beauty. And with a final division of the Sixteen’s voices into three sections for their encore, Michael Praetorius’s Quem Pastores Laudavere, came changing colours and an aura of serenity.

• At Usher Hall, Edinburgh (0131-228 1155) on 9 December and Royal Festival Hall, London (0844-875 0073) on 12 December.