A brighter tone arrived with works about the Nativity itself, such as Jean Mouton's glowing "Nesciens mater" and Antoine Brumel's "Nato canunt omnia." The latter was as complex as Obrecht's piece, but its bold, joyous sounds clearly bespoke the wonder of the season. All of it was beautifully rendered by various permutations of Blue Heron singers under music director Scott Metcalfe's subtle yet precise direction.
There was an abrupt shift in color as the program traveled back to the 12th century. If the music of the first half was often a thick stew of shades and half tones, the older selections arrived in stark juxtapositions of black and white.
Much of the second half was devoted to two graduals by Perotin, one of medieval music's great innovators. In "Viderunt omnes" and "Sederunt principes," one voice sings a chant melody at a very slow tempo, while the others dance above it in repeated rhythms. Vast stretches of music unfold on a single syllable, a technique that at times threatens to obliterate the text and its message. Like a later French composer, Olivier Messiaen, Perotin forces listeners to enlarge their sense of musical time in order to fully appreciate his art.
Interspersed with the Perotin were two pieces discovered in a medieval Aquitaine church, in arrangements by the early-music group Sequentia. One, "Per partum virginis," was sung by three mezzo-sopranos; Pamela Dellal and Daniela Tosic intoned a chant melody over which Lydia Knutson wove florid, almost improvisatory melodies.
It is hard to imagine music more naked and exposed than this, a long way from the comforting warmth of more common seasonal offerings. Yet, in its own mysterious way, it was no less jubilant, no less promising of another season of joy.
