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A resounding amen to Trio Mediaeval

Trio Mediaeval is (from left) Anna Maria Friman, Torunn Ostrem Ossum, and Linn Andrea Fuglseth. (CF Wesenberg)

CAMBRIDGE -- In their concert on Friday night, the Scandinavian women of Trio Mediaeval were their own a cappella amen corner. At the close of the chordal "Gloria" from the 14th-century compilation "Messe de Tournai, " the final "Amen" suddenly took playful flight, the "ah" vowel bouncing back and forth among the three singers. The "Credo" from the same Mass proclaimed its final "Amen" with stately fanfares; a 13th-century French "Veni Creator Spiritus" set the word with swinging rhythms that gave way to ambiguous, shadowed harmonies, a cloud passing across the sun.

The all-sacred vocal program interspersed the multiauthored Mass with similarly anonymous Italian devotional songs and two more formal works by the early French master Perotin; in moments like those "Amens," one could feel the composers playing with nascent Western polyphony like kids with a new toy.

The contrast between the Perotin pieces was most telling. "Beata Viscera, " a haunting meditation on the Virgin Mary, stood out from the surrounding music on the strength of its austere, elegantly assembled monophonic line. "Dum sigillum" is far more exuberant, a two-part contrapuntal discourse on the immaculate conception of Jesus, the Divine planting its kiss on human nature. "Marvelous kisses indeed," the text slyly remarks, "that have the power to bear fruit without the coupling of flesh." Perotin turns almost every word into its own fantasia, gleefully extending each "oo" vowel into dancing cadenzas, leaving the singers' lips almost permanently puckered in osculation.

The trio -- Anna Maria Friman, Linn Andrea Fuglseth, and Torunn Ostrem Ossum -- have breathtaking purity of intonation along with their all-but-vibratoless tone. Harmonies course with flowing exactness; unisons are flat-out uncanny.

Viscerally exciting sounds were few: The group opted more for shades of delicacy, rounding off phrases with a jeweler's precision, letting their timbre gently ride the church's reverberation rather than cutting through it. There were moments that could have used more bite, but the overall beauty was exceptional in its consistency. A contemporary encore, Ivan Moody's 1998 "Words of the Angel," made an appropriate connection with the rest of the evening's composers, who reveled in their own shock of the new.