As part of its Sunday afternoon concert at the Isabella Stewart Gardner Museum, the vocal quartet Anonymous 4 programmed a three-part motet from the 13th-century Montpellier Codex. The piece is odd. The lowest voice sings a snippet of sacred plainchant, slowed down to a glacial drone. The middle voice’s fancy turns to thoughts of more worldly devotion, pleading with a “dark-haired lady’’ for “your aid, your love, your comfort.’’
Meanwhile, the highest voice sings its own lament: “Love unfairly makes me suffer grief.’’ That all this was layered into music suitable for the cathedral - indeed, the group had already sung a similar motet, its words prudently rewritten to suit cloistered nuns - was part of the cross-pollinating, pleasantly enigmatic point.
Anonymous 4 - Ruth Cunningham, Marsha Genensky, Susan Hellauer, and Jacqueline Horner-Kwiatek - charms by preserving something of the past’s sheer foreignness. Celebrating its 25th season, the quartet featured at least one selection from each of its many recordings, a testament to its duly documented musical archeology. In performance, they don’t sound quite like anyone else. Their intonation is pure, but unlike many early-music groups, their voices remain distinct, each individual timbre is identifiable, even in unison chant. (The concert provided another acoustic datum for the Gardner’s new Calderwood Hall, which, from the floor seats, seemed somewhat dry for choral singing.)
The ensemble’s curiosity ranges wide, a millennium’s worth of repertoire. But no matter the style, the group has a knack for bringing out music’s ritual, comforting in its formality while intriguing in its mystery. In the medieval Hungarian New Year’s carol “Novus annus adiit,’’ steady declamation eased into far-flung melisma with a preternatural, purposeful calm. Hildegard of Bingen’s “O rubor sanguinis’’ pushed even further, a stately procession beyond words, the ornate melody unraveling the thread of the text.
Newer works took advantage of the quartet’s way with the limpid friction of harmonic clashes. David Lang’s 2011 “the wood and the vine’’ set a translation of Marie de France’s Tristan-themed “Chevrefoil’’ as a moody, circling paradigm of bittersweet love; Richard Einhorn’s 2001 “The Scientist’’ worked Galileo’s famous “Eppur si muove’’ declaration into lapping, looping waves.
The concert closed with a pair of 19th-century American shape-note hymns, unassuming sturdiness that might seem a long way from the intricacies of medieval courtly love. But here, too, the group’s genial prowess was both inviting and mysterious. Anonymous 4’s serene resolve nevertheless hints at secret joy.Matthew Guerrieri can be reached at firstname.lastname@example.org.