Amazon.comThe 13th-century Tournai Mass (named for the city where its manuscript was preserved) is the oldest surviving polyphonic (i.e., for more than one voice) Mass cycle. The three voices move together from note to note; the harmonies are spare, with pungent dissonances often appearing just before the ends of phrases. Ensemble Organum has added chants proper to a Mass for the Virgin--the plainchant context makes the polyphony seem all the more striking. Marcel Pérès, the mad genius of medieval music, often applies vocal techniques from such places as Greece and Corsica to Western European chant--not always with convincing results; this is one of his least quirky recordings and is recommended for anyone interested in the Middle Ages. --Matthew Westphal