Anyone who, as a kid at summer camp, learned to sing "Row, Row, Row Your Boat," "Three Blind Mice" and "Fre`res Jacques" all together knows what a "Quodlibet" is. It was a favorite form of musical joke in the 15th and 16th centuries in which a number of popular songs were superimposed, and frequently the superimposition of texts was carefully calculated for suggestive implications. Of course, to get the joke, one had to be familiar with the songs in the first place.

Last night at the Tawes Recital Hall, the University of Maryland's early music ensemble, the Collegium Musicum, built a program around one of Loyset Compere's most sophisticated Quodlibets, "Au Travail Suis," and settings of six of the songs that Compere wove together in this intricate musical puzzle. The settings were by the finest composers of the late 15th and early 16th centuries -- Dufay, Agricola, Josquin and Compere himself -- but in this performance it was the music of Dufay that stood out, even in this august company.

The music was performed on an assortment of soft instruments, recorders, viols, lutes and crumhorns, and on a group of loud shawms and a sackbut with a sound that could have peeled paint off a wall. Mezzo-soprano Elizabeth Barber, who seemed particularly attuned to the two Dufay songs, had no success in projecting the texts, but tenor Robert Petillo handled his small assignment with distinction.