Jane Alden raises her hands and cues members of her Collegium Musicum performance ensemble to intone the music. The sopranos and basses situated in Memorial Chapel’s choir loft allow their voices to resonate throughout the space. Alden cuts them off at measure 17. "Measure 17 is the apex because the cantus firmus is in the top voice. You need to sound like angels floating on the top with the chant,” Alden says during a Nov. 23 rehersal . “Let’s try this once more." The MUSC438 course, which explores vocal and instrumental repertories of the Medieval, Renaissance, and Baroque periods of European music history, is taught…