Blue Heron is a touring troupe devoted to the performance of medieval music. They appeared at Brandeis University in Waltham as part of a two-day workshop on late medieval music. The evening’s program was dedicated to French music of the 14th Century, known as the Ars Nova period, the last era of medieval art before the Renaissance. Among the selections played was a piece only recently discovered. We were told that we were the first audience to hear it performed in 700 years!