Hildegard von Bingen’s music is some of the best the Middle Ages has to offer, and Anonymous 4 is a fabulous performer of chant. On the antiphon “O rubor,” here, for instance, the phrases breathe just right, the blend is gorgeous, and Hildegard’s long, winding lines leap off the record. The album covers a lot of the Hildegard classics, but not in a rote or formulaic way — it has a sense of curation and definite artistic direction.