At 8 p.m. last Saturday, in a pitch-black St. Ignatius Church, an audience of some 1,300 people sat motionless in the dark. What kept us that way was was 12 male voices, unaccompanied by anything but candlelight and including one astonishing soprano, singing 15th-century plainsong. I couldn't get a photo, of course, so the above shot (of Chanticleer rehearsing before the show) will have to do. There's something about this music that made me think, Why bother with anything else that's been composed in the last, oh, six hundred years? Though I changed my mind when the SF-based group wound up its performance with a medley of Christmas spirituals arranged by its artistic advisor (and former music director) Joseph Jennings. You can catch a repeat performance this Saturday—same place, same time.