I can recall the first time I heard an example of the late-medieval multi-part liturgical canon. My first thought was: how can moderns believe that we listen to complicated music? Nothing can compare with this. If you haven't heard anything like this - and you probably will not in your parish - you will be amazed. The first example here is Josquin's Qui Habitat for 24 voices. The second example is Ockehem's Deo gratis for 36 voices! Both are 15th century compositions. Both bring into question all conventional notions of the course of artistic progress.