Missa Prolationum: Agnus Dei I by Johannes Ockeghem (1410 - 1497)

The Missa Prolationum is famous because the entire thing is an example of what is known as a prolation canon.  This means that the accompanying voices to the main melody are all imitations of that melody but are imitating it at different speeds (prolation = speed).  It is a very beautiful piece, performed by the Hilliard Ensemble in the recording I found.  I did find a score of this music and have attempted to see if I could trace the melody line through each different part.  It is kind of hard without printing it out and highlighting each entrance.  The idea of writing a prolation canon sounds like a very difficult challenge, which makes me want to give it a try at some point.  The Hilliard Ensemble always perform these pieces so well.  This piece begins with a nice duet and then expands to four voices after the first phrase.  I think I will try and look up the rest of the mass when I have some spare time to just listen to music.