"In Nomine" is one of the masterpiece of the English ancient music and one of the most difficult and intricate pieces to play of this period.
This compositional and virtuosic tour de force by John Bull (1562-1628) compares with Tallis's Felix Namque... in its extended use of a plainsong cantus firmus. However Bull does something which was unique at the time by making every third bar 3 beats within an otherwise 4 beat piece. This has has the effect of making a cycle of 11 beats. Nobody before Stravinsky ever experimented with irregular bars, certainly not in the 16thC. But it's not a stunt, it's also a wonderful piece. The piece comes from the Fitzwilliam Virginal Book.
http://www.youtube.com/watch?v=badMOWcxpvY
http://www.marcolomuscio.com