It sounds like an April Fools joke, but it isn't! This piece by the Renaissance composer Christopher Tye (c. 1505-c. 1572) is the last of a set of 21 instrumental pieces that share the same cantus firmus. They begin simply, and become increasing complex as they go along. In this, the final piece of the set, Tye puts the two upper voices in 3/4 time, and the three lower voices in 4/4 time. I imagine he amused (or perhaps frustrated) his friends with this.
You can listen to it here.