Rondellus
Medieval technique of strict voice exchange, in which parts trade their phrases in rotation.
What it means
The rondellus is a medieval technique, cultivated chiefly in England, in which two or three voices sing the same melodic phrases but exchange them among themselves in rotation: what the top voice sings first is then taken over by another voice, while the first voice moves on to the next phrase.
Musical use
This voice-exchange technique produces a dense, canon-like sound without the voices needing to enter at a strict time delay as in a canon. The rondellus appears chiefly in English polyphony of the 13th century, for instance in connection with the famous round "Sumer is icumen in". The rondellus is distinct from the canon, in which the same melody enters at a time delay, whereas in the rondellus the voices trade their different phrases simultaneously but in rotation.
Performance practice
When singing or playing a rondellus, shape each phrase you take over in exactly the same way as the previous voice did, so the melody's rotating flow between the parts remains audible.