Mensuration canon

In music, a prolation canon or mensuration canon is a type of canon, a musical composition wherein the main melody is accompanied by one or more imitations of that melody in other voices. Not only do the voices sing or play the same melody, they do so at different speeds (or prolations, a mensuration term that dates to the medieval and Renaissance eras). Accompanying voices may enter either simultaneously or successively. Prolation canons are among the most difficult to write, and are relatively rare in the repertory, though they are most common in the early Renaissance and from the 20th century to the present.