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).
In this example, the first 12 bars of the Agnus Dei II of the earlier of the two masses Josquin wrote based on the L'homme armé tune, each voice sings the same music, but at different speeds.
[1] Additionally, Larry Polansky has written numerous four-voice prolation canons whose melodies are permutations of a limited number of elements, and Mark Alburger, in Immortality from San Rafael News, directly maps a new melody into the framework of the aforementioned Josquin.
[citation needed] A particularly striking example of prolation canon occurs twice in the opening movement of Shostakovich's Symphony No.
A more recent example of a prolation canon in contemporary music is rindenmotette (2011) by Austrian composer Klaus Lang.