coulda been a programming mistake. someone made a comment that in the coding address, the Chanting Volume is the next letter/number from what all the other ducks have--magic repel
Also, it may simply be an attempt by the creators to say that Sgt. Joe has a very liud voice. The skill's translation is not quite right--it should have just been Vocal Volume or something. "Chanting" makes it sound a tad strange, because you're supposed to be singing.