Muggles' Guide to Harry Potter/Magic/Quietus

Overview
The Quietus charm is cast by a wizard, usually upon himself, to restore his voice to its normal volume after the use of the Sonorus charm.

Extended Description
The Quietus charm is first seen used by Ludo Bagman when he is called upon to commentate the Quidditch World Cup; when the game is finished, Ludo ends his earlier Sonorus charm by invoking Quietus.

Ludo uses this spell again after commentating the events in the Triwizard Tournament.