What demonstration of a defendant's consent is required to delegate jury selection (voir dire) to a magistrate judge under Peretz v. United States

“(a) Each United States magistrate judge serving under this chapter shall have within the district in which sessions are held by the court that appointed the magistrate judge, at other places where that court may function, and elsewhere as authorized by law— (1) all powers and duties conferred or imposed upon United States commissioners by law or by the Rules of Criminal Procedure for the United States District Courts; (2) the power to administer oaths and affirmations, issue orders pursuant to section 3142 of title 18 concerning release or …”