Does a district judge have to consider the credibility of the central witnesses before making an order based on the findings of a magistrate?

Had the district judge rejected the magistrate's conclusions regarding the credibility of the central witnesses without hearing live testimony from those witnesses, troubling questions of constitutional due process would have been raised. ... When the constitutional rights of a criminal defendant are involved, "the district judge should not enter an order inconsistent with the credibility choices made by the magistrate without personally hearing the live testimony of the witnesses whose testimony is determinative."

Id. at 19-20 (quoting Louis v. Blackburn, 630 F.2d 1105, 1109 (5th Cir. 1980)).