Is a defendant's due process rights adequately protected when a district judge rejects a magistrate judge's proposed findings on credibility when those findings are dispositive and substitute the judge's own appraisal without seeing and hearing the defendant and witnesses whose credibility is in question?

QUESTION(S) PRESENTED Is a defendant's due process rights adequetly protected when a district judge rejects a magistrate judge's proposed findings on credibility when those findings are dispositive and substitute the judge's own appraisal; whithout seeing and hearing the defendant and witnesses whose credibility is in question?