What is a judge's duty to control all proceedings at trial?

"[I]t is 'the duty of the judge to control all proceedings during the trial, and to limit the introduction of evidence and the argument of counsel to relevant and material matters, with a view to the expeditious and effective ascertainment of the truth regarding the matters involved.' However, 'a judge should be careful not to throw the weight of his judicial position into a case, either for or against the defendant.' [Citation.] [] Trial judges 'should be exceedingly discreet in what they say and do in the presence of a jury lest they seem to lean toward or lend their influence to one side or the other.' [Citation.] A trial court commits misconduct if it ' "persists in making discourteous and disparaging remarks to a defendant's counsel and witnesses and utters frequent comment from which the jury may plainly perceive that the testimony of the witnesses is not believed by the judge." ' [Citations.]" (People v. Sturm, supra, 37 Cal.4th at pp. 1237-1238.)

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