What is the standard of review for a waiver?

"... [F]airness dictates that before accepting silence or acquiescence in sentencing by a different judge as a waiver, the court must satisfy itself from the record that defendant knew he had the right to be sentenced by the same judge who took his plea. The court cannot reasonably assume or speculate that the defendant had the requisite knowledge of his Arbuckle rights even if represented by an attorney." (People v. Rosaia (1984) 157 Cal.App.3d 832, 840, 203 Cal.Rptr. 856.)

The recent case of People v. Rosaia, supra, 157 Cal.App.3d 832, 203 Cal.Rptr. 856, is particularly instructive as to the appropriate standard of review of the facts in this case concerning an Arbuckle waiver: