What is the burden of proving a defendant's confession?

prosecution has the burden of establishing by a preponderance of the evidence that a defendant's confession was voluntarily made.' [Citation.] 'Whether a confession was voluntary depends upon the totality of the circumstances.' [Citations.] 'On appeal, we conduct an independent review of the trial court's legal determination and rely upon the trial court's findings on disputed facts if supported by substantial evidence.' [Citation.] The facts surrounding an admission or confession are undisputed . . . making the issue subject to our independent review." (People v. Linton (2013) 56 Cal.4th 1146, 1176-1177.)