What is the burden of proving a defendant knowingly and voluntarily waived their Miranda right?

The prosecution has the burden of proving by a preponderance of the evidence that the defendant knowingly and voluntarily waived his Miranda rights. (People v. Whitson

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(1998) 17 Cal.4th 229, 248.) "Where the prosecution shows that a Miranda warning was given and that it was understood by the accused, an accused's uncoerced statement establishes an implied waiver of the right to remain silent." (Berghuis v. Thompkins (2010) 560 U.S. 370, 384 (Berghuis) [suspect implicitly waived his right to remain silent when he began answering questions after remaining silent for nearly three hours].)