What factors must be considered in determining whether a defendant's Miranda waiver is effective or ineffective?

To be effective, a defendant's Miranda waiver must be made ""'voluntarily, knowingly and intelligently.'"" (People v. Combs (2004) 34 Cal.4th 821, 845 (Combs), quoting Moran v. Burbine (1986) 475 U.S. 412, 421.) Avelino challenges the first factor. He contends his Miranda waiver was ineffective and his inculpatory statements must be excluded because they were involuntary. Relinquishment of Miranda rights, including the right to remain silent, "must have been voluntary in the sense that it was the product of a free and deliberate choice rather than intimidation, coercion, or deception." (Combs, at p. 845.)