What is the burden of proof in the context of consent to search?

In United States v. Shaibu, 920 F.2d 1423, 1426 (9th Cir.1990), we reiterated the burden of proof which the government must bear in order to show that a defendant gave effective consent to a search request. "The government must prove that consent was freely given. It must show that there was no duress or coercion, express or implied. The consent must be 'unequivocal and specific' and 'freely and intelligently given.' There must be convincing evidence that defendant has waived his rights. There must be clear and positive testimony" (quoting United States v. Page, 302 F.2d 81, 83-84 (9th Cir.1992).