What is the procedure for the trial court to determine outside the presence of the jury as to whether or not to hear evidence in a confession case?

"Evidence Code section 402 provides a procedure for the trial court to determine outside the presence of the jury whether there is sufficient evidence to sustain a finding of a preliminary fact, upon which the admission of other evidence depends." (People v. Galambos (2002) 104 Cal.App.4th 1147, 1156.) Specifically, the statute provides that "[t]he court may hear and determine the question of the admissibility of evidence out of the presence or hearing of the jury; but in a criminal action, the court shall hear and determine the question of the admissibility of a confession or admission of the defendant out of the presence and hearing of the jury if any party so requests." ( 402, subd. (b), italics added.) As in the present case, "[i]n situations not involving confessions or admissions going directly to the crime charged, it is within the trial judge's discretion as to whether he will initially hear evidence outside the presence of the jury as to a preliminary fact that may bear upon the admissibility of proffered evidence." (People v. Slocum (1975) 52 Cal.App.3d 867, 888; accord People v. Williams (1997) 16 Cal.4th 153, 196.)