What is the test for determining whether an accused waived his right to counsel and remained silent before making a statement to the police?

As stated in People v. Debnam, 261 Cal.App.2d 206, 212(8), 67 Cal.Rptr. 692, 696: 'The question whether an accused waived his right to counsel and his right to remain silent before making a statement to police officers is primarily a question of fact for the trial judge.' Likewise, in People v. Drumgo, 269 Cal.App.2d 479, 482(3), 74 Cal.Rptr. 761, 763, it was said: 'The court in this case observed the witness (appellant), heard him testify, heard and saw the officers testify with reference to whether appellant made an intelligent waiver of his privileges and rights. It is a question of fact and the judge is the person under the circumstances in this case to ascertain the credibility of the witnesses.'