The late `Thriller` hitmaker - who died of acute Propofol intoxication last June - spoke with a deep, masculine tone but altered the pitch in public so people would like him more, says his biographer Ian Halperin.
He said: "He wanted to act like a boy. He felt it was a way for the public to like him more."
Michael`s spiritual advisor, Reverend June Gatlin, added: "His voice was not high pitched. It was deep - a real man`s voice."
June - a self-proclaimed "seer" - says the singer visited her in Los Angeles for "spiritual cleansing" so he could be himself and speak in a normal voice.
Ian - whose documentary on the singer, `Gone Too Soon`, was air on the anniversary of his death on 25.06.10 - added: "She tried to get him to be just Michael."
Meanwhile, Michael`s brother Randy Jackson has expressed his disappointment that Dr. Conrad Murray - the physician who has been charged with the involuntary manslaughter of the singer - was allowed to retain his license to practise medicine by a Los Angeles judge last week.
He said: "The recent court proceedings have been difficult for us as a family.
"However, it is a necessary process that we are well prepared to endure in our fight for justice for Michael."
Los Angeles Superior Court Judge Michael E. Pastor claimed he had a lack of authority to suspend the doctor`s license, despite calls from the California Medical Board and state Attorney General Jerry Brown to do so.
Despite the ruling, Randy said he and his family still has "continued respect and faith" in the judicial system.
A preliminary hearing for the medic is set to take place on August 23. If he is found guilty of the involuntary manslaughter of the singer, he could face up to four years in jail.