In Star Trek: Discovery, a lot of the time when Michael Burnham is alone with another character she starts whispering. Why does she do this? Is it something the actress has done in other roles?
Michael is a direct speaker and rather than yell, she prefers a hushed, yet firm, tone when she talks to people to sway them to her side. Remember, she was raised for a not-insignificant time on Vulcan, and the Vulcans love to speak directly to people in calm tones. It's one of the few traits that has been consistent about the character since her debut
As you can see from this interview, Sonequa Martin-Green (the actress) is quite a bit more... bubbly in personality.