Michael purposely spoke in a higher tone to perserve his vocal cords for singing, but he was very capable of speaking/singing in a deeper voice & going right back into a higher voice. Here's Exhibit A & Exhibit B:
This is random AF but I really like that they did not lighten his skin for the Bad Era portion bc I feel like something most people don't realize is that MJ was still pretty brown in the late 80s, albeit a lighter shade #MichaelMovie