How many people are going to comment that his voice sounds different? Have you really only ever seen him on The Office? Yes, his "Jim" voice was very low and extremely quiet. He says many things under his breath. That is called playing a character. Also his voice was a bit huskier then. He is louder and projects in front of a live audience. Also he's a voice actor and director so he's often shouting into megaphones on set, and probably overextending it. It's a bit more course and raspy these days. Probably the only real difference.
