Okay a couple of posts back someone was talking about Yami's voice going deeper and a bit huskier and Yuugi's voice going higher. Well I'm soon to have a recording of present Yami and First episode Yami but man, just listening to him and Yuugi their voices have changed and thus I have created a theory.
When Yami arrived Yuugi was finishing up puberty, his voice hadn't completely hit the low belts yet, and so over the time that Yami has been sharing a body with Yuugi, he has been stealing his puberty. So Yuugi's voice goes up while Yami's goes deeper with all the puberty he's stealing.
Damn puberty stealing Pharaoh. Get your own darn puberty. Maybe he's just trying to catch up with Kaiba and Bakura with manliness by trying to steal more puberty....hmmmmmmmm.