Well, I learned something new today. Yep, you are correct, Lamb! From the birds in the forest, actually.
*rolls eyes* I like Alex's voice in Redux, TSL and 6. You have to remember, he was a slave. He probably wasn't allowed to sound like he was emotional to his master, lest he start eyeballing him and start thinking he's a threat if he raises his voice or puts energy into it. Heck, if you try to talk in Manannan's house (just to the environment in general) it says something along the lines of, "You learned not to raise your voice a long time ago." He probably wasn't really meant to say anything much to his master, other than "Yes, Master." "No, Master." enc. And I know it wasn't you, but someone said a long time ago that Alex spoke "barely above a whisper" in 6. Uh, maybe it's because I have really good hearing, but I can hear him just fine. He's softspoken, yes, but he's not whispering.
And as for why he still presumedly speaks that way after freeing himself, it could just be his mentality of still thinking himself a slave and keeping his voice soft and flat like he'd been told to do.