Mm, Hitler's voice here sounds ethereal, almost disembodied...
Notice how every time Hitler speaks here, his voice doesn't really seem to come from the actor, but feels like it comes from everywhere, like a narrator? And also, unlike his public speech voice, sounds very relaxed, calmed, even reasonable?
Gives him an extra creepy quality.
And in fact, it does sound closely to Hitler's REAL normal voice (not his public speech voice):
https://www.youtube.com/watch?v=ClR9tcpKZec
Eerie, isn't it? I liked it.