#plus there's the fact that ras was constantly irritated in part 1 due to everyone in imperium either being useless or not doing what he say

[toastingpencils37]

Random theory for why in canon (not talking about the VA) Ras voice is different from DR part 1 to later.

In Part 1, while he was still in Imperium, he had to build up a menacing reputation for himself. Thus, the deeper and more growly voice.

But later, in Part 2 and onwards, he doesn't have to do that as much, as he doesn't have as much social power as he did then. And even when he's talking to Jordana, he doesn't have to be as threatening to her, but more generous, as he's offering her a chance to use what she extracted from the source dragon. Plus, that reputation he previously had, is still somewhat there.