Ok, sorry Renee, what you read there, it is... well... advertising.

Not technically wrong, but not quite up to the everyday reality either.

What xVAsynth does, is generate voice files from text lines that you type into your quest window in a wide range of games. Certainly Morrowind, Oblivion, Skyrim, Fallout, to name a few, which is what we care about here. Here it is
on Nexus.
For it to work, it requires what is called "voice models" - data files based on actual voice lines recorded by actors, such as all the different voice lines for each race in Oblivion. There is a different tool that allows you to create these models - to train them, as it is called. So if you wanted to, say, take Geralt's voice from The Witcher and make him say new lines for your mod, you would first need to train a "Geralt" model and then use it to generate your new lines.
That's too complicated for me though.

I just use models that someone else already created. Previously those models were not very good, so the newly generated voice lines sounded very mechanical. But recently both the engine and the models for Oblivion got revamped and improved, and can now generate quite acceptable voice files. I believe Skyrim voice models are even better, and that's what Ghastley is using to voice his mods.
But to start with, you need those text lines exported from your quest window into a very specific format that the voice synthesizer can read. And that's a job and a half already!
It is also possible to hand-craft each line, tune parameters until you're happy with the way it comes out. I don't have that kind of time! But Ghastley does.
I think Zelazko is also using it, so that's three people already, and I figured we might want to exchange tips. Hence this thread.