So I was looking at the thread about the changes in Vader's suit and was directed to the Secret History of Star Wars site's area about Vader. There I found these quotes:

Return of the Jedi gave us some slight modifications as well, notably a further enhancement of the vocal flanging to make it seem more processed and electronic than in Empire Strikes Back, perhaps because the unmasking scene at the end would reveal a design that shows that Vader's natural voice is processed and amplified through an electronic system.

...

Finally, Star Wars was altered where possible to match the depiction seen in the subsequent entries--James Earl Jones' voice was enhanced for the 2004 DVD release to sound more like the electronic version of Empire Strikes Back, Return of the Jedi and Revenge of the Sith .

I know Ady said that he modified Vader's voice in the ANHR DVD-9, but me being the dense person I am have not been able to notice the difference.

Ady, are you going to modify Vader's voice in ESBR to match RotJ, or does ANHR match ESB so now you need to unprocess RotJR? Not like I ever noticed the difference, but I'm just curious.