It's some kind of voice synthecizer, but I couldn't find it, would love to find out too though.
I believe it's SAM, a text-to-speech programme that was used on consoles like the Commodore 64 and Atari :)
I just looked it up and tried, it sounds just like the game's voices! Or the contrary, but you get the point. I bet that's what they used for the voice acting, even makes sense considering the Atari aesthetic.