Quoted from calico1997:

Regarding the amazing voice in the early 80's Bally games, especially Centaur and Elektra for example, I wanted to clarify this is almost certainly not Ken Nordine. I'm a huge fan of these games and of Ken Nordine, but I am about 99.99% certain the voice Bally used is the same guy they used in 1982 for Williams Sinistar - Mr. John Doremus. (He was a Chicago radio and voice talent that passed away in 1995, while by the way Ken Nordine is still alive and in his 90s).
They have similar voices, both deep. But Knordine has a more throaty voice while Doremus has a more nasal sound. Keep in mind the voices in the games are some times slowed down or otherwise modified. Especially in Centaur, you can really mess with the voice.
Here's a link of John Doremus doing a cheesy 80's promo video for a private school Fast forward about 1 minute into the video and then listen. It is clearly the Centaur guy's voice (without the reverb). It would be really cool if someone who knows how to make new roms sampled some of his words in this video and created new callout roms for Centaur!
» YouTube video
And of course, here he is in Centaur:
» YouTube video
And here he is (factually, as matter of record) as Sinistar:
» YouTube video

Quoted from calico1997:

I'm not aware of any digitally synthesized voice in the 1981 era that was human sounding. ... Sega at the time was the only game company with synth voice somewhat human sounding, but still more like a Speak and Spell machine.