I don't know if the Google generated voice is correct, but comparing it to this lesson, the word definately sounds like "votar".
I do hear a difference between the two; the «ol» in «voltar» sounds like the English "Oh!" while «votar» does not have this diphthong. I would not recommend Google Translate, though, since their robot voices are not always clear. forvo.com, on the other hand, is great because it has native recordings from diverse regions.
Admittedly, it is difficult to hear the difference between the two for Portuguese learners. In European Portuguese, the distinction is clearer as the «o» in «votar» is pronounced like English "oo," and the one in «voltar» like the "aw" in American English "law."