Update, did some more readings in these forums, tried the AC3filter, it seemed to fix the problem, at least on the HD recordings I've tried so far, thanks
When I transfer HD recordings from my Tivo HD to my computer using Tivo desktop they play fine but there are no voices (background music is ok). I am using Windows 7. The same recordings play fine under XP (voices and music), just Windows 7 has this problem (64 bit if that makes any difference). Also strange, the COMMERCIALS seem to have voices, when it goes back to the show or movie the voices are gone. Other recordings (non HD) work fine under Win 7, voices and music. I'm guessing I need some sort of codec?