Change the settings so voice plays through your speakers and headset so the PVR records other people's voices. To record your own have your (if you have a turtle beach) hooked up to your computer and record your voice separately (audacity). Then overlay your voice on the video, remember to match it up. Mine is a bit off.
Also, I'd recommend turning down the game volume a lot, unless people with you speak loudly. Mine wasn't turned down enough... Or you could just not have the game music at all.