"Muffling" Voices?

Sorry if my question’s really obvious XD [I’m pretty new to Audacity so I’m not familiar to the functions…] But anyways, I was wondering how can I “muffle”-ish voices like the one in this video [:49~:54]:
http://www.youtube.com/watch?v=7W8IOi5gR-s

Thanks!!

Not exactly muffling. I’d be looking at a vocoder effect.

http://www.youtube.com/watch?v=VvqjjrOZNxc&feature=related

I think there’s one built into Audacity 1.3.12. You need two sounds. A base sound like his guitar and then the modulating sound which is his voice. You can use any two sounds for either one.

Koz

Thank you!! hugs