penumbra audio problem

[Japface]

hi, i just bought the penumbra series on steam, but when i start a new game, namely overture since thats the only one i've tried it with, the voice acting in the video starts off normal, and then it speeds up. when i say it speeds up, i mean its incredibly fast, and sounds like a chipmunk is reading the lines.

its kind of hard to play the game and absorb the story when that happens. i can consistently reproduce this when the game starts, and would rather wait to play it until i know how to solve the problem.

i bought this during the steam christmas sales. any help would be appreciated.