Sound Filter for DVDs - FREEWARE

AC3Filter is an open source AC3 decoding filter that allows you to watch videos with AC3-encoded surround audio. It is a DirectShow AC3 Decoding filter used to playback AVI files with AC3 sound tracks and DVDs. It also has Multichannel and S/PDIF support. The Filter is focused at flexible controls during playback like gains, mixer, stream information, levels and others. AC3Filter is distributed under General Public Licence, thus is absolutely free.

http://jaist.dl.sourceforge.net/sourceforge/ac3filter/ac3filter_0_66b.exe