AC3filter is an audio decoder and processor filter that enabled media players to play AC3 and DTS audio tracks. Basically, this is used only for AUDIO files, but since AUDIO is present in movies and videos, the AC3Filter will allow you to experience the true quality of a DTS enabled media file.
The installer of the application automatically adds the codecs and the drivers to your system. The only thing you have to do is go to Start and type AC3Filter Config.
The configuration window will look like this:
You can use this control panel to adjust various settings related to audio output, volume gain, equalizer, compatibility, audio support, etc.
If it's enabled and you play a file with DTS support, then you'll experience a totally new sound quality.
I kindly recommend using the HELP button for an in-depth view of the possible configuration.
Main Features page: http://www.ac3filter.net/wiki/AC3Filter#Features