Please note that using certain encoding/decoding technology in some countries without first paying the appropriate license fees may mean that you are infringing on various patent holders' rights. Please check out the situation in your country first.
VOB files (from DVD) may use an AC3 audio stream, which require a DirectShow filter on your system. A free AC3 filter can be downloaded at the site linked in Step 1. Simply install the AC3 filter on your system, change the important optimum quality settings as per below, and Ots Studio will convert the AC3 audio stream to MP3 during the conversion process.
IMPORTANT NOTE: Don't forget to follow the other important quality-settings steps below after downloading and installing.
Download the AC3 Filter installation file from here.
Run the installation file.
Launch the configuration dialog by going to Start->Programs->AC3Filter->AC3Filter Config
Under the Main tab, change the Output/Sample format to PCM Float. Under DRC make sure Enabled is unchecked, or Uncheck the Use DRC checkbox (in older versions).
Under the Mixer tab, uncheck Auto gain control.
Output format in both of these tabs should be at 2/0 - stereo.
Save settings, and you should be ready to start importing AC3-audio VOBs! You may need to restart your computer first.