Guide: How to Use DVD to AC3 Ripper to Rip DVD to AC3?
Tips: If you are a Mac user, you can try the DVD Ripper for Mac.
Preparation: Free download, install, and then launch it.
Step 1: Load DVD files
Click the "Load DVD" button on the toolbar to import DVD into the DVD to AC3 Ripper.

Step 2: Setup the output parameters
Click the "Profile" -> "Common Audio", and then choose AC3 as the target audio format.
Click the "Browse..." button to set the root directory for the converted files.

Step 3: Start converting DVD to AC3
When everything above is set up all right, just click the "Start" button to start to extract AC3 from DVD.

Not only can convert DVD to AC3, the DVD to AC3 Ripper also can Convert DVD to FLAC, Convert DVD to AAC and other audio format with the original DVD quality. Furthermore, it can also convert DVD to video format and video format which is acceptable for popular portable devices.
If you want to have a try, you can get the DVD to AC3 Ripper for free.