Searching for an easy way to convert DTS audio to AC3, you will find a great and free application called PopCorn MKV AudioConverter. You can download it here.
Many video files in MKV like movies or concerts contain DTS audio and some setup boxes or old A/V receivers can’t decode it while AC3 is a more standardized format, even for old players.
By using this tool, only the audio will be converted and then remuxed again to a new MKV file, while the video will remain untouched.
Using PopCorn MKV AudioConverter is as easy as it gets. When you open it, it will automatically download all the needed files and tools. Then, its just a matter of specifying the source file, the destination file and deciding whether or not you want to keep the original DTS audio track inside the MKV file along with the new AC3 audio.
You can choose a file or a folder if you want to convert many files at once. If you want to keep the original DTS track, make sure to select the checkbox Preserve DTS Track.
When you are ready, click the Run button and the process will begin. It only takes between 5 or 10 minutes for 1 file depending on your computer.
You can use it to convert DTS audio in other formats, not only DTS, if you want to.