a great tool to convert ac3 and unprotected vob format files to wav pcm, mp3, wma and ogg vorbis formats. ac3 format file may contain up to 6 audio channels. ac3 decoder combines the information from these channels into two encoded channels, which deliver to each of your ears, via conventional stereo headphones, its own unique sum of direct and reflected sound from each virtual speaker. as a result, the listening sensation is much more natural.