Dolby Digital 4.0:

In Dolby Digital 4.0 there is encoding for four discrete sound tracks through the AC-3 bitstream. When played through Dolby Digital equipment, sound is heard from all five speakers. The surround sound information is discrete monophonic. This means there is a separate channel devoted to the rear speakers but the information is sent to both rear speakers. The sound is very similar to Prologic giving less definition to the rear of the sound field. There are only a small number of titles in this format. There is also no sub woofer track present.