A subset of the Dolby AC-3 sound playback standard (a.k.a. Dolby Digital), and the specific format sound data is in that corresponds to that standard. This is the current state of the art home theater surround sound technology. It means that there are five channels of information (left, center, right, left rear, right rear) and one active sub channel (the .1 channel). It is also a major standard that is becoming part of the DVD standard, which means there will be numerous releases in this format for the next few years.