Before revision: Rear/back center channel 6.1 channel surround systems such as Dolby Pro Logic IIx and Dolby Digital EX use a single rear surround channel in addition to the traditional left and right surround channels.
After revision: Rear/back center channel 6.1 channel surround systems such as Dolby Pro Logic IIx ,and DTS-ES Dolby Digital EX use a single rear surround channel in addition to the traditional left and right surround channels.