Dolby Digital Surround EX adds a third surround channel to the Dolby Digital format. The third channel is reproduced by rear-wall surround speakers, while the left and right surround channels are reproduced by speakers on the side walls. Among the benefits are more realistic flyover and flyaround effects and a more consistent surround field throughout the auditorium. adds a third surround channel to the Dolby Digital format. The third channel is reproduced by rear-wall surround speakers, while the left and right surround channels are reproduced by speakers on the side walls. Among the benefits are more realistic flyover and flyaround effects and a more consistent surround field throughout the auditorium.