杜比数字EX是在
杜比数字（dd）的基础上发展的一种新型
环绕声系统。由于添加了一路后置音箱，环绕声效果更为显著。
杜比Digital EX就是在杜比5.1基础上增加了一个
后置环绕，增加的我们可以认为是“后中置”，这样完成了从杜比5.1六声道向
杜比6.1七声道的升级。有了这个后置中央声道，我们欣赏大片时可以用身心感受后置左右声道之间的重要过渡和暗示信号，从而体会到真实的现场感，用一个词来形容就叫做身临其境。
目前支持
杜比数字EX的影片已有不少，如《飘流者》《角斗士》《星战前转》《魔戒指环王》等等等等……个人觉得新格式普及得非常快，就像AC-3取代
杜比定向逻辑、DTS大量涌现一样，没有一点超前观念是不行的。当然，这个后置声道不仅仅在大片中才起作用，一些新的游戏配合Audigy2的EAX ADVANCED HD技术让背景声更丰富，定位更精准，这些游戏包括《Unreal Tournament2003》（虚幻竞技场2003）《Tomb Raider: The Angel of Darkness, Neverwinter Night》（古墓丽影：黑暗天使）很多…… 。
Dolby Digital EX takes the Dolby Digital 5.1-channel setup one step further with an additional center surround channel (reproduced through one or two speakers) for extra dimensional detail and an enveloping surround sound effect.
Feature films originally released in Dolby Digital Surround EX (the cinema version) carry the encoded extra surround channel in their subsequent DVD releases, as well as onto 5.1-channel digital satellite and TV broadcasts. If your home theater system has a receiver or preamp/processor with Dolby Digital EX decoding and speakers to support 6.1 or 7.1 playback, you can hear Surround EX soundtracks as they were meant to be heard, with the increased realism created by the extra surround channel. As in the cinema, with regular 5.1-channel Dolby Digital playback no sonic information is lost (although you'll miss out on the heightened realism).
Current Dolby Digital Surround EX soundtracks contain a digital flag that can automatically activate the EX decoding in a receiver or preamp/processor. For titles released prior to late 2001, however, you need to turn on the EX decoding manually.