How is Surround EX decoded?
Surround EX decoder takes the discrete left and right surround channels and outputs left, back and right surround channels. The SA10, Dolbys EX decoder for cinema theaters, uses standard Dolby Pro-Logic in which the back surround channel (rear) is extracted in the same way the front (screen) center channel is derived form the two-channel Dolby Surround soundtrack. WSR #32. Info that is in phase and equal in both l/r discrete channels is steered to the back channel. To ensure non-EX sounds (l/r surround effects) are not pulled into the back channel the l/r surround channels are encoded with a phase shift of +/- 45 degrees. This prevents full steering to the back surround (which would create a mono-blob type effect) and at the same time keeps the sound from being pulled to the Extra channel.
