Sony Dynamic Digital Sound. Developed by Sony, the SDDS split-surround format uses the usual 5.1 stems, plus additional left-center and right-center channels. The additional two speakers are employed at the front of the soundstage to deliver more uniform sound in wide-format theaters of screen widths of up to 60’ or more, where there might be seats with a hole-in-the-middle in between the C-L, and C-R channels. An important aspect of the SDDS format is that it can be decoded into four, six, or eight channels for playback on a wide variety of audio systems. Proponents of this format claim that the extra front channels make a significant difference in the amount of depth, fullness and natural image of the audio.
See 7.1.