(Sony Dynamic Digital Sound) A digital audio encoding system used in movie theaters since 1993. The SDDS sound track is recorded optically as microscopic pits similar to a CD along both outer edges of the 35mm film strip. An SDDS reader is mounted on the projector, and red LEDs read the pits and convert them into digital data. Using a 5:1 compression, SDDS supports 6-channel and 8-channel auditoriums. No home theater counterpart is expected. See Dolby Digital, DTS and THX.