Left, Center, Right, Surround. The four playback channels used in 35mm motion pictures, now available on home hi-fi systems. L, C, and R speakers are located behind the screen. The S channel surrounds the audience and may be mono or encoded stereo. See matrix, surround-sound. Variants include LCRC, when the fourth track is to be assigned to the center, or even CCCC, as in a center-channel dialog premix.