A simple description of home theater sound system As the technology of audio and video reproduction advances, things have gotten more complicated. Monophonic tube radios evolved into stereophonic Hi-Fi systems, which in turn evolved into multi-channel surround sound systems, like 5.1 and 7.1 etc. The most recent advance in surround sound is an '' IMMERSIVE SOUND" -- reproduces sound in all directions, not just in front of and behind the listener, but also above the heads too, popularly known as ATMOS and the numerical shorthand is coined and named as 5.1.2 or 7.1.4 and The format is "x.y.z" where: "x" is the number of channels or speakers at or near ear level, "y" is the number of channels or speakers dedicated to low bass reproduction "z" is the number of overhead channels or speakers