What is it specifically that the HD box does to the HD signal to enable HDTVs to have such great picture quality?
The HD box is sort of like a choirmaster. Imagine thirty 5th graders all standing together on a stage singing whatever holiday songs they want without any direction. It would sound like a busy fish market. The choirmaster (the HD box) has the ability to tune in one particular little girl’s pure voice singing a particular song from all the noise, and then filter only her voice for her mom and dad who are listening in the audience so it sounds like a beautiful solo.
Some kids have low-quality voices (standard-definition TV signals), while other talented children who have gorgeous voices should have an agent and sing on Broadway (high-definition TV signals). The HD box decodes the inbound digital signal for a particular channel and isolates it from all the rest. When the signal is decoded, there is more sound and picture available coming in from the source to display a high quality HD picture with surround sound.