Quote:
Originally Posted by WS65711 /forum/post/17649858
So why does cable lose image quality? In my area, my cable picture is equal to my OTA picture as long as the image is static. As the degree of motion increases, the quality of the OTA picture is visibly superior to the cable picture.
Because they reduce HD image quality in a number of ways.
It varies, but many cable systems use 3 per QAM while others do that and real time rate shaping, and/or resolution reduction. I've even been told some cableco's pack 4 HD channels into a QAM.....
2 HD channels per QAM is considered a pass through that if done properly does not negatively affect HD image quality. Going to 3 per QAM is the rough ATSC equivalent of 12.7Mbps per channel, compared to a full ATSC payload of 19Mbps.
Comcast for example, passes local HD and some channels like ESPN, TNT, Versus at 2/QAM, and others come from Comcast Media Center (CMC) at 3/QAM; to my knowledge, they do not additionally compress HD with resolution reduction or rate shaping. CMC is a sophisticated system that uses state of the art technology from a central point to distribute channels via satellite and fiber across the nation. It's not ideal, but it compares very favorably to most other options, except Verizon FiOS, which is the only national HD provider that does not additionally compress or otherwise reduce HD image quality when received from the source.