The Evolution of Digital TV and HDTV
We all love the incredible video quality of High Definition TV (HD), however, since HD is not mandated within the Digital Television (DTV) plan, it allows a broadcasting station to use the allotted 6 MHz space (for the HD channel), to multicast instead several sub-channels of lower SD quality, as is actually happening on many stations across the US. When sharing the same 6MHz total bandwidth, SD sub-channels rob about 2-3 Mbps each from the needed bandwidth of an HD channel that by itself should broadcast at 19.4 Mbps (if the station also multicasts an HD sub-channel). The parallel broadcast forces further compression of the 19.4 Mbps HD signal to a lower bit rate to make room for the SD sub-channel, compromising HD quality. In many cases, more than one SD sub-channel is multicast together with the HD sub-channel. When the reduced HD bit rate compresses the signal beyond acceptable limits, it renders a lower quality image with noticeable defects, especially on fast moving images in sports, which are more evident, and unacceptable, on large screens. It might also be possible that the TV station desires to share some of the bandwidth for data-casting interactive services, or for mobile DTV applications for hand-held portable devices because there will be no analog broadcasting to those portable devices as well. We all hope that HD will reign, and HD quality will prevail over the digital-quantity business models, and you have to encourage DTV broadcasters to do so, besides, most consumers bought an HDTV not a SDTV.