Quote:
Originally Posted by coco
For example, one of the NBC stations of my childhood added CBS as a sub-channel during the digital sub-channel. Virtual 5.1 is NBC at 1080i. Virtual 5.2 is CBS at 720p
You are talking about KALB out of Alexandria,LA. I can catch them a couple of nights a week.One of the stations ' audio broadcast is much higher than the other. Here is my tv fool report
http://www.tvfool.com/?option=com_wr...b7c8610a10029f |
Are you asking for help to improve the audio of KALB RF35's audio on virtual 5.2? Two issues:
- You can receive KALB only via tropospheric ducting. Tropospheric ducting is an anomalous atmospheric condition that allows RF signals to travel great distances. This explains why you receive it only on occasion.
- You do not separately receive the various KALB subchannels. There is nothing that you can do to differentially improve your reception of one subchannel without improving reception of them all.
Tropospheric ducting does not explain why KALB-CBS audio is subpar. The audio is subpar because that's how KALB broadcasts it. This brings up a larger issue that has been well-known since the early days of commercial digital broadcasting. Bandwidth is limited. ATSC, the North American digital broadcast standard, uses the same channels and bandwidth as the NTSC analog broadcast standard. This 6 MHz bandwidth/channel is more than ample for 1080i or 720p HD broadcasts. Enough bandwidth is left over for one or two subchannels. Cable providers squeeze in 27 standard definition digital channels using QAM within this same 6 MHz bandwidth. However, 6 MHz is not adequate bandwidth for more than one broadcast HD subchannel. The only way for KALB to squeeze-in both NBC-HD and CBS-HD is to leave out something. A standard cheat is to compress the bandwidth required for each HD-subchannel. The network sends down multichannel digital audio. Digital audio doesn't require a lot a bandwidth but it does require some. When they are squeezing, that lovely 5.1 audio may be reduced to 2.1 or less.
This is why HD cable does not look as good as HD-OTA. Cable also uses 6 MHz bandwidth per channel. However, cable providers compress at least two HD channels within each 6 MHz channel. The most obvious artifact of this practice is the gross pixellation of fast-moving action.