[opendtv] Re: 20040722 Thundering Thursday Thanks (Mark's Mon day Memo)

  • From: Eory Frank-p22212 <Frank.Eory@xxxxxxxxxxxxx>
  • To: "'opendtv@xxxxxxxxxxxxx'" <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 23 Jul 2004 12:42:54 -0700

>From: "John Willkie" <johnwillkie@xxxxxxxxxx> 
>To: <opendtv@xxxxxxxxxxxxx> 
>Date: Thu, 22 Jul 2004 16:38:18 +0100 
>I would expect them to have the same hiccup as OTA.  That doesn't mean they
>can't create their own.  One I know about, vis a vis Cox San Diego:
>stripping out PSIP.  I would assume they also remove null packets.

Of course they would need to strip out PSIP and re-send that data as out of 
band SI, so a digital cable STB could understand it. Likewise, I would assume 
they remove null packets and that they remultiplex program streams to optimally 
utilize their RF channels, which have a much higher data capacity than DTV RF 

>I recall from previous posts that you're on the HDTV tier, so you have a few
>channels without the compression artifacts that makes digital cable seem to
>be to be of lower quality than analog.

I have 10 HD channels, a bunch of SD digital channels and the standard 60-ish 
analog channels. Compression artifacts are rare and in general the SD digital 
channels look to be about the same quality as analog. 

>The nut of the issue would be why, to you, HDTV in a transport with SDTV
>seems lower quality than HDTV with no other program service.  Logically,

HDTV at 13 Mbps is not the same as HDTV at 18 Mbps. To fit the lower data rate, 
one must either lowpass filter before encoding, or allow compression artifacts. 
Since my "pseudo-HD" ABC and PBS channels simply look 'softer' and have few 
compression artifacts, I assume the local broadcaster is pre-filtering them 
before encoding. Either that or the network is doing it before it reaches the 
local broadcaster, which I doubt.

>I suspect the problem is at the cable company, and I would want to check the
>path and signal processing that each transport undergoes.

OTA viewers around here report the same experience regarding the relatively 
picture quality differences between the various OTA HD channels.

>  The cable company
>has an incentive, do they not, to make multiplex broadcasting work below
>optimal?  After all, they do filter out the dangerous second streams to
>prevent them from inflicting their viewers, do they not?

They might have such an incentive if they were desperately squeezed for 
bandwidth, which I do not believe is the case on my local Cox system. They do 
not retrans the "dangerous second streams" because those programs are not HD 
and in many cases those programs (but not necessarily those bits) are already 
carried at the same resolution on another channel. Cox is offering "HDTV 
service," not "DTV broadcast multiplex carriage service." If I want to watch my 
ABC affiliate in HD resolution, then channel 15.1 is there on Cox's HD tier. If 
I want to watch my ABC affiliate in SD resolution, I don't need Cox to carry 
15.2 SD -- I can just watch it on analog 15. It's the same program at the same 

>Deteriorating a HDTV stream -- if that is what is occurring -- would be a
>significant FCC problem for them.

Which is precisely why I don't believe Cox is doing anything to deteriorate 
them. Unfortunately, there is no equivalent FCC problem for a local broadcaster 
who deteriorates the quality of the network HD feed, just so he can multicast 
an HD and an SD program on his DTV channel.

-- Frank
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