[mythtv-users] OT: Comcast local QAM - would they still send signal if I cancel?

Deyan mythtv at bektchiev.net
Mon Jul 26 21:40:13 UTC 2010


> > content in a single channel is due to their practice of degrading the
> > quality of said content.  I have seen the difference between OTA and
> > Cable, and it is very noticeable.
> >
>
> This is only partly true. Since cable has a higher signal to noise ratio
> than OTA, they can use QAM256 and get more data through
> the link than 8VSB, so potentially they could send 2 HD signals in the same
> bandwidth that would allow only one for 8VSB at
> about the same quality.
>
> But then comcast goes and tries to cram 3 HD signals in that bandwidth.
>
> QAM256 has ~38Mbps total bandwidth compared to just over 19Mbps for 8VSB
this is correct. However in the 19Mbps OTA networks usually run 1 HD and
usually multiple SD streams so the actual bandwidth that they use is more
like 12-15Mbps and then it's not that hard to put 3 HD OTA channels in the
same Cable channel with virtually no loss in quality and I imagine you'd
only have issues if all three of these show  simultaneously high action
scenes where the total bandwidth of the three would exceed 38Mbps.

Here are the actual values for SF Bay Area broadcasters that one person
provided on the SFBayHDTV Yahoo group about a year ago (the numbers are all
in Mbps). As you can see only few of these ever go beyond 12Mbps (I don't
have numbers for Cable/Satellite only HD channels so there the bandwidths
may be different) and this is during prime time:

2-1 = variable 14 - 14.5
2-2 = 2.05

4-1 =  3.62
4-2 = 14.32

5-1 = variable 11 - 17.5

7-1 = variable 11 - 12
7-2 = variable  4 -5
7-3 = variable 1.5 - 1.7

9-1 = variable 9 - 11.5
9-2 = 3.03
9-3 = 2.84

11-1 = variable slightly 12.7 - 12.8
11-2 = variable slightly  3.2 - 3.4
11-3 = variable slightly  2.3 - 2.4

20-1 = 14 -15
20-4 = 2.46

36-1 = variable 9.5 to 13.5
36-2 = 3.22

44-1 = 16 - 17

48-1 =  3
48-2 = 15

65-1 = variable 9.5 - 11
65-2 = slightly variable 2.4 - 2.5
65-3 = variable 2.5 - 3
65-4 = 1.9
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