OT: Composite/Component [was Re: [mythtv-users] Re: Image quality, what effects it?]

Jay R. Ashworth jra at baylink.com
Fri Aug 13 15:08:23 EDT 2004

On Fri, Aug 13, 2004 at 08:31:54PM +0200, Rudy Zijlstra wrote:
> >Yeah.  The PcHDTV card is probably doing that.
> >
> No, it is not. It is receiving a 2, 4,  8 or 16 VSB modulated MPEG-2 
> Transport stream according to the ATSC standard and selecting the wanted 
> PIDs out of it.

Oh, of course: that card has to *decode* MPEG, which is (by design)
much easier.

> SW support is only for 8-VSB (the only modulation currently used on 
> ATSC), which limits the TS to 19.4 Mbit/s. This means the card is 
> specific for terrestrial ATSC. On a cable the signal is likely to be 
> re-modulated in QAM-64. QAM-256 might also be used. Most cable companies 
> use QAM for digital modulation and will not support 2 different 
> modulation schemes at the same time. Also the ATSC standard (at least 
> when last I looked at it) does not mandate any particular modulation 
> when used over cable. For terrestrial use VSB is mandated. Sattelite 
> uses QPSK (QAM-2) modulation.

I believe SCTE-40 specifies QAM-64, yes.  I do wish someone would do a

And this a-la-carte cable crap...

-- jra
Jay R. Ashworth                                                jra at baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

	"You know: I'm a fan of photosynthesis as much as the next guy,
	but if God merely wanted us to smell the flowers, he wouldn't 
	have invented a 3GHz microprocessor and a 3D graphics board."
					-- Luke Girardi

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