[opendtv] Re: News: CEA FORECASTS CONSUMER ELECTRONICS REVENUE
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 12 Jan 2007 23:14:23 -0500
Olivier Houot wrote:
Where is the mathematical tool to compare - an initial "704x480"
analog SD signal occupying 6 Mhz of bandwidth
- a signal with a 1920x1080 resolution that has 6 times more
pixels but goes through a 50:1 compression step to finally force it
down into the SAME 6 Mhz signal as its SD counterpart?
Theoretically, there can be some doubt as to how much better
the second option is. After all, shannon will limit the amount of
information that you can squeeze through this limited bandwidth
in a given time interval.
I wanted to re-address this. I think what you're asking is perhaps not so
hard to compare, and the digital HD beats out the analog very convincingly.
First of all, I assume the 704 X 480 analog SD occupying 6 MHz more or less
represents NTSC. So in fact, it is 704 X 480 at 60i. And for good, clear
reception, in the 6 MHz channel, you need about 40 dB of C/N. Less than that
and the image quality suffers very rapidly, compared with an SD 480i.
And the video bandwidth is 4.2 MHz.
Compare that to 1920 X 1080 at 30p or 60i. The video bandwidth now is 31
MHz, and all you need to decode this essentially error free in a 6 MHz
channel is 15 dB of C/N, give or take a few fractions of a dB. And this is
very predictable, from what my STB's signal monitor tells me.
To me, that is the quick and dirty comparison. And it holds in real life, if
you look at the amount of power TV stations emit, analog vs digital, and the
resulting image quality *and* reception range.
The advantage of analog remains the graceful degradation, as we all know.
Bert
_________________________________________________________________
From photos to predictions, The MSN Entertainment Guide to Golden Globes has
it all. http://tv.msn.com/tv/globes2007/?icid=nctagline1
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