[opendtv] Re: News: CEA FORECASTS CONSUMER ELECTRONICS REVENUE
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 14 Jan 2007 08:07:03 -0500
At 5:46 PM -0500 1/13/07, Albert Manfredi wrote:
Rubbish. Take a look at a spectrum analyzer of ANY MPEG-2 encoded
HD source with a bit rate of say 17Mbps (about the max video
payload for ATSC). The only stuff you will see above 20 MHz ...
So, did you do the same test with 4.2 MHz in NTSC?
Certainly. With proper NTSC equipment calibration you should see
undistorted content all the way out to 4.2 MHz, then a nice smooth
roll-off down to about 8 MHz.
With good ITU-R.BT601 gear you should see flat response out to 6.25
MHz, then a smooth roll-off.
I'm baffled by this persistent refrain.
Maybe its time you stopped spouting off about theory and spent some
time understanding the new trade-offs with digital encoding.
The C/N of the channel is completely irrelevant to this discussion -
the frequency response is no longer a function of an analog channel,
it is a function of the digital encoder.
I agree that the frequency response of the video signal is no longer
directly related to the bandwidth of the RF channel in MHz. But you
missed the entire point of Olivier's musings, which I actually found
rather interesting.
The Shannon limit certainly does come in play.
You can't fool mother nature. The rules don't change when we move
from analog to digital. For any transmission channel you have
theoretical limits, and the practical limits that can be achieved
based on distortions and transmission losses. We have moved into a
digital world where we can decouple the source from the channel
distortions, but to get there, we had to compromise in other areas to
make the content fit the bit rate.
Regards
Craig
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