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RE: History of 29.9





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From:   INTERNET:telecine at alegria.com
Sent:   Saturday, February 14, 1998 7:26 AM
To:     multiple recipients of
Cc:     "'craig at pcube.com'"
Subject:        RE: History of 29.9

This also reminds me of a story I heard yesterday:  If you look only at the
electricity bill of a typical analog NTSC station you'll find it's a big
number.  (Many many kilobucks per month to drive the transmitter.)  As
stations and markets convert over to DTV there will be a time where the old
viewer base gets down toward the 10-20% number, where it will probably
linger for a long time, maybe well after 2006.  (That is, 10-20% have NOT
bought a new DTV set and rely on the older analog NTSC service.)  There
will
be a big incentive for the TV station to drive that number toward zero or
at
least under 5% so they can legally shut off that service if only to save
the
power bill.    Depending on the market, one possibility is for them to buy
set top boxes and give them away to their viewer base.  Cheaper than
keeping
NTSC going in the long run.  But then by definition those STB's will still
be driving older analog NTSC television sets, many of which will lose their
mind if you try to drive their NTSC inputs at 60.00 Hz.  The STB's can
receive the new DTV service at 60.00 Hz but I seriously doubt if they will
perform a framerate conversion between 59.94 and 60.00 in a $300 box.  So
what they are going to do is drop frames.  Those viewers will simply have
to
tolerate the artifacts.  They pay for the old decisions yet again.

New chip sets developed by Sarnoff Labs and being manufactured by Motorola
and Lucent Technologies for set-top boxes will display all of the formats
in the DTV spec. on your existing set. If it is 4x3 then thats what you'll
get. If it's a wide screen but not HDTV it will give you wide screen.
DirecTV set-top boxes have that built in already. (Look in your setup
menu.) So I think your concern has no real worry and DTV will eventually
replace the analog NTSC.

Eight of the formats in the ATSC's emission format specification, Table 3,
are 704 pixels per scan line as opposed to 720 pixels per scan line like
the
SMPTE and ITU production specs say they should be.  In other words 704
pixels by 480 lines instead of 720 pixels by 480 lines.  Not a big number
but unless that gets changed now we'll have to live with that (just like
59.94) for at least half a century to come and probably more.  The 480 line
formats are going to be where the bulk of DTV programming happens.

704 pixels takes into account the rise time of horizontal blanking. If the
signal had an infinate rise time you would have 720. If you see a film in a
theater its like the fuzzy edge of the frame on the screen when the film is
sharp. The FCC has a spec for the horizontal rise time of the blanking
pulse.

The ATSC spec for 50Hz countries is the full 720 pixels.  Most other
nations
and broadcast standards have adopted 720 pixels.  There is zero technical
reason to stick with 704 in the US.  Bizarre.  Here we go again.

I believe that 704 really is dependant on the MPEG 2 encoder. The MPEG 2
decoder could care less. Besides thats only 8 pixels on a side or less than
3% of the picture width which is well beyond the safe action window.

Similarly, the ATSC has a specification for its AC-3 audio bitrate that is
lower than what consumers will be buying on DVDs and other sources.  Again,
it is not a big difference but why not fix it now instead of letting it
linger?  Why should the new DTV terrestrial service have an inferior
quality
level to any other form of digital entertainment?

AC-3 is the standard for the DVD as well as the DTV. I agree that the ATSC
should have left it up to a choice. There is DTS, SDDS, and also MPEG with
more than 6 full bandwidth audio channels available. But because of wanting
to save bits Dolby's AC-3 was declared the audio standard for DTV. Not so
in other countries as I understand.

One other thing is that if everything is done in component then colr frame
problems are eliminated as in component there isn't any subcarrier to
contend with as the picture is in it's YUV components. Color frame only
occurs after encoding the image for NTSC.

Jim Mendrala
Real Image Technology, Inc.


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