-
Archived
Tech-Notes
Published by: Larry Bloomfield & Jim Mendrala
The following are our current e-mail addresses:
E-mail = hdtvguy@garlic.com
or J.Mendrala@ieee.org
We have copied the original Tech-Notes below as it
was sent out. Some of the information may be out of date.
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Tech
Notes
Published
by: Larry Bloomfield & Jim Mendrala
(408)
778-3412 or (661) 294-1049
E-mail
= larrybend@aol.com or J_Mendrala@compuserve.com
August
30, 1999
Tech
Note - 039
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Talent
does what it can, but genius does what it must!
Our Mission: Sharing experiences, knowledge,
observations, concerns, opinions or anything else relating to Electronic
Cinema, DTV, etc., with fellow engineers and readers. We do hope
that everyone will participate with comments, experiences, questions
and/or answers. The other stuff that used to be up here is
now at the end of this newsletter. We're growing. We
now have over 465 subscribers.
This is YOUR forum!
Past
issues are available at: WWW.SCRI.COM
**********************************************
(Editor's Note: Our Tech Note
#38 received the most reader response of any of our Tech Notes todate.
The following are representative of the e-mails we received.)
***
From: Ed Williams of PBS >>>
ewilliams@PBS.ORG <<<
About the Harris radio and TV Open House to be held at our new 165,000
square foot "Center of Excellence for Digital Technology"
in Greater Cincinnati, Oct 1. Ed said: "It is quite
a place. It opened on the same day the DTV Express arrived for it's
decommissioning. It's quite a place. It's a huge place. The DTV
Express Truck looked small in their "high bay" area. They
could handle 6 at once in there. They also have a special area for
operating several full size transmitters at the same time. The office
area is also designed for serious expansion - which, I suppose what
Harris has in mind. Big place! Go see it. Find an excuse."
Cheers, Ed Williams, PBS
For additional information and registration, call 800-622-0022
***
In response to
our Subj: A couple of questions
We raided the
possibility of a virus being introduced into a digital television
system or set top box. One reader, who works at one of the major
networks, said: "If the STB is only connected to a closed system
such as the program originator or cable system, it should be fairly
well protected from the outside world. Not immune from employee
malice, but pretty well protected. If the STB is connected to the
Web you could have protection similar to a corporate LAN firewall
that could filter known viruses.
"Concerning the DTV plant, we are already so reliant on Windows
and Macs that anything can happen. As your television becomes more
like your computer, you have to treat it more like a computer. Now
excuse me while I go do my daily backup on my STB."
Name withheld by request
***
Also in response
to our Subj: A couple of questions
Martin Caniff commented: "Thanks for bringing up the problem
with CBS's west coast feed to the satellite providers. I've noticed
the same problem -- and couldn't figure out the right place to lodge
my complaint." Regards, Martin Caniff >>>
martin@doctordesign.com <<<
***
Comments
from a well-respected San Francisco Bay area engineer
By: Roy Trumbull
The Dr. Yiyan Wu article is available from the ATSC site.
I found it interesting that the actual signal level penalty vs.
8VSB is far worse that the predicted penalty. COFDM certainly has
an advantage in areas of high multipath but it remains to be seen
how it does in an apple-to-apples comparison (same power level and
same bandwidth) on medium to far paths when the first Fresnel zone
is partially or completely obstructed.
For DTV reception, the bowtie array antenna is worth considering.
There are several ways to build it but it is essentially four stacked
bowties against a screen reflector. Quality is another matter.
Some antennas are built out of very flimsy brittle materials. I'm
trying to get a Lance bowtie array. Their antennas are heavy duty
and you can buy galvanized versions.
The GI encoder
is able to insert a watermark. As soon as I can get a file prepared
by our art department, we'll have one on the air.
Roy Trumbull
>>> roy547@email.msn.com <<<
**********************************************
In response to the story, "What will
it take," Dick Hobbs (DH) wrote us to which Jim Mendrala
(JM) responds. Mendrala's responses are in parenthesis after
each of Hobbs' paragraphs.
Mendrala says: (Thank you for writing in
with your comments. I have added my comments [in parenthesis] in
answer to your concerns. Electronic cinema is still in it's infancy
so many things will be looked at and redone if necessary.)
Hobbs said: "Larry and Jim wrote a
thought-provoking piece on electronic cinema, addressing the resolution
issues. However, I am not quite convinced that it analyzed the whole
story.
DH: It is true that the resolution of film is much higher
than any electronic medium yet developed. Most authorities suggest
that 35mm is capable of what we for convenience call 4k resolution,
i.e. there are about 4,096 pixel equivalents along a single horizontal
line. Because all film is made in exactly the same way up until
the moment when it is sliced and the perforations punched, 16mm
has proportionally fewer pixels per line, 70mm proportionally more.
(JM: This is true. Film has a grain structure
that is capable of resolving over 3,500 pixels. To scan that film
and convert those random film grains to a digital image requires,
like you say, 4,096 pixels in one horizontal line. Larger film formats
will require a higher pixel count to equal the larger area of the
larger film. By the same token, smaller film formats can get away
with lesser pixels because the area of the film is less.)
DH: But here is the interesting point. Although that is the
theoretical figure, in practice both amateur consumer eyeballs and
professional post-production systems are surprisingly tolerant of
much lower resolutions. Although in the first flush of digital film
excitement systems were built to 4k resolution they were almost
never used, with most people happy at 2k resolution (2,048 pixels
across a line of 35mm film, or barely more than HDTV). Astoundingly,
the dinosaurs in Jurassic Park were largely created and composited
at 1k resolution, i.e. lower than HDTV.
(JM: There are many reasons for doing 2K
(2,048) pixel scans. The main reason is cost and throughput. Cinesite
in Hollywood offers digital mastering for CGI. They take the 35mm
film and put it onto a "Spirit" telecine and do 2K scans.
The film is sampled by four 480 pixel sensors for a total of 1,920
pixels per horizontal line. The color is sub sampled at half that.
By doing 2K scans the throughput is around 4 frames per second at
this time on a "Spirit" Other scanners that do 4K scans
in use at the present take about 8 seconds per frame. That's about
30 times slower. Newer telecine machines are rumored to be closer
to real
time but won't be available for at least a year or more. Then there
is the problem of "pin registration". Film is exposed
in the camera after it has been registered. In order to reduce compression
pin registration has been shown to reduce the bit rate in MPEG systems
up to as much as 20%.)
In "Star Wars - The Phantom Menace" straight film shots
were reduced in resolution to match all the 2K EFX by also scanning
them at 2K. Interestingly if you are more than three screen heights
from the screen it is difficult to see the loss in resolution. No
problem in the home where people generally sit that far back but
a lot of theaters at three screen heights you are at the last row
in the auditorium.
If you get to the theater late and all the best seats are taken
you have to have the better resolution or you will be greatly disappointed.)
DH: The recent demonstrations of electronic cinema have used
either the Hughes light projector or the Texas Instruments DMD system.
I cannot speak for the Hughes, but the highest resolution TI chips
currently available have 1,280 pixels horizontally. Yet its projection
quality was considered directly comparable to 35mm film.
(JM: No, the quality from the TI and the Hughes-JVC is not
that good. What is considered directly comparable on the TI projector
is the color rendition and light output is comparable to 35mm film
through a standard projector i.e. 16 ft. Lamberts. Color because
it is RGB additive has a wider color gamut capability then the film
with white light.)
DH: My view is that, for purists, clearly there is much to
be done. But we should all be aware that there is a pragmatic view,
which is that we probably have enough resolution now. The advantage
of digital projection - a consistent quality, not related to how
many times a print has been shown and how badly it has been handled
- is worth achieving in itself.
(JM: We have enough resolution to start making money on it,
yes. But the other advantages are a real plus for the theater-goer.
Resolution will improve as projector technology improves. TI is
holding at 1280 x 1024. That is a computer standard and has an aspect
ratio of 1.25:1 which necessitates the need for special non-standard
transfers and different anamorphic lenses for the different aspect
ratios.)
DH: But I've only been talking about two dimensions of resolution.
It is depth that is the real problem: how do we store and move enough
bits to get a 1,000:1 contrast ratio?
(JM: 1,000:1 can be handled with 10 bits.
10 bits per color channel is equal to 1,024 levels of gray or a
wee bit more than 1,000:1.)
Dick Hobbs >>> Dick_Hobbs@compuserve.com <<<
**********************************************
Subj: New Digital Receiver Technology
from Motorola Enhances 8-VSB Reception, Solves Multipath Problems
By Frank Eory,
Designer, Digital Television Operations, Motorola
A new digital
receiver technology from Motorola solves a potentially serious reception
problem in digital and high-definition television (DTV/HDTV) broadcasts
that use the Advanced Television Systems Committee (ATSC) transmission.
Broadcasters
expressed concern recently when third-party test results showed
that multipath reflections interfered with DTV reception. Addressing
this issue, Motorola, in collaboration with Sarong Corporation,
created a new digital signal processing architecture and its first
implementation in the
MCT2100 demodulator and forward error correction
(FEC) chip. The chip uses proprietary algorithms and unique
equalization architecture, providing optimal signal reception even
for the most extreme static and dynamic multipath signal ensembles.
Motorola expects
that the new technology will make the broadcasting industry's efforts
towards ATSC a reality. Motorola combined its 0.18-micron CMOStechnology
with state-of-the-art signal processing algorithms to provide a
proven, low-cost solution.
Early implementations
of 8-VSB (vestigial side band) HDTV transmissions showed problems
in dynamic multipath and long-delay static multipath reception.
Motorola's new technology, MCT2100, compensates for a broad range
of dynamic echo ensembles with echo amplitudes approaching the level
of the desired signal. In static multipath with long delays, the
MCT2100 corrects ghosts with up to 41 microseconds of delay. It
achieves this bys incorporating a full equalizer design, which avoids
the sparse equalizer techniques that compromise performance.
Glenn Reitmeier,
Vice President for DTV and Web Media at Sarnoff, said the new chip
means that all of the capabilities of the ATSC standard will be
available to TV set makers and their customers, the viewers. "The
MCT2100 is a major step forward in implementing the perfect pictures
and reliable data transmissions that the creators of the ATSC standard
intended for DTV and HDTV."
The MCT2100 is
a member of Motorola's M-DTV(tm) chip set.
(Ed Note: We did not get an e-mail
address for Motorola's Mr. Eory. We will be more than happy
to pass on any inquiries through Motorola's PR firm who arranged
for this article.)
**********************************************
Subj: A Two Bit Stereo?
By: Larry Bloomfield
The connotation of a two bit anything is not
something most would relish, but when it applies to digital products,
the fewer bits to do the same job is usually better. If two
bits are good, then one bit should even be better. Such is
the case with core amplification technology developed by Sharp utilizing
7th order Delta-Sigma modulation with noise shaping and
an incredibly high speed switching circuit. In theory, reproduction,
under the most ideal of circumstances, is usually only at half the
sample rate. For example, if the sample rate is 1000 cycles,
the absolute best one could hope for would be 500 cycles, and even
that is wishful thinking. As the sample rate increases, expectations
for better quality reproduction improve. The Sharp 1 bit amplifier
circuit samples at a rate of 2.8224 MHz, allowing for sound reproduction
incredibly close to the original signal, with plenty of room left
over.
As we address the wonderful world of digital
television, we sometimes tend to forget that there is sound with
our pictures and with AC-3 breathing down our necks, we have 5.1
times as much to deal with as with old fashion monaural. Keeping
track of bits, audio or anything else, begins to be important in
the over all scheme of judicious bandwidth management.
There are some rather interesting benefits that
come with this one bit amplifier. Things like frequency response
of 5 Hz to 100 kHz, transient response of 2.8224 MHz, and a dynamic
range that approaches 110 dB in the audible range. Power consumption
is also a concern and the one bitter requires about half that of
traditional analog amplifiers. This reduces heat dissipation
to about 20% of it's analog cousin and all this requiring about
1/4 as much space and better use of the building's air conditioning
system. What makes this amplifier worth considering
is it rated power output of 100 watts plus 100 watts at 8 ohms.
The intellectual
properties associated with the 1-bit amplifier are covered by no
less that 58 patents filed by Sharp, including 12 that relate to
Analog/Digital conversion and DS
(Delta-Sigma) modulation. To this add 14 additional patents that
relate to applied audio technical conversion and 22 that relate
to playback and decoding technology. With that much invested
in that many patents it is obvious that Sharp plans to utilize this
technology to its' fullest. No mention was made by Sharp to
license this technology to other manufacturers, but don't be surprised
if they do.
One more note. Sharp has announced a CD
that will hold 40 two-hour movies. That's 80 hours on one
disk. Stay tuned.
For more information,
visit the Sharp web site at: www.sharp-usa.com
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Question: Does anyone know about the September
9, 1999 as being any special with computers? We've been told
that 9999 is a code that is commonly used in computers to shut programs
down. Your input is most appredciated.
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Note: The Editors and Publishers of the
Tech Notes wish to thank Des Chaskelson, Research Director of SCRI
International for his generosity in posting the Tech Notes on the
SCRI web site. www.SCRI.com
**********************************************
The
Tech Notes are published for broadcast professionals,
and others, who are interested in Electronic Cinema, DTV, etc.,
by Larry Bloomfield and Jim Mendrala. We can be reached by
either e-mail or land lines (408) 778-3412, (661) 294-1049 or fax
at (661) 294-0705. The Tech Notes are sent (BCC) directly
only to those who have asked to be on the mailing list, however
feel free to forward them, intact, to anyone who you think might
be interested. There is no charge for this Newsletter, no
one gets paid (sigh), there is no advertising and we do not indorse
any product or service(s). The ideas and opinions are those
of the individual authors. We still administer everything
manually. We don't use any "majordomo" automatic
servers. News items, comments, observations, opinions, etc., are
encouraged and always welcome. We publish when there is something
to share. Material may be edited for brevity, but usually
not. Tech Note articles may be reproduced in
any form provided they are unaltered and credit is given to both
Tech Notes and the originating authors, when named.
If they are to be used by a publication that normally compensates
their writers, please contact us first.
END
