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 Some of the information may be out of date.
**********************************************DTV Tech Notes
% Larry Bloomfield & Jim Mendrala
(408) 778-3412 or (661) 294-1049
E-mail = larrybend@aol.com or J_Mendrala@compuserve.com
May 17, 1999
DTV Tech Note - 029
The Post-NAB '99 Edition
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Published when any of us have something to share and it is sharing our experiences, knowledge or anything else relating to Electronic Cinema, DTV, HDTV, etc., with fellow engineers: That's what we are all about. We will send this directly to anyone asking, just E-mail us. There is no charge for this Newsletter and no one gets paid (sigh!). If you want to get off the list, just e-mail us that request. There is no "majordomo," automatic server; we administer this manually (also, sigh!). We hope everyone will participate in all ways with comments, experiences, questions and/or answers. This is YOUR forum! Past issues are available at: WWW.SCRI.COM. Welcome to all new subscribers. We're now over 270.
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Notice: The SMPTE Technical Conference #141 in NYC has a session titled, "Electronic Media Storage." They have issued a call for papers for anyone who would like to present at November (19-22) NYC Conference. The papers concern all aspects of media storage (servers for acquisition, edit, distribution, archive subsystems, browse severs, other). If you would like to present at SMPTE #141 please contact SMPTE directly at (914) 761-1100 for a presentation submission form. Abstracts are due by July 2. Ed Note: Sorry for the short notice.
***************************************************Subj: NAB'99 A Few Observations
By: Jim Mendrala
In this day and age, no one can go to NAB, see everything, and do it justice. The consensus is that four days of exhibits is both too much and not enough. If you add any of the seminars, the task is nearly impossible.
A new element to the audio and video was data. Many thought data as possibly the means that will cover the costs of the migration or move towards digital television. Concerns as to how the migration to DTV will be “paid for” were heard everywhere at NAB '99. Hardly a manufacturer or software company in attendance didn't have something to add to the confusion.
Bigger than ever, but still spread between two locations about a mile apart, the "who's who" in the industry were there with their wares spread out for all to view. The Latin expression “let the buyer beware” was and still is good advice.
There was hardly any analog equipment on display, but there was no end to the various versions of digital SDTV and HDTV cameras and VTRs. Panasonic, Hitachi, Ikegami, Sony, JVC and other manufacturers each had their little variances on the same kinds of product. Panasonic introduced their AJ-HDF3000 24 frame 1080p D-5 HD VTRs. Most manufacturers offered both digital and NTSC composite outputs and those capable of high definition had SDTV composite outputs as well.
Buy the way if you need to get rid of some of your old analog equipment, one company, DigiBid, will help you sell it off. They can be reached on the Internet at http://www.digibid.com.
I saw several "digital" switchers capable of the higher bit rates required for high definition. Hi-def switchers typically output 1.5 Gb/s. This is where MPEG compression really steps in to get the HDTV bit stream down to under 19.4 Mb/s for transmission. Some switchers even had two outputs in SDTV, one in the wide screen 16 x 9 format the other in SDTV 4 x 3 format.
An underlying theme seemed to be bandwidth management. To be able to transmit more than 8 SDTV channels within 6MHz through statistical multiplexers seemed to be the order of the day. Keeping the bit streams slim, trim and compressed without having to perform any operation or manipulation on the picture, sound or data seemed to be the vehicle of choice. Editing MPEG 2 bit streams with transitions such as lap dissolves and wipes of two MPEG-2 bit streams was demonstrated.
There was some digital test equipment for DTV on display, but not so much from the manufacturers that used to be “well known” from the analog days.
ViewGraphics, Inc. and Sencor in conjunction with Sarnoff were demonstrating a computer generated “Digital Test Pattern” that will most likely replace the obsolete color bar signal. It can also double as a character generator or a logo inserter.
Another thing that was very apparent were the number of companies who, just a year ago, wouldn't even consider speaking to each other, but are now partnering to get their products into DTV. The mix is certainly interesting. Hewlett Packard announced at a press conference that it would have a name change in the near future. Same high quality products but from a new division of Hewlett Packard. As of NAB the new name had not been picked out yet.
A few manufacturers were missing with their once famous products. Gone was RCA, which had just about everything in broadcasting. Grass Valley Group with their switchers and terminal equipment. IVC with their cameras and videotape machines. Where are they?
HDTV however was evident everywhere. A good percentage of the attendees thought the 16x9 flat panel displays were in high definition, even though they had only about 480 lines of resolution and were displaying SDTV signals.
There were a few interesting demo attempts at 3-dimensional stereographic TV. One scheme used a head display with two micro display devices (one display for each eye), another one had the traditional Polaroid glasses, and yet another one claimed 3-D with no glasses at all. The last one attempted to simulate 3-D by “modulating the depth of each pixel” and the use of carefully chosen shooting techniques. Let the viewer and buyer be………….
Most electronic projectors were either LCD or DMD. Hughes/JVC had their G-1000 projector and it looked pretty good for screens up to 20 feet according to the spokesperson in the booth. Barco had some 720p material being displayed that looked very good despite the fact that all of the high Lumen projectors did not have HDTV resolution or the 16 x 9 aspect ratio. Most DMD projectors had a 1024 x 760 display, with the promise of 1280 x 1024 later this year after InfoComm. JVC mentioned that they were working on a 1920 x 1080 D-ILA chip for the consumer television market. Texas Instruments, according to a few projector manufacturers, will also come out with a 1280 x 720 (16 x 9) DMD chip for use in home DTV sets sometime next year.
Divicom demonstrated 10 SDTV channels on one 6 MHz channel with bits to spare. They use a look-ahead strategy to tell the MPEG encoder when a difficult scene is coming up. NDS demonstrated their MPEG encoder and displayed the pictures on SDTV resolution flat panel plasma displays.
There were also a number of companies demonstrating the management of content or “Essence” as it is now called along with Metadata.
One other major issue brought up at NAB '99 was the first, open for all to see, scrimmage between 8-VSB (eight levels Vestigial SideBand) and COFDM (Coded Orthogonal Frequency-Division Multiplexing). Comments from some engineers spanned an interesting range of opinion. One Chief Engineer referred to the "lack-luster robustness of 8-VSB." Another said: "The sooner we switch to COFDM, the better." Still another said: "We're too far down the road with 8-VSB! We'll never change!" This one subject had as many different approaches as there were people.
It seems like NAB '99 will go down in history as the year of digital everything, except for me.
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Subj: A New Port for DTV Transmit Antennas
By: Larry Bloomfield
While navigating the byways of NAB '99, I chanced to see what, at first glance, looked like a very heavy duty VHF panel antenna element, that was missing its cover, looming high above a booth with the letters TCI prominently displayed. Thinking the wile cable company had ignominiously transgressed it bounds and gone into the antenna business, curiosity got the best of me, so I had to stop and ask. Glad I did!
In addition to this VHF antenna, Technology for Communications International - ergo TCI, had a most interesting antenna on display. It looked like a 24 inch diameter rocket casing with notches cut into its side exposing cavities with center fed slot elements, which could have been mistaken for modernistic door handles by any of the computer Geeks who were in attendance.
Named the DigitalPLUS, this wideband slot antenna and a companion product were designed to accommodate more than one UHF channel, eliminating the need for multiple antenna structures or draping antennas on one structure like you would tinsel on a Christmas tree. According to Gordon Sinclair, TCI's VP of antenna and structural engineering: "this antenna is designed for the broadcaster who must operate on two channels simultaneously, weather they are adjacent or widely separated." Sinclair added, "This antennas is capable of operating at any or all channels in the UHF band simultaneously."
With eight slot element spaced equal-distance around the cylindrical support structure, the transmit pattern is essentially circular. By arranging the placement of the slots on the support structure, other antenna patterns can be generated. This is particularly useful in markets like San Francisco where the preponderance of viewers is in every direction except west.
These kinds of antennas can be stacked to accommodate additional transmitters or higher power. The only limiting factor is the internal size of the structure itself where the transmission line would traverse to other segments.
Not being familiar with TCI - the antenna company, it is interesting to note that they've been around since 1968 helping the balance of trade by doing most of their business overseas and sporting a most impressive list of satisfied customers.
Television antennas aren't their only forte. One picture in their booth showed a most impressive "curtain" antenna they'd designed and installed for the Voice of America for VOA's HF worldwide broadcast service. For additional information catch their web site at: www.tcibr.com
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Subj: About the 8VSB vs. COFDM Debate
By: Walter C. Jamison, P.E. << waltj@jps.net >>
Thank you for publishing the DTV Tech Notes.
When I read the paragraph about the 8VSB vs COFDM debate I had a sense that I have been down that road before. I set up one of the first AM Stereo transmitters if not the first in the
Northwest, back in 83 as I remember. There were 4 systems and much confusion,
misinformation, threats of lawsuits involved to say nothing of the incompatibilities between systems. By the time it had all settled out and a standard was reluctantly agreed on, every one had lost interest, and many had lost a lot of money too. The AM Stereo fiasco was mostly the fault of the FCC not selecting a standard. There was also a "bad loser" involved that threatened lawsuits if his system was not chosen.
It would be a disaster to the broadcast industry if this was repeated with Digital Television/Data. This time the FCC has done their job, and we have a standard. The 8VSB system works. I setup, with help from an able crew and the manufacturer, the first DTV experimental transmitter in the West using an early prototype exciter and an adapted NTSC amplifier. I have since installed a commercial transmitter and antenna for DTV and participated in a field test program in the Seattle vicinity. I am now retired, but believe I am qualified to say that 8VSB works well, but won't suspend the laws of physics, nor will COFDM. Yes it does work with indoor antennas, a small corner reflector works better than rabbit ears for UHF.
Charlie Rhodes has written a column in the March 24 edition of "TV-Technology" titled "8-VSB vs. COFDM: Debate Refuses to go away(but Should)" in which he points out that COFDM transmitters would have to be 10 times more powerful than 8VSB transmitters to provide the same coverage. Anybody for 20 IOT's in a row?
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Subj: What's New In MPEG-2
By: Larry Bloomfield
One can not talk about compression in digital television without tripping over MPEG-2 at one point or another in the process. If you are a television engineer in or soon to be in any facet of digital television and are not familiar with MPEG-2, don't let any grass grow under your feet; learn about it! There are any number of good publications available which will explain, in detail, everything you'll ever need to know about MPEG-2. Tektronix, Inc. has an excellent 17-page publication (2AW-1061-1) entitled, MPEG-2 Fundamentals for Broadcast and Post-Production Engineers. Very well written, the material is presented and explained in this tidy little booklet in such a way as to both inform and be a good reference.
Once you've got a handle on MPEG-2 and a feel for its presence in digital television, you can appreciate the efforts of those organizations that have developed software to perform the same functions as hardware. To date, real time MPEG-2 compression using software can only be done with standard definition program material. The limiting factor is the bit rate handling abilities of the current generation of PCs that are being employed to perform the MPEG-2 encoding and compression operation.
Two companies have lead the way in the software approach to MPEG-2 encoding, Pixel Tools of Cupertino, CA and Ligos Technology of San Francisco, CA.
Pixel Tools is not only involved in Software Encoding, but offers repair utilities, stream analyzers and video stream manipulators. Particularly impressive are Pixel Tools abilities to demonstrate on a PC screen the complete MPEG-2 encoding process showing the vector relationships of the compressed material, what is being thrown away and other important aspects of the process. It is a really great learning tool.
Ligos offers single pass variable bitrate (VBR) encoding in real-time. The new capabilities give users the increase benefits of smaller file size at the same high-quality resolution or better picture quality at the equivalent constant bitrate (CBR) file size. With bandwidth a constant consideration, this approach will go a long way to improve bandwidth management.
Both Pixel Tools and Ligos are only on the brink of a software architecture industry that may well replace the more expensive hardware and give the video quality control artists an ability to make cleaner and clearer compressed pictures here-to-fore not possible. Representatives of both companies say that all formats of digital television can be accommodated, but not all in real time. As other supporting technologies improve in speed and bit handling capabilities, real time MPEG-2 compression in high definition will become a reality.
For additional information visit Ligos' web page at: www.ligos.com and
Pixel Tools web page at: www.pixeltools.com
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Subject: An Encoder Stress Pattern (ESP)
By: Jeremy Pollack <<jpollack@sarnoff.com>>
Encoder Stress Patterns (ESP)
Sarnoff offers a unique synthetically generated full-bandwidth 32-frame video test sequence, which we call the Encoder Stress Pattern (ESP). Sarnoff has been selling this ESP video test sequence on digital videotape, or as a computer digital graphics file sequence (latter, e.g., Exabyte, for use on Viewstore or DVF specialized video processing computers). Sarnoff's
ESP video test sequence is designed to dynamically stress and so test MPEG encoders, but is also suitable for a variety of similarly related applications. At NAB'99 Sarnoff showed our Encoder Stress Pattern "playing" from Viewgraphics' PCI PC/NT based SD board, as well as their similar brand new VideoPump HD version, both being able to input & output -full- bandwidth serial digital video, the latter being HD on a 1.5Gb/s SMPTE-292M SDI stream.
Sencore will now be bundling the Viewgraphics' VideoPump HD board with Sarnoff's ESP video test sequence in a low-cost PC-based rack mountable 'box' to be called, "HDTV Reference Signal Source", model HD292M. As bundled, the box will initially display the Sarnoff ESP video test sequence but, with software already written, the same PC-based box can be utilized
to display any graphics or characters the user may generate, e.g., with PhotoShop or PaintShop, in ".ras" file format. As such, one might call this a poor man's HD graphics /character display generator... also capable of displaying HD motion sequences in real time as well. Indeed, the
general idea is to encourage others to port additional applications to this box. In that regard, the HD292M being based on a PC/NT platform, it is then an "open architecture" type of system, so adaptable and very suitable for a wide variety of HD stills or motion video capture & display
applications. For TV stations' master control room, video studios or production suites, the HD292M could be used as a replacement for traditional still pattern generators (e.g., color bars) as, in digital video applications, motion video sequences are much more suitable, and so too more valuable.
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Subj: The Beginnings of an 8VSB Translator
By Larry Bloomfield
The first of anything is always a news item and when it is the first 8VSB translator, or repeater as they are sometimes called, it should come as a bit of good news to those who are very dependent on translator for their television reception.
Who uses translators, you ask? Over 25 percent of all television viewers in the state of Utah, and some adjoining areas, receive their television through one or more translators. The Beehive State claiming over 500 licensed translators to cover the areas the stations from their state capitol, Salt Lake City can not reach due to the terrain. Oregon has nearly that many and I'm sure other states come close to those numbers where mountains are the rule rather than the exception.
The manufacturer is an unusual source. Known for their test devices for television receivers, San Fernando Valley (California) based K Tech Telecom, has come up with a device that consists of an 8VSB receiver and an 8VSB modulator. The unit performs off the air reception of the desired terrestrially transmitted digital television signal, including high definition when available, resamples, equalizes and corrects for channel errors. The cleaned-up bitstream then remodulates an 8VSB carrier on the desired RF channel.
K Tech Telecom's Steve Kuh says: "The 'resampling' of all digital signals, including the HDTV terrestrial signals, is critical to maintain the signal integrity and combat the multipath interference present in even a moderately hilly terrain." He added, "The channel multipath interference is removed by the remodulator and a fresh copy of the 8-VSB signal is retransmitted by the repeater transmitter at the HDTV REMOD site."
The VSB-REMOD-100 is the first remodulator/translator of this type. Kuh says their company also has an MPEG2 bit stream spooler, an 8-VSB Reference Receiver and an 8-VSB Modulator. It would not be uncommon to see K Tech Telecom's equipment on the production lines of many digital TV set receiver manufacturer's production lines.
In all fairness, the VSB-REMOD-100 has not gone through the FCC type acceptance process as yet and still needs an appropriate ultra-linear power amplifier on its output. Kuh says he is looking for a company to partner with for the amplifier portion of the device. When these final, but all-important, details have been completed, there are many places where these, or similar type translators or repeaters, will be welcomed. The only step remaining in the translator equation is the selection of good quality, ultra-linear antennas and transmission line attached to the inputs and outputs of the device. It is only too obvious that something will have to take the place of all those analog translators that populate much of the country, sooner, later or by 2007.
For additional information, visit the company's Web site at www.ktechtelecom.com.
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Subj: Leitch FORCE
From: Kendall.Meddows >>Kendall.Meddows@Leitch.com<<
On May 26th, in Atlanta, Georgia at Atlanta's Ritz Carlton Buckhead, the NFL will unveil the Leitch FORCE video server system, with a custom touch-screen GUI, that it will soon use in every NFL stadium. The system will store and playback live "gameplay" and instant replay video for officials' use in reviewing calls. Got Questions? Contact either Leitch or the NFL.
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Subj: Goodbye to DTV Express and WHD-TV?
By Larry Bloomfield
NAB '99 brought to mind two issues that are sad, at best, to report. One is that the DTV Express has run its course and soon will be dismantled and the other is that WHD-TV, our digital television test facility, is soon to go away also.
Harris and PBS have done an outstanding job of quelling the ignorance of both technical and non-technical alike, dispelling miss-information and providing a "hands-on" opportunity, but the job is far from being over! Despite the small stipend charged the attendees of their various presentations, the information disseminated is priceless. Managers and craftsperson's, both technical and non-technical departed the sessions with information vital to the implementation of digital television. In the DTV Express's 40-city tour, they have only been able to touch a fraction of those who really need this kind of service and information.
Probably the most dangerous situation in not just television engineering, but in any situation, is when there is a preponderance of the participants who are, in all good faith, trying to forge ahead, but they don't have a clue as to where they are going or the goal is vague, at best. Even worse is that they most likely don't know that they don't know!
This whole migration to digital is a complete paradigm shift unequaled in the annals of our industry. Just think; all those familiar pieces of test equipment in your inventory; the ones that you have learned over the years to depend on, even down to the multimeter don't apply or work in the new digital plant -- Well, may be the multimeter is an exception, but that's all.
This scenario has been hammered home time and again. The source of this opinion comes from not only the responses to a number of surveys made available but from the folks who are actually on the road attempting to remove the sigma of ignorance. Folks like those involved in the DTV Express project, the Broadcast Engineering Winter training sessions and other such note-worth endeavors.
When one encounters information from manufacturers that is contrary to proven and sound engineering fact and practice, how is one to know? When there are people who seek to force their particular technological position down the industries' throat irrespective of it soundness or technical competency, what can one do? No one knows better that they don't have "the answers" than I. Miss-information abounds! God knows I wished I had the answers. There is one thing that is certain: when all else fails, the expression: "Go back to the drawing board" has a life-preserving ring to it. The application of fundamentals in our craft and the familiarization with the fundamentals of any and all other technologies that are attempting to merge with us is absolutely imperative.
DTV Express is still needed and will be needed until the last vestige of ignorance has been replaced with solid fact and information. Harris can not be expected to underwrite this project forever and the participants who have graciously loaned the project the various parts needed to make up a "typical" digital plant need to be acknowledged and or compensated. Our industry needs to do this before the government gets involved. We all know what happens if the government gets its hands on anything.
Instead of haggling over 8VSB vs. CODFM, interlace vs. progressive and 720 vs. 1080, we need to educate both the technical and managers types so that, perhaps, that most precious and rarest of events might occur, the "original idea." The idea which might lead us to a technological breakthrough which will help us all get back to the business of providing the public the best possible vehicle to watch what ever it is that happens to strike their fancy. The prolongation of the DTV Express project is certainly a step in this direction, but it's time for others to step up and do their share.
The same arguments apply to WHD-TV. We're not done until we're done! Many of the technical issues of digital television have not even come up much less been addressed. If we don't have some place to try things out, it's like telling the medical profession to come up with a cure for cancer while we shut down the laboratories. It just doesn't make sense! Let's get our collective heads back out where the sun does shine and may be we'll get it right!
Having taught junior college for over ten years, two things come to mind. First, you can lead a horse to water, but you can't make him drink; then may be the horse doesn't know that he's thirsty. The other is, I have learned that you should never try to teach a pig how to sing: for sure you'll annoy the pig and with out a doubt, you'll waist your time.
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Note: This is to notify all our readers that I am no longer associated with SunUp Design Systems in San Jose, CA. If you wish to contact me, please use the telephone number and e-mail address here in the DTV Tech Notes. Someone passed this on to me asked that I print it: Talent does what it can -- Genius does what it must. Larry Bloomfield
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The DTV Tech Notes are published for broadcast professionals who are interested in DTV, HDTV, etc., by Larry Bloomfield and Jim Mendrala. We can be reached by either e-mail or land lines (408) 778-3412, [note Jim's new area code] (661) 294-1049 or fax at (661) 294-0705. News items, comments, opinions, etc. are always welcome. Letters may be edited for brevity, but usually not.
>>> Larrybend@aol.com --------- J_Mendrala@compuserve.com <<<
DTV Tech Note articles may be reproduced in any form provided they are unaltered and credit is given to the DTV Tech Notes and the originating authors, when named.
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