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 Some of the information may be out of date.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 (805) 294-1049
E-mail = <larrybend@aol.com> <J_Mendrala@compuserve.com >
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August 15, 1998
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DTV Tech Note - 020
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Sharing experiences, knowledge or anything else relating to DTV, HDTV etc. with your fellow engineers: That's what we are all about. We will send this to anyone asking, just E-mail us. If you are receiving this newsletter and didn't ask for it or want to get off the list, just e-mail us that request. Welcome to all the new subscribers. We hope everyone, new and long time subscribers, will participate in all ways with comment, experiences, questions and/or answers. This is YOUR forum!
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It's been 3 months since we put out the last issue of this forum. Hopefully it won't be that long till the next one. Thanks to the many subscribers who have e-mailed and called to find out what has happened to us. Remember that none of us who put this thing out get paid for our efforts and an income, sometimes, has to take priority. (Silly me!)
Many things have happened since our May 13th edition. If you will notice there is a new phone number in the masthead for yours truly. I'm sad to say that I no longer live in Central Oregon and will miss "the everything" about living there.
In addition to my continuing responsibilities at Broadcast Engineering (BE) magazine, I am now a training and publications coordinator for SunUp Design Systems, Inc., a software firm in San Jose. They are very much involved in television. It is their software that is the single point of control for multichannel television such as is used at DirecTV. I get to travel all over the world teaching our customers, such as Sky Latin America, DirecTV Japan, American Sky Broadcasting, and others, how our software makes their systems tick. Our Traffic and Control Systems software covers almost every facet of these operations and is some of the neatest stuff I've run across in my hour and a half in this business. It is a natural for those stations considering multichannel DTV operations or stations that are running multichannel operations such as SMA etc. I don't want this to be a commercial for them; I'm just trying to justify why we haven't gotten a newsletter out. I've had good intentions, but then my father once said: "the road to hell is paved with good intentions and you son, have a freeway started."
SunUp knows about both BE (I don't know how I'd ever be able to keep that a secret anyhow) and these Tech Notes and they don't have a problem with either. As long as I don't take a bite out of their time, they kind of encourage it. If you are ever in the Bay Area, San Jose (North) to be more specific, stop by the office and say hi. We're at 181 Metro Dr. Suite 600. I can throw a rock and hit the San Jose airport and we're next to US 101. Call first to make sure I'm not in Mexico, Miami, Phoenix, Jakarta, Japan, Rio, etc. on a teaching trip. The office number is (408) 437-4500 ext. 271.
As you can probably guess, the folks at SunUp think I can write, so that's where the "publications" part of my moniker comes in. I get to help write the users manuals. Having used many of those things, both good and bad, I have some very strong ideas on how that should be done so that some Tech. trying to use the one I wrote won't include me in a litany fit only to come out of a sailors mouth.
To conclude this much longer than I had intended excuse and apology, if you have any questions about SunUp or what we do, give me a call. I'm more than happy to spend some time enlightening you. Now, to the business of DTV.
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Some DTV notes from Larry's desk.
Probably the most valuable real estate in your home today is the top of your TV set. VCRs, Satellite IRD (receivers), Cable TV converters, etc. Well here's another one from, of all people, Sencore (yes the local TV fix it store test equipment folks) have a new $4,000 DTV set-top box they have created for Mitsubishi (but it won't have the company's name on it). It's basically a test generator for retailers who want to demo HDTV (1080i) without necessarily having a TV station handy to get a signal from. According to a newsletter I get from Consumer Electronics, the "Device is basically a bit-bucket that plays swappable modules containing 60 min. of royalty-free HDTV video." New programming modules are to cost around $100 each. Deliveries are due in September, and Sharp also, is said to be interested. As I understand it, it is nothing more than an MPEG-2 bit stream server, priced at $4,000.
A newsletter I get said that Compaq's new Presario can record nearly an
hour of 19.3 Mbps streams on it's 8GB hard disk, and can stream these
Bits over FireWire to another device with an HDTV decoder. It even has
an MP@ML decoder and the storage go up to 3-5 hours of Bitstreams in
the 3-6 Mbps range. List price about $2,300. They said that with removable hard disk modules that are easy to find, but you pay a bit more for the packaging.
You can buy a 9GB SSA drive for $1,400, so with IEEE-1394 controllers will cost no more, perhaps quite a bit less as volumes go up. You would simply daisy chain the FireWire connectors to these modules. (I submitted a story to BE about FireWire for the September '98 edition. If it gets cut, I'll run it here, as it is most interesting. You can get more on FireWire at their web site www.firewire.org
One more comment on this: The Iomega Jaz II ($499) will let you swap out 2 GB modules that currently cost about $125 in single quantities...this would be sufficient for about 15 minutes of HDTV. Oh boy! The camel's nose is in the tent.
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Has anyone seen the information that is out about a new Glyph DigDAT multifunction tape drive for either real-time playback or high?
Speed backup of digital audio or video? A friend called me and was telling me about it. He said it is a "datagrade" recorder that can handle SDTV and HDTV streams, and faster than real-time backup and restore of those cheap hard disks. It's even cheaper than the SVHS tape machines we used at KTVZ for everything at an AMAZING $995 and it's a HDTV recorder?
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Subj: What standard do you want to broadcast in, 480p, 480i, 720p, 720i, 1080p, 1080i at 24, 30 or 60 fps (frames per second)?
From: Jim Mendrala
DTV will work in all these formats. The DTV standard approved by the ATSC disconnects the receiver from the transmission system. That means that if you are transmitting an MPEG-2 bit stream that originated on film the frame rate will be 24 fps. We all know that 24 fps will flicker
if it was displayed at 24 fps. In the motion picture theater the projector uses a two bladed shutter to give you two applications of light per frame or 48 images a second. (Some theaters have a 3 bladed
shutter giving 72 images per second but this is rare as the light output is only about a third.) The DTV receiver's decoder will recognize the fact that it is 24 fps but depending on the display type will be shown with reduced flicker or no flicker at all. This is true for all resolutions: 480, 720, and 1080.
How will this be accomplished? Lets take today's regular TV set as an example. It cannot accept any signal except an NTSC signal at 525i line, 30-fps ± .03 and 60 fields ± .06 per second. The set top box will receive all of the various combinations of resolution and frame rates that are transmitted and will convert them into an NTSC type of signal. How you ask? Well if you were looking at an HDTV program at 1080p/24-fps program the DTV receiver will down convert that bit stream into 24 full frame images per second. Because the TV will only work at 525i, 30 fps ±
0.03, 60 fields ± 0.06 the decoder will read out each frame and down convert the HDTVi or p image to a SDTV progressive image. To get the 60 fields that NTSC requires the output from each frame will be read out even lines first and odd lines second producing the fields required and
will be smart enough to put in a perfect 3:2 pull down to convert 24 ±0.03 fps to 30 ±0.06 fps.
Another DTV receiver tuned to the same program as above will receiver the same bit stream and because it has an HDTV type of display using the Texas Instruments (TI) Digital Micro Mirror Device (DMD) with Digital Light Processing (DLP) the image from the decoder will be down converted from 1080p to 480 x 640, 600 x 800 or 1280 x 1024 (unless TI comes out with a 1920 x 1080 DMD) and simply feed those image at 24 ± 0.03 fps and display that image digitally at about 5,000 pulses of light per second. There will be no flicker here at all since the eye cannot see flicker
above about 65 pulses per second. Putting it another way the image for one frame will be displayed approximately 9 times per frame for a 208 repetition rate per second. This is quite a bit faster than 30 fps with 60 fields display. Therefore there will be no need for 3:2 pull down.
In the case of a LCD display type of DTV receiver the decoder will receive the same HDTV 24 fps progressive scanned images and will just load the array with the image and display that for the full 1/24 of a second before changing to the next image. In other words the display will display the image until the next image is loaded into the array. The image is scanned into the frame store but is displayed as a static picture until the next image is ready. This is somewhat like a slide projector projecting slides at 24 slides per second with an instantaneous change to the next slide. The only changes to the image are those pixels that change. Again no flicker and no need for 3:2 pull
down.
Now lets use a DTV receiver with a flat plasma display. For the most part the images at 24 fps will be displayed similar to the LCD type of receiver described in the above paragraph. The image will be down converted and scanned in to the display's driver from the frame store.
What about SDTV at 480i on the above receivers? In the case of the set top box feeding the NTSC type of receiver all images will be decoded and down converted to 525i, 30 ± 0.03 fps, 60 fields ±0.06 and the old TV will have a very good quality video displayed on its CRT. Not HDTV but a reduced resolution image that will go to the SDTV's display. In the case of the DTV with the TI's DMD and DLP the image will be up-converted to fit the native array's pixels. Again the images coming in at 30-fps ±0.03, 60 field ±0.06 will be stored in a frame store as 30 fps ±0.03 progressive and will feed the DMD display at approximately 6 times per frame for an effective rate of 167 fps.
The same scenario also applies to other line and frame rates. As you can see the broadcaster will not have to concern himself about the DTV receivers. He knows that all DTV receivers/decoders will process the signal accordingly to what the display needs for a good picture.
At the present time there are only a few DTV receivers. Some are CRT based and will display either an SDTV signal or a HDTV signal at either 480, 720 or 1080 and some use other technology like the DMD, LCD or Plasma.
However since the broadcaster must feed his analog NTSC transmitter also, all programs if higher definition than SDTV will have to be down converted and all 24 fps video will have to be converted to 30 fps with 60 fields and 3:2 pull down. Images at 60 fps will be read out as 60 fields per second. Field one being all the odd lines and field two all the even lines.
The only other thing is that the broadcaster will have to decide on what aspect ratio he will want to transmit. In DTV any aspect ratio is possible and letter boxing will be at a minimum with the 16 x 9 displays. For the older NTSC TV's the solution will be for the set top box to determine how the image will fill the 4 x 3 screen. Letter boxing will be more pronounced on the older 4:3 type of displays.
In Conclusion, the DTV broadcaster can use anything listed in the famous "Table 3" but because of the old NTSC transmitters he will have to down convert everything to run at 29.97 fps and convert to 59.94 fields and convert 23.97 fps to 59.94 with extra 3:2 pull down inserted to make 29.97 fps. So 24, 30 and 60 frames per second will not be used in the beginning of DTV transmissions because the NTSC transmitter must interlace the 3.58 MHz NTSC color sub carrier with the sound carrier which is 4.2 MHz above the picture carrier to reduce the moiré that would occur otherwise. This is why the frame rate became 29.97 from its original 30-fps. (When Time Code came on the scene later this made Drop Frame Time Code a necessity. Drop Frame Time Code adjusts to the slower frame rate and still reads out the correct time.)
Lucent Technologies, Sarnoff/ Motorola, and others have developed such chip sets for the down conversion of HDTV transmissions to SDTV and NTSC type of signals. In the same way an HDTV telecine that scans the film at 2000 x 1000 the output can be down converted to the standard NTSC signal of 640 x 480. The only thing holding the broadcaster back from Non-Drop Frame Time Code and 24, 30, and 60-fps operation is the NTSC transmitter.
I hope this sheds some light on why the frame rates, progressive vs. interlace scan, and resolutions. They are all possible in DTV but the old NTSC transmitters will have to keep the frame rates at the old 23.97, 29.97 and 59.94 because of the 4.2 MHz aural carrier and down convert any image greater than SDTV to an SDTV resolution picture.
Jim
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Subj: A few more notes from Larry's desk pad. Thought you'd like to see some of this stuff.
What kind of Ears?
After much speculation, testing and press on the reception of DTV signals, it's nice to get some good reports. According to WGN (Chicago), they say that their tests showed a 96.4% reception success rate in their area, with DTV doing much BETTER than NTSC. This includes indoor reception, but "adjustment of the antenna was not always trivial."
Will there be sets to watch it on?
The early bird will get the worm -- maybe. If you can get a DTV receiver out into the showrooms by November 1st for the salesmen to peddle, you might just have a corner on the market. According to information I've received: Thomson, Toshiba and now it appears that neither Hitachi nor Philips will have DTV receivers available for sale by November 1, according to a recent Consumer Electronics newsletter. Like Thomson, however, most plan to have demo units in stores by that date.
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What are his "Stats?"
Ever been watching a sports program and wonder what a particular player's stats were and didn't want to wait for some errant director to flash them up on the screen You could even click on a performer to get a bio or the likes. ? Well that might not be too far down the road.
There was a recent announcement from a group called the Advanced Television Enhancement Forum (ATVEF, www.atvef.com) of protocols for what might be described as HTML for video. The group and its supporters are a pretty impressive bunch: CableLabs, CNN, DirecTV,
Disney, Intel, Microsoft, NBC, NCI (Network Computer), PBS, Sony, SunUp Design Systems, Tribune, Warner Bros., and, in a supporting role, Wink Communications.
According to an industry financial analyst and venture capitalist, who wishes to remain anonymous, "it will be impossible for any start-up not to support a standard from such a powerful series of market leaders." It would appear that the Advanced TV Forum has, trumped any competing technical innovations that may be in the pipeline.
It is apparent that, to remain competitive, purveyors of the electronic entertainment media have to continually improve and enhance what they have to offer the public.
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It's coming together!
- ABC and Fox have selected for their 45 Mbps feeds ABC will feed via satellite to their DTV stations and Fox, because there will initially be few DTV stations, will use fiber instead of satellite for network feed.
Or Is It?
- Prepare to stand by to get ready to come to a screeching halt. Remember the old schedule of dumping NTSC by 2006, changed to 2007 by Congress last year? Well, according to FCC chair William Kennard, it is "unclear if DTV penetration will reach 85-percent (Congress's magic number by 2006)."
- The Tauzin-Markey cable bill is wending its way through Congress without anything specific to DTV in it, though it does make reference to "any signal of a local TV broadcast station that is provided by the cable operator to any subscriber."
- British Sky Broadcasting will subsidize about half the cost to consumers of receiving equipment for its new digital service, scheduled to begin October 1. An antenna, receiver, and remote control will cost subscribers about $325 out of an actual $656. (LB note: You can buy a DirecTV/USSB IRD, dish etc. from Radio Shack for $200 now!)
- Snell & Wilcox are designing a test pattern for UK digital broadcasts. Will this be an old Druid Head Test pattern?
- The U.S. Court of Appeals in Washington has ruled on July 23 that mathematical formulas are patentable, as long as the result is something other than more math. The case involved mutual funds, but it should be equally applicable to video effects and compression algorithms.
- Acoustic Innovations, California Audio Technology, McIntosh Laboratories, Monster Cable, Phast, and Runco have formed CinemaForte, a marketing alliance for home theater stuff. They plan exhibits at the CEDIA (home-theater installers) show in New Orleans in September and at
the Consumer Electronics Show in Las Vegas in January, both based on 720p, with programming supplied by ABC.
- Paul Allen (Bill Gates' ex-partner) is buying almost all of Charter Communications, making him, personally, the seventh largest (in terms of subscribers) cable operator in the U.S. He's paying roughly $3,800 per subscriber, some 14 times the expected 1999 cash flow and about 50-
percent more than other recent cable deals.
- CBS, meanwhile, made a pullback FROM cable, selling the half of the CBS Eye on People channel to Discovery and dropping the "CBS" part of the name. "The days of the 70-million subscriber cable network are long gone," according to Jonathan Rodgers, president of Discovery Networks, explaining why the channel reaches only a potential 11 million households.
- The NAB told House Judiciary Committee members on July 31 that it favors amendments to the video competition bill that would force any satellite service providers offering local broadcasters to carry ALL full-power TV stations in the area -- no mention of DTV.
- About modifications to DVD players allowing them to view out-of- region disks (Sony's is the latest to be modified by Techtronics (www.techtronics.com), "little can be done technically to combat this," according to someone at Universal Studios Home Video."
- Macrovision (and affiliate Digimarc) are working with Philips on a digital "watermarking" system for DVD and other electronic delivery media.
- According to the Cable Ad Bureau, the total broadcast share of prime time has dropped from 71.6-percent in 1992 to 57.6-percent in 1998, with cable growing from 20.2 to 33.2 in the same period.
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Later Larry
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A closing note from Jim and Larry: Thanks for you patience in waiting for us to get this edition out. Please, if you have something to say or contribute, please do so. This is YOUR form or journal. If your company or organization has done something different or new in DTV, let us know. In the not too distant future, I hope to be able share with you some of the exciting things we are doing at SunUp Design Systems. Until I have a clear-cut direction on what I can and can not write about, it's best to not say anything. Larry & Jim
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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 (and yes Larry's e-mail is till the same) or land lines (408) 778-3412, (805) 294-1049 or fax at (805) 294-0705. News items, comments, opinions etc. are always welcome from our readers; letters may be edited for brevity, but usually not.
>>> larrybend@aol.com --------- J_Mendrala@compuserve.com <<<
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