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Tech Notes

Published by: Larry Bloomfield & Jim Mendrala

E-mail = or

April 6, 2000

Pre-NAB Edition

Tech Note - 054


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. To remove yourself from this list, send an E-mail to: in the subject place the word Remove. We now have over 645 subscribers & growing. Thanks to our regulars and welcome to the new folks. This is YOUR forum! The Tech Notes are posted and past issues available at: and


From the Publishers:

Both Jim and I will be at NAB-2000 from Sunday afternoon until Thursday afternoon. We hope some of you will look us up while there. We are staying at the Imperial Palace. Jim's schedule is eclectic. I will be at the LVCC all days save Tuesday, when I'll be at the Sands.

Please call us on our cell phones if you'd like to touch base: Jim's cell is 661-609-5299 and mine is 408-202-0482.

You can recognize Jim by his picture on his personal web page:

You can see my picture in Broadcast Engineering at the beginning under Beyond the Headlines or if you see a fat guy in an electric cart, that's probably me.


Reader Feedback:

From: Matthew Sheby

RE: Tech Note #52

Tell me about it. I think I was the only non-Napa college guy in the audience. [And yeah, with the exception of the Firewire guy, the majority of the speakers were almost as exciting as test tones.]-Matt


From: Ted Small, Chief Engineer, KFXK-TV

RE: Tech Note #53

Prior to leaving for NAB I thought you would be interested in an update on the machine with so many hours. A few weeks ago Hugh Peavy, my assistant Chief, and myself went to Dallas to a JVC lunch / demonstration of Upconverting our 50mbs bit stream to HD using a Leitch decoder/encoder. All I can say is: WOW!

The Head life of our BRD-50 is 14,724 Hrs. We are getting a Brand New BRD-50 in exchange for this one. JVC wants to show it off at NAB. The bad news is today we pulled the machine off-line to replace the Head cleaning apparatus, and went to play an older tape and we had a first light indication of data errors. The tape in the shop had been around the block quite a few times, so we got a fresh one out of the library and it had a airable picture, but it to was showing first light data errors (data errors lights are three in number and go left to right). So if it were not for the new machine being on the way we would be installing our first head and drum replacement on this machine. It will ship out Monday April 3rd so the final number may hit 14,750 after this weekend. I thought you might, might want to pass it along. Thanks -Ted


From: C. B. Patel

Re: TECH NOTE # 52 & 53

These two Tech Notes are very interesting. I have followed this VSB-COFDM debate. We all read about the VSB receivers failing to perform in test after test. The Sinclair demo to the several Congressmen is only another example of it.

So far no one has bothered to analyze "why the receiver failed to perform." I have talked to my friend Chris Strolle at the NxtWave, Tianmin Liu at the Broadcom and Frank Eory at the Motorola. All these companies, so called the CHIP-Manufacturers are burdened to solve the VSB problems.

I have worked in the TV design at Sarnoff and then at Samsung since 1974. Unfortunately currently I am not with any TV design company. I work as consultant for Samsung but I do not have direct input in their TV designs.

From what I analyze, the problem is in front-end system design. The chip manufacturers are no experts in the front-end system design. Yes, they do provide an Evaluation Board so one can see their chip do equalization and VSB demodulation. But by no means their implementation is what is necessary for a good receiver design.

Unfortunately only that is available for Sinclair, MSTV and others for VSB testing. No wonder when their implementation is put to tests, it fails miserably. But still no one is asking them (Motorola, NxtWave) why did your system failed. No one is bothering to analyze the failure. Rather massive data is collected in number of sites tested.

If I were the designer, I need only one, the first site to fail for me. I must camp there, analyze the received signals, what is being processed in my implementation and understand thoroughly why it is failing. Failing even at one site, is one too many.

Do corrections or come to the conclusion that needed corrections are not possible before embarking on any more tests. But the Lab & Filed testing frenzy has gone crazy. The people who supposed to be doing the testing are not doing the tests. Whether proper design is done is never questioned. Unfortunately the chip-manufacturers are afraid to admit that certain area of the front-end design is not their expertise and want to claim their equalizer could do miracles, which is impossible. But they do not seem to understand the limitations.

What I am saying is "it is not the VSB that is failing, its (poor) implementation is failing." And if the results are properly analyzed or even looked at, it could be very easy to see that. But the issue is now politicized.

I am not saying that the COFDM is not better. But if the designer understands what a COFDM receiver does in their front-end so it does demodulate properly even in multipaths, and compare if any such "care" is taken in a VSB receiver design, it is not hard to understand why the VSB receivers perform the way they are performing.

You said that NBC/RCA came up with the needed correct solution about Color TV when needed. (Something like that). Unfortunately today, there is no such R&D Lab like Sarnoff of those days. Today's Sarnoff is not the same.

Where is the General when we need him? C. B. Patel


From: THOMAS LENTO, Sarnoff Labs

Subj: Re: TECH NOTE #53

I'm not getting involved in the 8VSB wars other than to point to our position paper on our web site.

But here's a thought for you on another of your points: the commercial justification for DTV.

In 2 to 4 Mbps of bandwidth you can push a raft of info and entertainment (read: music and TV-quality video) services through the air. Our WaveXpress venture is just one of the companies expecting to give broadcasters a whole new revenue stream that we think makes the DTV transition a good commercial move.

Naturally we think WaveXpress is the leader here, with their open business model and turnkey service.

By the way, at 2 to 4 Mbps for these datacasting services you still have room in a 6 MHz channel for an HDTV program or multiple SDTV programs using 8VSB. It's quite a bit tighter with COFDM.

Check out WaveXpress at NAB. Let me know if you want to talk to them and I'll see what I can arrange.

Also, on 1080i vs. 720p: Why don't people look at the ATSC standard? There is a "1080p" format built in, at 24 fps (native movie speed, no pull-down necessary). That's "true HD" with a 2 Megapixel picture no matter who's looking at it.

As for 1080i, though I'm not technical, I like to think of it as a placeholder for progressive-scan 30fps until compression technology improves. The ATSC standard is extensible, and there's no reason that can't be added when it's technically feasible. So locking into 720p for production and broadcast may not play so well, say, 5 years from now.



Subject: Encryption Systems for Digital Cinema

by Jim Mendrala

Digital cinema being discussed mainly in Hollywood seems to always bring up the subject of security otherwise known as encryption and de-encryption. It seems like a great amount of time and effort is being spent on security issues that have no real impact on the quality of the presentation. Any encryption system used in digital cinema would be transparent to the images and sound but would not sacrifice the security of the copyrighted material.

Based on the use of strong encryption systems and by the general inaccessibility of the entertainment content to the general public, pirated copying could result in movies being put on DVD-R. Standard Definition Television (SDTV) video versions of the copyrighted material could also be distributed on VHS or even on the Internet in violation of copyrights.

The attributes of an appropriate digital cinema encryption systems need to be explained however to the content owners, producers, studios, distributors and stakeholders. Even though sufficiently strong encryption is readily available today, the limited breaking of the DVD CSS (which was intended only to protect against casual copying) and the well-publicized hacker attacks on the Internet give the impression that encrypted content is vulnerable to code cracking. The reality is that essentially unbreakable content protection ciphers are available, and that secure access management systems can be assembled from thoroughly tested components. These statements remain true; even though logos and trailers may give crackers plain text versions of the cipher text they would attack. Security of protected digital cinema content will be far superior to that of today's 35mm film, but the problems of employee trust and physical security of the exhibition environment will still remain as points of vulnerability. Security experts understand that compromising modern encryption systems is impractical without accomplices among trusted personnel.

From the standpoint of digital cinema, the encryption systems are envisioned to have certain characteristics, including:

* A store-and-forward means of distributing the protected property.

This means that entertainment material will be stored and transferred between storage locations outside of the physical control of content owners (as it is with 35mm film) and there may be multiple stages of store-and-forward.

* The storage and distribution of the protected property will take place in hostile environments, which have no security by trusted personnel.

This implies a requirement for physical security of the digital cinema equipment, e.g., anti tampering provisions. Un-trusted personnel who may not be technically sophisticated will manage the exhibition of protected property.

To meet the requirements of presentation, the exhibition of protected property will be scheduled in combination with other protected or unprotected material by the exhibitor. The exhibition of protected property may be stopped for various reasons, and must be able to be re-started in a reasonable way.

Time based requirements for protecting property -- Owners of property to be protected are concerned about security breaches that compromise day and date releases (worldwide). Upon public exhibition, entertainment material is subject to copying by camcorders of various levels of sophistication. This form of copying takes place outside the encryption system, except for watermarking and fingerprinting protections, which imply legal protection sanctions.

The nature of the protected property contains image, audio, and metadata. It may also contain various other data, which might be essential for its presentation.

Protected property may also refer to information concerning the exhibition of the entertainment content itself. The ownership of such data is determined by the contractual agreements between property owners and stakeholders.

Functional requirements of the encryption systems for protected property owners and stake holders -- Stake holders are those parties who do not actually own the property but who have an interest in protecting it, at least in part. The encryption system must embody the contractual relationships between stakeholders and owners of the protected property.

Security -- Security is the first concern of the encryption system. It includes confidentiality, meaning the concealment of protected property from all but parties authorized to reveal, transport, or sub authorize other parties, according to their contracts with protected property owners. Security may also include means of tracking security breaches within or outside of the encryption system.

Authentication -- The parties using the protected property must be assured of the true identity of other transacting parties or equipment.

Data integrity -- The parties using the protected property must be assured that unauthorized parties have not modified the protected property.

Non-repudiation -- Transacting parties must be able to demonstrate that the sender and receiver did actually send and receive the claimed components of the transaction.

Availability -- The encryption system must ensure a quality of service that meets the contractual obligations of the parties. In addition to a reference to delivering exhibition, this requirement includes the ability to service equipment or maintain the encryption system with minimal impact on security or exhibition.

Specifics -- The encryption system must include among its protections authorizations, which apply to place, time, and exhibition equipment.

Renewability -- In the event that security is breached, the encryption system must be able to revoke compromised trust relationships (with hardware, software, or humans), report the security breach to responsible parties, and maintain security and functionality of the un-compromised components of the greater encryption system.

Co-existence -- Digital cinema encryption systems, like other elements of digital cinema, will co-exist for many years with the systems that now support 35mm film projection. Such legacy systems include the physical environment and personnel, existing automation systems, existing theatre management systems, and existing box office systems.

Press, employee, and test screenings -- Producers as well as exhibitors require presentations prior to opening day public screenings. The content protection system must apply to these screenings as well. One possibility for additional protection would be the inclusion of an obvious watermark, perhaps similar to watermarks as used by television stations, for these screenings. This watermark would not appear if certain access keys were used, and these keys could be time enabled.

Small market size -- The market size for digital cinema systems, certainly at first, is small compared to the size of encryption systems such in DirecTV or the Dish Network, for example. This suggests that the components of digital cinema encryption systems should be selected from existing, standardized hardware and software in order to keep costs manageable.

To add to the complexity producers and exhibitors so far have expressed the desire for the choice of hardware, software, and services to be open and competitive. This implies that the elements of the encryption system must be modular and interchangeable to some degree. It also implies the standardization of the interfaces between the various elements of the encryption systems. SMPTE is studying these issues in the digital cinema DC28 Study Group.

These are some of the concerns surrounding digital cinema. In the beginning back in June of 1999, George Lucas released "Star Wars - The Phantom Menace" to 4 theaters in the United States. At that time the only security used was a security guard in each of the projection booths. That was a humble start but security issues discussions have come a long way since then.



Subj: The following is in response to a letter from Robin Rowe, a new subscriber.

By: Larry Bloomfield

Re: Tech Note #53

I'm more than happy to answer your questions. When I said: "Although the ATSC technically classifies 720 lines as high definition, true HDTV is 1080 lines," I was referring to the international definition of HDTV and the ATSC. Tony (can't remember his last name) at ABC is heading the US International delegation to get 720P accepted internationally as HDTV. I've heard no word on the progress.

You said: "Under your theory neither 1080i or 720p would qualify as HDTV, although you later state that 1080i is HDTV." The actual frame resolution of 1080i is only half of that, or 540 lines at 60 fields. Granted it's a different 540 lines on alternate fields, but as I recall subjective viewers differ on whether 1080i or 720p is actually sharper. There are no fields with 720p as it is progressive.

In theory, I agree with your statement. I have been a proponent of 720P asking the question, "how can you take two different pictures from different points in time and expect them to look as good as a progressively scanned picture."

And yes, both formats have approximately the same bit rate. I have seen both 1080i and 720p side by side, and they both look good. If I was forced to choose, I opt for the 720p because of my bias. It is interesting to note that a new company is on the news front, iBeam and the group owners of the stations who subscribe and support it will go to 720p irrespective of their network affiliation - NBC or CBS.

When you said: "Motion picture resolution isn't just pixels," I agree. I used a Kodak statement in the SMPTE journal as my source for the comparison, which is their info.

I even went further then saying that HDTV provides wide-screen picture quality similar to 35mm film. I said that the D-Cinema in use to day is lesser quality than the broadcasters are transmitting. The TI system puts about 1.3 Megapixels on the screen. You do the math: 1920 x 1080.

That wasn't going too far. There are too many who say that is just fine and don't wish to push the limits to what we could have in the electronic motion picture technology. I saw Toy Story 2 all in digital from start to finish, never on film, in San Francisco as part of the Feb. 2000 SMPTE conference. I was impressed. There are many points, which made it better than a 35mm film presentation, but it is not the best we could have today. There are no standards establish, as yet, for D-Cinema. I hope and pray those who are establishing them at this time don't settle for anything but the best. We have the technology; let's use it.

As for my roll and interest in all this, I suggest you check out my bio at Mendrala's is there also. If you have any questions after that, I'd be more than happy to answer them. As for what I do, I know write and am a consultant to several firms. I had an accident several years ago that will only permit me to do that now. I've been doing Beyond the Headlines for Broadcast Engineering for nearly 2½ years. The folks at BE saw some of my early work in the Tech Notes and like it. The rest is history. In addition to this, I like to stir the pot. It never hurts to have a protagonist who is not afraid to take the bit in their teeth and get people to thinking. I know doing that, sometime, upsets people, but oh well. A person gets sore when they don't use mussels, which haven't been used for a while. The same is true of the brain. I'm never afraid to answer questions, as that tends to either make me rethink issues and either come up with a better way/answer or confirm my thinking. My best regards, Larry


Subj: ATM and video

From: Ralph P. Manfredo

(Ed Note: Manfredo is the President & CEO of BroadBand Networks Company in Santa Clara, CA. Manfredo is also in the process of writing a book on this very topic.)

What are these new terms or acronyms used in the digital television industry:



These acronyms are not Italian and I will try to explain them to you:

CBR - Constant (or Continuous) Bit Rate. This is one of the ATM service types offered in which a virtual circuit is configured to support a fixed (constant) amount of end system traffic for the duration of the connection. These services guarantee a fixed rate of communications

VBR - Variable Bit Rate. This is one of the ATM service types offered in which a virtual circuit is configured to supports the transport of "bursty" type of traffic as opposed to CBR traffic. VBR is characterized by an average SCR (Sustainable Cell Rate) and PCR (Peak Cell Rate).

ABR - Available Bit Rate. This is one of the ATM service types offered in which a virtual circuit is configured to provide a minimum bit rate for user transmission and allows a higher bit rate, up to PCR (Peak Cell Rate) if the capacity is available.

VPI/VCI - Virtual Path Identifier/Virtual Channel Identifier. The combination of VPI and VCI used to identify a specific segment of an end-to-end ATM virtual circuit (VC) between two ATM devices and to switch cells in an ATM network. (See VPI and VCI below.)

VPI - Virtual Path Identifier. A value in an ATM cell header that identifies the virtual path (VP) to which the cell belongs. This field is 8-bits in cells traversing a UNI (User-Network Interface) and 12-bits in cells traversing network circuits.

VCI - Virtual Channel Identifier. A 16-bit value in the ATM cell header that provides a unique identifier for the virtual channel (VC) within a virtual path (VP) on a given virtual circuit that carries that particular cell.

DSL - Digital Subscriber Line. General name for several specifications supporting digital customer local loops. See ADSL and VDSL below.

ADSL - Asymmetric Digital Subscriber Line. An ANSI standard that provides for voice plus a data connection on the same customer local loops that currently only support one analog voice connection. The data connection supports from 384Kbps up to 8Mbps downstream (to the customer) and 64Kbps up to 1.5Mbps upstream (from the customer to the network).

VDSL - Very high-bit-rate Digital Subscriber Line. A new and emerging specification to provide connectivity and broadband services to residential customers. VDSL supports from 27Mbps up to 52Mbps downstream (to the customer) and up to 3Mbps upstream (from the customer to the network).

FSAN - Full Service Access Network. This is a new and emerging standard being developed by the major telephone companies in the world. This standard will define how new DSL services will be distributed to the residence. There is an organization called FSAN and among its members are: Bell Canada, British Telecom, Deutch Telecom, French Telecom, GTE, Korea Telecom, SwissCom, Telstra & Telecom Italia (CSELT), SigTel (Singapore Telecom), SBC Communications, Bell South, U.S. West and GTE.

DSLAM - DSL Access Multiplexer. The network half of the DSL system. It can reside either in the central office (CO) or on the street. It concentrates multiple subscribers and provides access to the appropriate data services such as Internet Service Providers (ISP).

HFC - Hybrid Fiber Coax. A residential access technology to provide broadband services over the cable TV infrastructure with fiber to the curb and coax to the residence. Connectivity supports data rates of 27Mbps downstream and up to 1.5Mbps upstream.

FTTC - Fiber To The Curb. A residential access technology to provide broadband services over fiber optic cable directly to the home. This connectivity supports data rates of up to 622Mbps.

ATM - Asynchronous Transfer Mode. A broadband switching and multiplexing technology used for transferring video, data and voice information. ATM is a connection-oriented high-performance integrated technology that supports Broadband Integrated Services Digital Network (B-ISDN) services under specified Quality of Service (QoS) guarantees. Since capacity is allocated on demand with no clocking control between end points, is called asynchronous. Information is transmitted a very high rates using a fixed cell size. Each ATM cell is 53-octet (byte) packet comprised of a 5-octet header and 48-octet payload. ATM provides for different QoS Classes, allowing for traffic streams to be distinguished, based on Class of Service.

ATM25 - A version of ATM that uses CAT3 or CAT5 UTP (unshielded twisted pair) cable for use inside a building. The typical interface supports 25Mbps and uses the ATM protocol. The FSAN VDSL protocol appears to be leaning towards the ATM protocol because current VDSL products that are non-proprietary in nature are using ATM as the protocol. The set top boxes we used in both Korea and Canada had ATM VPI/VCI addressing.

Hope this helps.    Ralph


(Ed 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.

SUBJECT: NAB2000 and SCRI Research News

FROM: Des Chaskelson, Director, SCRI International

NAB2000 exhibitor listing and press release site - free access at: -- includes over 600 NAB2000 exhibitor listings and news releases! Contact for details. SCRI Research News:

US TV Station Migration to H/DTV -- System Specification

SCRI's New - 2002 Broadcast | Pro Video Trends Survey Now Online - Facilities only - Get FREE Access to Online Insider Report:

New HDTV Marketplace Trends Report: 2000 - 2004


The Tech Notes are published for broadcast professionals, and others, who are interested in DTV, HDTV, Electronic Cinema, 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 (419) 710-1913 or (419) 793-5283. 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 (including this message), 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.