Published by: Larry Bloomfield & Jim Mendrala
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Tech Note - 013
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Subj: Dolby Digital AC3
From: Larry Bloomfield
not necessarily East of Denver.
Our prime purpose here in the DTV Tech Notes
has always been to be a forum where we can present problems and
help find solutions. There is a major problem looming in the
not too distant future of HDTV. As we all know, the audio
will be Dolby Digital AC3. This is an encoded bit stream which
consists of 5.1 channels; specifically five full frequency range
channels; Right front, Center front, Left front, Right surround
(rear) and Left surround (rear) and one frequency limited channel
of sub-bass material. It sounds great but when it is encoded
as AC3 when it comes in on let say a network feed, it is not user
friendly at all! Like it or not, full frequency or not, before
the audio was encoded, that adds up to six channels of audio.
There are still many small market stations that have problems dealing
with "stereo" (2 channels) audio much less six.
Bring in the encoded AC3 on the network and
sending it, unmolested on through at the local station level, shouldn't
be a problem. Our question is what happens when it is necessary
to do a voice over, a promo over the close of a network show or
even more important when it is necessary to do an EAS? As
we see it, the local station will have to decode the AC3 back into
six channels add what they need to add and re-encode it.
Our questions are: Is there a simpler way
of doing it? How can we do our local audio business such as
inserts without screwing up the incoming signal? If you think about
it, we're sure you can thing of several more.
We're not Alone!
of Canada and South Korea have recently announced formal decisions
to adopt the ATSC Digital Television (DTV) Standard for digital
terrestrial television broadcasts in those countries, thus joining
the United States in mandating the ATSC Standard for such broadcasts.
Other counties are expected to join soon.
For more info, see:
Subj: Fwd: Faroudja Inc. To Deploy Prototype
Someone has gotta come out and say whether
the following is the "real thing" or just an HDTV technological
"cheat." To sum up what Faroudja is doing...
it's like the propeller manufacturers saying how they have designed
an even better prop for the B-36, when the B-47 jet was the obvious
Maybe Faroudja's next advanced technological
step is to buy CBS's color wheel patents, or an Edsel, i.e., "NTSC"
dealership! I hear Chrysler's auto turbine technology is on
the block too! (Ed Note: Don't sell your CBS color wheel
stock. Texas Instruments is using a color wheel with their
DMD projections system.)
Inc. To Deploy Prototype Upconverters Next...
To Deploy Prototype Upconverters Next Month; Revolutionary Delivery
of HDTV-Quality Images From Conventional Broadcast Sources
(Ed note: When I saw this same press
release, I contacted Faroudja and could not get them to comment.
I did, however speak with Snell-Willcox who also has an Up Converter.
The results of that interview is in the Jan '98 issue of Broadcast
Engineering which will be out in a few days.
Subj: Sony's E-Cinema
(The following came from Bill Hogan.
It is about Larry Thorpe's talk at the STE. It originally was sent
out to an internet forum similar to this one for Telecine interested
folks. (STE is a Los Angeles based organization of Television Engineers.
The organization has been around for over 50 years and has made
many valuable contributions to the Television industry.) Since
E-Cinema and HDTV have many thing in common, it is presented here
for your information.)
to keep their foot in the door with tape machines,
primary business) has announced (publicly stated) that at
NAB they will show a prototype of a new uncompressed
HDTV VTR. This
open reel 1" machine that uses tape that costs
$1,000.00/HR. When the HDTV Standards
were announced at this time a year
ago Sony found
that they did not have a Modern VTR for Post Production.
had spent the effort on a 7 to 1 compressed format for
that fits on the back of Camcorder sized like a
will record the current HDTV digital standard of 1920 x
1080 at 60 (or 59.94) interlaced fields per
second. Also it was
announced that it would record full
bandwidth RGB (no transcoding) at
1920 x 1080 24 Frames per second PROGRESSIVE.
This is because when you
do the math
you find that the data rate is the same for the two
formats. (Ron Martin--are you listening?)
Yes, Sony recording at 24
Frames progressive. Bet you it will
also record 720 progressive too.
They also announced
they are going to make a 24 Frame progressive Field
camera for "Cinema"
shooting for going back to film for distribution.
The VTR is based
on their "D2" transport---OH NO!!!!!!!
Only catch is
that the VTR will not be available til "Some time in
1999" In the mean time D5 is gaining
a strong foothold in the market.
Bill Hogan firstname.lastname@example.org
Any Receiver to Dolby Digital; Vantas...
(The following is presented as the Dolby Digital
AC-3 will be used in conjunction with HDTV.)
Vantas, a Microtek company
based in Redondo Beach, CA announced the introduction of the first
digital surround processor/amplifiers that allow users to
play back Dolby Digital (AC-3) with any receiver. These products
were shown at the 1998 International Consumer Electronics
Show in Las Vegas. The majority of the more than
29 million Dolby Surround systems sold to date can not play back
5.1-channel Dolby Digital. Dolby Digital is a universal
standard found on DVD, laserdisc, and PC multimedia and will
migrate to DSS, HDTV and digital cable.
They showed two models
which will enable all Pro Logic and stereo home theater systems
to play back 5.1 channels of Dolby Digital encoded sources.
further information, contact Elliot Rubin, Director of Marketing,
at (310) 297-5720 or email@example.com
First Single-Chip Digital Television Video Decoder
American Laboratories, Inc. (PAVCAL) announced that it has
completed development of the world's first
low-cost single-chip device which will switch between any of the
eighteen different television formats, each suited to different
purposes. It will also have the capability of addressing the
different screen ratios (16:9 'wide-screen' or 4:3), numbers of
horizontal and vertical lines of resolution, and scanning methods
(either 'interlaced' scanning, like today's TV displays, or 'progressive'
scanning, like computer monitors).
"This is the first single-chip device
that can decode and display all of the digital TV signals that can
be broadcast, using the new digital standard, in any of the different
HDTV or standard definition formats," said Sai Naimpally, PAVCAL
Vice President and leader of its DTV development team. "It
processes the digital signals in two ways, both decoding them for
display in their original format, and converting them for use in
termed a "Digital Television MPEG2 Main Profile at High Level
Video Decoder" -- functions in both a 'full-spec' mode and
a 'down-conversion' mode. In the full-spec mode, it decodes
the compressed video signal from the broadcast and outputs the original
format, that is, either HDTV (1080-lines interlaced or 720-lines
progressive) or SDTV (480-lines interlaced or 480-lines progressive).
Single chip operation is made possible by use of 500 MHz concurrent
16 Mbit Rambus(TM) DRAM's.
mode converts all compressed video signals to 480-interlaced and
480-progressive formats. This is accomplished by a memory-efficient
MPEG down-conversion algorithm developed by PAVCAL.
of the decoder chip conforms to both the DTV Broadcast Standard
adopted by the Federal Communications Commission and the more-detailed
ATSC DTV Standard, drafted by the all-industry Advanced Television
Systems Committee (ATSC).
(Ed note: Additional information and
diagrams will also be in my column in Broadcast Engineering's Jan.
'98 issue LB)
Subj: Sampling - a refresher
From: James Mendrala
We've seen different sampling rates batted
around. It wouldn't hurt to know the why and wherefore about
them. First you have to know where 4:2:2 came from.
As we all know, the frequency of the color subcarrier is 3,579,545.265
Hz. This is because the subcarrier has to be an odd harmonic of
the 4.5 MHz offset of the aural carrier from the visual carrier.
Otherwise severe morie between the two would look horrendous. In
order to take a composite color signal and sample it digitally you
need a little more than three samples per cycle of the 3.58 MHz
to satisfy Niquest's rule on sampling. if you take 4 samples of
the video you satisfy that requirement. So in order to do that you
need a sampling frequency 4 times the subcarrier frequency or 14,318,181
Hz. Along comes component. Since the bandwidth of the color difference
signals are half of the bandwidth of the luminance signal the term
4:2:2 comes into being. The Luminance is sampled at the 4 times
subcarrier and the color difference is sampled at 7,159090.5 Hz.
CCIR-601 standardized the frequency of the sample rate at 27 MHz
for both PAL and NTSC. that gives us a bout 720 samples per line
in both PAL and NTSC. (Since the frame rate in PAL is 25 fps the
longer time gives more lines vertically.) MPEG main level@main profile
calls for a 4:2:0 sampling.
what this means
is that the color difference is sampled at half the bandwidth horizontally
and half the number of scan lines vertically. MPEG-2 4:2:2 samples
like the numbers show. Full bandwidth for the luminance and half
the bandwidth for the two color difference signals. This MPEG-2
4:2:2 is new and will probably be the broadcasters SDTV format of
choice for DTV. If the video is sampled at a higher frequency it
is usually multiples of the 3.579545 MHz or there abouts. For example
the telecine that Advanced Video Designs, the HiRes 1440 samples
at 8:8:8 and outputs at 8:8:8, 8:4:4 or 8:2:2 so the video which
is over sampled looks good when re-sampled at Rec-601 clocks. In
theory a 8:8:8 video would have about 1440 lines of resolution double
that of NTSC's 720 lines.
Subj: On the move
Things change. Since our last issue,
I am no longer with KTVZ. Although I have gotten to love Central
Oregon, as soon as I find a new home for my talents, I anticipate
Since our last issue, I was contacted by Broadcast
Engineering and asked to write for them and get paid for it too.
This will not be a full time job, however. To put your mind
at ease and as you know, the DTV Tech Notes is a work of love and
none of us get paid for what we do here, nor do we ask nothing from
any of our subscribers except input. We want to keep it that
way. I have promised the folks at BE that I will not print
anything in here first if it is going to appear in their publication.
That's fair. By the same token, I will not use anything in
BE that you have provided us here, with out your permission.
I don't think there well be a problem telling you about things I've
run across that pertains to what we do here and refer you to it
in BE. The section that I'll be writing with be entitled:
"Behind the Headlines." It's been very exciting,
so far. In addition to those things Jim and I hope you share
with us for this publication, I hope you let me know if you have
anything you think, especially beyond the areas of DTV, HDTV etc.,
that might be of interest to the BE readers as well.
I am hoping that my new contacts will help provide information for
this venue as well.
(Ed note: Because of the similarities
of HDTV and Electronic Cinema, as mentioned earlier, we have included
this presentation for your information.)
by Jim Mendrala
(c) 1995, 1996,
1997 All rights reserved.
Electronic Cinema is being discussed and worked
on by several American and foreign companies. Theater goers,
in the not to distant future, will see bright, high resolution images
of at least 35mm quality, projected onto the big wide screen.
This idea of converting movies into a high-resolution, digital bit
stream (or packets of data) and delivering that bit stream to theaters
with quality as good as the film itself has the major motion picture
studios turning an eye towards the economic realities of electronic
distribution - Electronic Cinema.
Electronic Cinema can bring a number of important
advantages to the evolution of the film industry. First is
the amount of time and money saved, an especially important consideration
to the producer and/or distributor. Second, Electronic Cinema
can equal or better the very best cinema of today with its 35mm
or 70mm quality images. Technically, with today's technology,
there isn't any reason why film images (limited only by the film
itself) cannot be projected electronically onto the big screen.
Some believe that HDTV is the cinema of the
future. But HDTV has some inherent problems as we shall see.
Its resolution, though high, is only capable of super-16mm quality.
The incompatible frame rate, inadequate bandwidth, inadequate number
of scan lines, interlaced fields, and bandwidth limited color, all
combine to stymie efforts at real qualitative improvements in image
quality for the wide-screen cinema. The broadcast-imposed
standards of the television industry have tended to thwart the application
of a time- and money-saving video technology to a major field of
application - namely Electronic Cinema.
Today, movies are printed and the prints are
sent via land, sea, and air to the various theater chains.
Even though security is tight, piracy of the print to be shown does
happen. Prints for a typical movie are expensive. They
can average as much as $2700 per print copy. Prints also show
wear and tear. Prints get scratched and cinched. Prints
break and have to be spliced back together while the audience sits
and waits. Sometimes print reels inadvertently get shown out
of sequence. Also, when switching from one reel to another,
the film might be projected out of focus, sometimes for only a short
time, sometimes for the length of the whole reel.
In the near future, a whole new way of delivering
movies will evolve. Films today, with existing HDTV technology,
can be transformed into a digital signal using either the NHK 1125/60
HDTV system or the European 1250/50 HDTV system. With the
1125/60 HDTV system, the frame rate is 30 frames per second (fps).
This is not desirable, since film in the U.S. is shot and projected
at 24 fps.
The 1125/60 HDTV telecine must convert the
24 fps to 30 fps using the 3:2 pulldown technique. Not a very
good idea. Various digital compression schemes, such as MPEG,
have ways to look only at the actual 24 fps, thus freeing up some
of the time that would be wasted on compressing a video frame made
up of one field of the previous film frame and one field of the
next film frame. Sometimes the 3:2 pulldown detectors get
fooled. This is another reason why Electronic Cinema cannot
be led by conventional HDTV television technology that is being
advocated in this country.
The American Society of Cinematographers (ASC)
have insisted upon a 24 fps rate. With the European 1250/50 HDTV
system, the frame rate is 25 fps. This is closer to the 24
frame rate used in the U.S. and the one the (ASC) is insisting on.
Film in European and other 50 Hz countries is projected at 25 frames
per second. The difference between 24 and 25 is 4%.
With Electronic Cinema films can be shown at their original frame
rates, be it 24 fps or 25 fps.
Both of the above HDTV systems use a 2:1 interlace,
yet the film is scanned progressively and converted to interlaced
scan. The main reason for using the 2:1 interlace was primarily
to reduce flicker. Electronic Cinema progressively scans the
film. One major service bureau presently scans the film progressively
and generates a digital file for every frame, with a resolution
equal to or better than the film itself. We have seen the
results on the wide-screen in such films as Forest Gump, Apollo
13 and others. Those digital bit streams were put back on
film with no apparent loss of resolution even though they were manipulated
through various types of computers.
As you can see,
capturing a film digitally with quality as high as the film itself
is being done today.
Let's look at a typical film projector. The
projector has either a two or three blade shutter that allows each
frame to be displayed two or three times per frame. Thus,
what is seen on the screen is either a 48 or 72 picture-per-second
picture but at a 24 fps rate. Because of the light loss with
a 3 blade shutter most theaters use a two blade shutter. This
gives a picture a perceptible flicker that gets worse as the amount
of light is increased. Flicker tends to disappear when the
display rate approaches 60 fps. With today's digital technology,
to display a picture 2 or 3 times between frames is not a problem.
24 fps can be displayed at 72 (3x24) picture-per-second and 25 fps
can be displayed at 75 pictures-per-second, well above where flicker
tends to be perceptible. MPEG compression, in a way, does
this now when the 24 frame image is decompressed and it's output
displayed at 30 fps.
Most compression schemes are upward scalable.
This means that if MPEG, as an example, was used, it could be scaled
to do wide-screen, Electronic Cinema including scope-type films
with their 2.35:1 aspect ratio and beyond.
Today, when a producer or film studio transfers
a film to video, the process is very lengthy. A colorist does
a scene-by-scene color correction on the film. The film from
the film lab, as good as it is, is not as color correct as is required
in a HDTV viewing situation. After the scenes are color corrected,
the film is transferred into a digital signal and recorded.
Electronic Cinema would be no exception. A colorist would
be required here also. As a matter of fact, the only difference
is that the film would be observed on a large screen not some small
CRT type of monitor. Because of the CRT's phosphors, CRT's
cannot display as much color as the film image contains. New
projectors can display as much color as the film has. HDTV
has reduced resolution in the color. Equal resolution color
is a must for big wide-screens, something HDTV cannot deliver.
Lately, a new person has been added to the
list. A compressionist. Sometimes the colorist does
both functions and is known as a Compression/Colorist. That
person not only optimized the color but also the compression.
The main reason for the need of the compressionist is that today
films are destined for bandwidth-limited systems. A CD-ROM,
for example, cannot support the high data rates necessary for wide-screen,
high-resolution pictures. Even the new Digital Video Disk
(DVD) is only up to standard broadcast quality. The so called
"Sweet Spot" in MPEG encoding for professional broadcast
quality is around 6 MHz. For HDTV and wide-screen Electronic Cinema,
the data rates are much higher. Today, it is not only possible
to record that high amount of data with existing technology, but
it is possible to distribute that data by fiber optics or, more
economically, by satellite.
Today's satellites are designed for the traditional
data, communication, and television type of signals. Even
with today's satellites though, the much better Electronic Cinema
type of pictures are possible. In the near future, satellites
dedicated to Electronic Cinema movie distribution will be in place
to replace the current system of distribution.
Since the signal
is digital, no loss of quality would be visible to the moviegoer.
And because it is digital, various encryption schemes could be employed
to protect the feature from unauthorized exhibition or piracy.
Once the digital
bit stream reaches the theater, either via fiber optics or satellite,
it finally needs to be displayed.
Projection systems today fall into three main
categories, emissive, transmissive light valve, and reflected light
valve. Emissive displays are based upon cathode ray tubes
(CRT) or laser technology. CRT projectors today are relatively dim
and limited to approximately 1 KW power input. The best CRT
projectors give a maximum light output of approximately 1,000 lumens
at peak white. CRT projectors can suffer poor resolution in
the corners, spot growth at high beam currents, or visible line
structure at low beam currents. Laser CRT projectors offer
potentially higher power and more efficient operation but depend
on very low operating temperatures and the efficiency of the blue
lazing material is low. Laser projectors in general require mechanical
scanning and high power demands and potentially high costs.
Image speckle has been an obstacle in laser projectors even though
techniques can minimize this problem.
Until the Liquid Crystal Display (LCD) projector,
large screen projectors were based on electron beam addressed oil
films to produce high brightness projected images. These projectors
require continuous adjustment during their operating life.
LCD Projectors based upon transmissive active
matrix light valves, however, have efficiency losses due to polarization
and partial blocking of the light path by the active matrix.
They also deliver pixelized images, with low resolution, which is
inherent in their design. Image lag is also a problem on some
Reflective LCD light valves deliver, a very
bright, pixel-free image with more than 400% more contrast and much
higher resolution. The reflective LCD is addressed with a low level
infrared, high resolution CRT imaged onto a layer of liquid crystal
one for each of the tri-stimulus colors, RGB).
Digital Micromirror Device (DMD) projectors
are reflective also but unlike CRT's or reflective LCD's, use tiny
micro-size mirrors to reflect the light through a lens to the screen.
Pulse width modulation modulates the intensity of the light as seen
on the screen by the eye. This produces a linear modulation
or unity gamma (i.e., gamma = 1.0). A DMD device for each
of the primary colors (RGB) is used and being solid state, like
a CCD color camera, requires only a simple one-time registration.
Interlaced pictures are not suited to DMD devices, however, as only
half the maximum possible picture brightness would result.
By using progressive scan, the vertical spatial bandwidth is increased
by about 60%. DMDs are inherently low-flicker devices with
no lag. The DMD type of projector produces a picture which
is similar to projected film. The technology is scalable and
can provide aspect ratios of the projected image to include all
known aspect ratios, such as 2.35:1, 2.2:1, 1.85:1, 1.78:1 (HDTV
format), 1.66:1, and 1.33:1.
being developed today will evolve into a more efficient way of delivering
to the moviegoer a bright, sharp, excellent color, high resolution,
in focus, movie feature presentation with digital clarity and digital
CD quality multi-track surround sound audio.
The loss of prints en route to the theater
will be eliminated. Film breaks will be eliminated.
Scratched or cinch marked prints will be a thing of the past. Encrypting
of the digital data will make piracy extremely difficult.
Satellite delivery will make distribution costs plummet. All
solid state DMD type of projectors will make digital display of
the movie possible and relatively maintenance free, a real advantage
to the cineplex theaters of tomorrow.
Check out these
Subj: Some Closing Thoughts
technology is moving so fast that it is difficult, at best, to stay
up with things. I was once told that higher education teaches one
how to ask a better question. Working with today's technology certainly
is an education and, like you, I've got lots of questions. With
your help, we can find most of the answers.
digital video (601) comes with its own set of unique problems. It
would be great if, once encoded, we never had to convert back to
analog until we got to our final destination, the kinescope (picture
tube). How can we reasonably, and at the same time keep cost down,
approach this goal? There will be a whole new generation of equipment
on the market in the not too distant future. NAB will be, without
question, an education this year.
another area of interest. There are only a finite number of satellites
out there. No doubt there are more in cue to be launched and positioned.
It would be interesting to know what the demands will be in the
future for channel space on those highflying communications devices.
With compression we can get much more on a single bird, but with
multicasting, Hi-Defination, etc., the need will gobble up bandwidth
like a pack of sharks on a feeding frenzy. I often wonder if Dr.
Harold Rosen or any of the rest of my associates with Project Syncom
ever thought what we were doing back in 1963-64 would ever evolve
into this? We sure thought it was hot when we were able to tell
within three meters of where Syncom II & III were (at 22,300
miles) back in those days. I wonder how much more accurate they
deal of what is aired today originates on film. A producer must
look at how he is going to get his film turned into an electronic
signal with the greatest degree of fidelity. Will the target display
system be in a theater, someone's living room or on a computer screen?
Will the material be stored on tape, DVD or some, as yet undeveloped
media? The term telecine has almost totally disappeared at the local
level in this day and age and this is where the transfer must start.
There are several techniques of scanning the frames of the original.
The concept of film-to-tape transfer is becoming obsolete. There
is other storage media. What must take its place is the concept
of film-to-data transfer. It is only logical that Hi-Definition
television will demand that the thousands upon thousands of feet
of filmed material that exists as NTSC on tape today must be retransferred
to data with the highest possible rate of pixel capture our technology
can provide. This transfer process should only have to be done once
so that the any of several target destinations can be accommodated
-- theater, home entertainment such as DVD, a person's computer
or part of a broadcast.
move to digital television is a given. The timetable has been set
and now... the questions. These questions can be applied to both
local and network television, in very large towns to the smallest
of markets. Who is going to do what? The areas of primary concern
are Program sources and material. What changes need we make in our
approach to creative services in all areas, especially production
of commercials and public service messages? Can sales convince the
client the new way is better or necessary? What about News gathering
and presentation? Then there are the technical means of getting
all of this to the public. These are the most obvious issues. The
trick is to find the not- so-obvious issues, address them and find
person or company has all the answers, but together we can move
foreword like electronic Magellan's; circumnavigate this world of
digital television and bring, what was once thought to be flat,
into true global prospective. I would like to see the pages of this
part of Broadcast Engineering used as the navigational charts, wherein
we can share the hazards and routes to safely sail from one issue
to the next. Therefore, your input is most essential. Let me know
what you are up to and can share with the rest of us.
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
(541) 385-9115, (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.
--------- J_Mendrala@compuserve.com <<<<<
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