Published by: Larry Bloomfield & Jim Mendrala
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Tech Note - 023
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Some DTV notes from Larry's
NDS has just
announced that they have digitally compressed four NTSC 480i
signals into a standard ATSC 19.39 Mbps channel.
In a separate test, NDS also
compressed one ATSC 1080i and one NTSC 480i signal into a signal
19.39 Mbps channel. In both instances they
overlaid these tests with the
Specific Information Protocol as spelled out in the ATSC specs.
in Broadcast Engineering on this subject.
Another tasty bit of info. EchoStar got
a really good deal. 2 more birds by
go up in 1999 on News Corporations dime, the A-Sky-B facility in
Ariz., a leg up on half a million set top IRDs, a three year deal
FOX net's O & O local-into-local plus the Fox News Channel on
Dish Network and an EchoStar/MCI telephone bundle
News deal. More to come.
OF 24 FRAME AND THE NEW 48s FRAME FORMAT
By: Jim Mendrala
The new ATSC
standard permits the transmission of basically 4 video
2 SDTV formats (4x3 and 16x9) and 2 HDTV formats (1080x1920 and
along with their respective variations of field per second
frames per second (fps). This seems to be creating an
scenario for the production and post production industry. In
the production and post production industries have delivered
in either NTSC, PAL, or component at either 30i fps or
With the introduction of DTV, the networks and independent
groups are specifying different formats. Some want 1080x1920
at 30i fps,
some want 720x1280 at 60p fps, and others want 480x640 at
and so on. This is creating an impossible financial and
burden on the production and post production industries.
to the problem has surfaced and a 24p fps mastering format in
has been proposed to simplify the process of converting to the
which the networks and broadcasters worldwide will
need in as short a time as is possible. It doesn't make sense
a film, for example, in HDTV then change the telecine to
then change the telecine again to output PAL, etc. Since
the new HDTV
and data scan Telecines are very expensive, a way to bring
down to a simpler format is required.
So on December
3, 1998, a SMPTE meeting was held at Sony Studios'
building to discuss what SMPTE can do to put some sense and
to the 24p fps recommendation, format conversions and
display devices were also discussed. The
proposed documents introduced
at the meeting
were finished in the shortest possible time ever for a
and feedback from the production and post production
is drastically needed. SMPTE would like to have several
practice documents in place by April of 1999, in time for
Association of Broadcasters), said Engineering Vice
William C. Miller.
manufacturers say they will be delivering 24p type of
after NAB '99, so producers will be able to start turning out
product by the start of the fall 1999 season.
been proposed is (1) a straight forward 24p fps video standard,
and (2) a
24p fps 48sF standard referred to as 48sF. The second idea has
because of the need for a shortened time that some
think they need in order to have product in time for the
season. Since a lot of equipment is now dealing with interlace
a modification to convert the operation to a slower field
be easy to do. But the desire is to have progressively
Progressively scanned images when run through an MPEG
cut the bit rate down anywhere from 25 to 35%. With
picture elements, motion vectors are easier to encode, and
frame rate is lower, there is more time per frame to do the
today all progressively scan film at 24 fps, the image
can be output
as 1080x1920 at 24p fps. Recorders to do this, while
have not been "invented" yet and will not be ready for
So to make
the 24p more compatible with today's interlaced equipment.
recommendation has been put forward, namely 48sF. In 48sF,
the 24p fps
image would be converted to two segmented images, with the
image composed of all the even lines of the
scanned frame, and the second segment all the odd lines of
frame. The images would be captured at 24p fps but would be
to 48 segmented frames.
presented by two of the equipment manufacturers is that 24p
does not exist yet so why not use 48sF to be able to get
ASAP, with minor or slight modifications to existing
So it is hoped that SMPTE can provide the common grounds and
of ideas to come up with a working solution.
is how a typical telecine transfer of a one hour
is handled in the Hollywood area.
In a typical
telecine suite, an average one hour movie requires
40 hours of actual telecine machine time. Due to reel
color correction considerations, a week is usually dedicated
to the production of just one Telecine Transfer Color Master.
second week, with more film handling required for the many
broadcast formats, Pan Scan, letterbox, anamorphic or
NTSC, PAL in 4x3 and 16x9, and HDTV in 16x9, are done for
PAL and HDTV distribution masters made from that Telecine
Color Master take anywhere up to 3 to 5 times the length of the
to simplify the process and make it more economical in the post
area, a simpler way has to be found.
24p fps seems
to be the format of choice. It is progressive. It is at
frame rate as the film. It compresses more efficiently than
Up to five SDTV channels can be transmitted at the same
time in the
DTV 6 MHz channel with plenty of room for other data
24p fps can
easily be up converted to a higher frame rate such as 72p,
60p or 30p.
Interlace can be introduced as well as 3:2 pull down. Time
code is the
same as the film and is non-drop frame.
24p fps can
also be played back at 25 fps for those countries that
24p fps can
become the universal standard of choice for all
are some problems that rear their ugly head. For example: How
do we monitor
24p fps. If you've ever watched a movie at 24 fps with a
shutter, the flicker would drive you nuts. 25p fps is no
how do you use 24p fps?
In the film
world, the use of a two-bladed shutter to reduce the flicker
about a hundred years ago and it tends to work. All movies
this technique. Viewing a movie at 24 fps with a three-bladed
better but more light is required. The flicker at 72 times a
To view a
24p fps video, the display device will display the frame in
1/24 of a
second and be updated in a very small amount of time to the
This is how some of the new micro-display products, used in
and the flat panel plasma displays work. The problem in
a CRT display
though is that the phosphor doesn't stay lit and has a
of x number of milliseconds. The phosphor needs to be
continuously. For a 24p fps video to have only a small amount
the idea is to display the frame twice or three times for
In other words, the monitor would be reproducing the 24p fps
48 or 72 times a second. Each CRT monitor then would require a
that would be filled in 1/24 second but read out then
or three times during that 1/24 of a second. The price of the
probably be a little more expensive initially because of
frame buffer. To make the monitor work at other standards
more costly and would still only show the same image, no matter
rate, interlaced or progressive.
the DTV standard the display is handled in the receiver, it is
in the home. In the production and post production areas, a
need to view
the images before they are compressed and transmitted is
Engineering and creative judgments have to be made to evaluate
A few years
ago people who use surveillance cameras to record images of
and holdups asked for a way of improving the clarity of
on playback. A few cameras, developed by Sony and
the images with a 30p fps camera that output the image
as a 60sF
image. In those countries that are at 25 fps, the camera
from the 25p fps images. These images were easily recorded
equipment and worked quite well. As a matter of note,
images scanned today, on most Telecines, are scanned
The resulting image is read out as two fields. Those two
reality are two segmented frames, frame one containing all
even lines and frame two containing all odd lines.
3:2 is added for the
to 30 fps as there has been no requirement for 24 fps. In 25
the image is scanned progressively and read out as two
frames also. There is no need for a 3:2 conversion.
So the decisions
that have to be made are: Do we come up with another
48sF, or do we stay at 24p (25p) only and convert at
device (if it is a CRT) using 48 Hz (or 50 Hz) with flicker,
or a flicker-less
display at 72 Hz (or 75 Hz) repetition rate.
devices like the flat panel plasma display, Texas
DMD (Digital Micro mirror Device), or the LCD and D-ILA
Light Amplifier) do not require any conversion from the
as their images are updated almost instantly. There is no
the image with time. The image is there until each pixel is
unlike the decaying phosphor image.
discussed was the need for a standard format conversion
or 48sF to those frame rates that are not simple multiples of
the 24 or 25 frame rate. An example is 24 fps
to 30 fps. In Hollywood,
3:2 can be
a nightmare if the sequence is interrupted. Today there are
out in the market place that do not have a continuous 3:2
Some have intermittent 3:2, 2:3, 3:2, etc. sequences, due to
video editing. True, one can be meticulous in keeping an eye on
the 3:2 sequence,
but "Murphy's Law" says it will happen and it does. To
for MPEG encoding, be it SDTV or HDTV, when the sequence is
out of order,
will cause some artifacts.
I believe that 24p at 1080x1920 should be the mastering
and any conversion for processing and/or display be
in those devices. Otherwise there will be a
of intelligent sequencers and de-seguencers needed to keep
in order. 24p is the K.I.S.S. (keep it simple stupid)
without playing the numbers game and giving the production and
industries a standard that will work. Adding another
to the 18 ATSC standard is not wanted or desired.
Not too long
ago I was giving a presentation to a network affiliate in one of
the top 10
markets on a system of managing multichannel television program
material. They, like many other broadcasters,
are faced with the option of
to attract more advertising revenue by simultaneously offering more
widely diverse programming using multiple channels.
The reasoning is that,
there is a finite and limited number of advertising dollars in any
if we can offer viewers most everything they want, they'll not
have to go
else were, and the same applies to the advertisers and their
dollars." Although I don't think that
they really believe they'll get all the
dollars, it is reasonable to think that if you do offer more of
want, you'll get a greater percentage of that available revenue
at the presentation seemed to be impressed with the ability and
which they will be able to manage the various aspects of
television, but their main concern, and one that seems to be all
and growing exponentially with the approach of the "turn on
is how they will do local origination, giving their viewers good
sound, etc. and not try to make a silk purse out of a sows
ear by bumping
up from NTSC.
I've not mentioned who these folks are is because they've asked
not too. I find engineers are more open
if they can trust you when sharing
offered by the engineers at this meeting to the lack of available
video for digital TV is to bring back the telecine chains.
Remember: academy leaders, hairs in the gate,
the broken splices, etc.? I
they were serious and if the lack of HDTV programming on tape was
scarce and the response was, without hesitation, was-yes!
a few years back trying to raise the money to build a telecine
facility for the purpose of doing film to "data"
transfers. I knew that it
a matter of time when there would be a big demand for program
material in formats other than NTSC or PAL.
I still believe that if movies
digitally put on tape, capturing the highest number of component
possible, that they could be reassembled, during playback,
in almost any format the user might need, including
HDTV. I knew that this
done, to a limited extent, with digital videodisk (DVD), but they
were only opting for quality slightly greater
than NTSC. I have never figured
out why they didn't master with HDTV in mind.
You can always get rid of bits
need, but the picture will look like *=&% if you try to insert
there that was there to begin with.
Another, less acceptable, solution for quality
video for DTV is the DVD. I
know of several
stations that are using DVD today, with its NTSC output for
various repetitive playback situations, such
as promos, Ids etc. There's no
you can get the required clearances, why you couldn't play movies
to air from DVD. There are no tape dropouts
(unless you recorded them there),
to get a crease in a DVD and I've never heard of one being erased
not an immediate answer to the lack of quality video one other means
distribution was mentioned; getting program material delivered
directly on a server. Now wait a minute.
Don't laugh. Think this out. Why
an HDTV movie, at a very slow bit rate, at any time of the day,
directly into a server, via low cost telephone
lines. It may take 4 or 5
long to get the movie onto the hard drive as it does to play it
but who cares. All it takes is about 12
Gbts. total storage capacity for a
2-hour movie. This approach does have some
merit and it is a step toward a
Two on One
I don't know
how it is where you're at, but one of the loudest screams you can
hear in our
industry today, followed by, "You want to do what?" comes
local frequency coordinator when you ask for
a new microwave path.
of the 2 GHz channels going away and the fact that those remaining
DTV, many stations are having to look at other equipment,
ranges and even the possibility of abandoning their STL in favor
replacing it with fiber to get their signals
to the transmitter site. I did a
too long ago about a company who had developed a technique of
the analog NTSC signal to digital and feeding it and the ATSC
digital signal on the same digital STL link.
I wondered, at that time, if
come up with a way to combine the two services on the same path.
Radio Communications (MRC) has come up with their TwinStream radio
they say is the first dual carrier radio system for the
of uncompressed legacy NTSC plus ATSC signals in a single 25 MHz
MRC has applied for a patent for what they call the "Gemini
to combining analog and digital signals as offset "intermediate
frequencies" (IF) in microwave system design.
It sounds like this is one
solution for the studio-to-transmitter link (STLs), transmitter-to-
(TSLs), and satellite backhaul requirement issues.
stream system permits DTV studios and transmitters to coexist with
the legacy analog infrastructure. Since
the FCC has not given any additional
up to accommodate the new DTV requirements, finding an STL
solution has been a challenge. The twin
stream approach will eliminate the
cost of digitizing and compressing NTSC programming to transport
across an STL in concert with the DTV signal.
One other issue is that this
avoids the latency problems that are inherent to all current video
information see MRC's web page at http://www.calmike.com
Similar but different - Two Inputs, One Output
a Chief Engineer or General Manager a live that isn't looking for
a way to
find the extra money to make the transition to digital television
then the bucks to keep it running. Any
savings in equipment or operating
costs should be an answer to a prayer.
If you are one of the 320 stations who
assigned your DTV channel next to your NTSC channel, there may be
cost savings answer from Acrodyne.
of putting ten pounds in a five-pound bag has captured the
imagination of many. Well, may be it isn't
quite as impossible as it may
seem. We've been transmitting two different
signals, on two different
all going out into the same antenna (in most cases) since the
of television; vestigial sideband (visual/picture) and frequency
modulation (aural/sound) and right next to each
other frequency wise. Until
1980's the combining of these two signals/transmitters was done
their outputs and at relatively high power levels.
Dr. Tim Hulick, Vice
of Engineering at Acrodyne told me in a telephone interview, that
Acrodyne, pioneered low level combining and subsequent
of two different RF signals.
to reason, with Acrodyne's experience in combining different types
of low level,
RF signals; they would probably be looking into the NTSC/DTV
issue. Why not combine the output of an
NTSC exciter through a hybrid with
the output of an adjacent channel DTV exciter?
If that were possible and your
antenna was broadbanded enough, it should work.
Well, Dr. Hulick told me,
it's not quite that simple.
you who have kept up with all this DTV stuff know that the DTV
has to be ultra linear and there is a lot of electronic correction
shaking" going on between the amplifiers and the exciter to
make it all
. Considering the adjacent channel situation,
there are two scenarios: one,
DTV channel is below (n-1) the NTSC and two, where the DTV channel
is above (n+1). In the first instance (n-1),
albeit sufficient guard band is
design and build a channel combining filter system enabling the
user to pipe both signals to a common antenna.
In the (n+1) case, the
solution isn't so simple. There is virtually
no guard band between the
making the filter combiner solution impractical.
to Dr. Hulick, the real answer to both situations (n-1 & n+1)
lie in using
a common high power amplifier for the NTSC and DTV signals. If
be successfully done, a combiner wouldn't be needed, but it
a very linear amplifier; one that is capable of meaningful peak
tubes of choice today, for high power at UHF frequencies are the
klystrode/IOT and Diacrode, the best of the types had to selected
only for power bandwidth, but also linearity.
The TH-680 Diacrode cavity
tuned for a one dB bandwidth of 14.6 MHz puts
it in the ballpark. Tuned this
flat, put it sufficiently far enough away from the channel edges
that group delay would not be a problem.
The Diacrode is the highest power
UHF amplifying device suitable for TV broadcasting.
It is capable of at least
104 kW of
unsaturated peak envelope power giving it a rating of 60 kW peak
sync along with simultaneous provision of 6 kW
of aural power.
certainly has made a strong argument for this type of transmitter
under these circumstances. They've developed
a transmitter that will do all
this, both N-1 and n+1. They call it their
Adjacent Channel Technology or
ACT, for short, transmitter.
John Long, VP of Engineering at the PBS station in the nation's
market, Kansas City, MO, KCPT-TV believes it will do the job for
him. Acrodyne will install the transmitter
at KCPT-TV, to be on the air by
November 1, 1998. KCPT presently broadcasts
on channel 19 and has been
assigned channel 18 for KCPT-DT. The Diacrode
equipped UHF ACT transmitter
will deliver 60 kW NTSC and 3 kW DTV to meet
FCC ERP requirements. They're
doing all this in just 4 equipment cabinets.
Long is a pretty busy man these days with that
kind of a deadline. In a
telephone interview, he told me that he feels comfortable with,
is committed to taking advantage of, the new
technology: "We look forward to
switch-on November, 1st." Nothing
was said about local origination or network
feeds. Does leave one to wonder.
The DTV Tech Notes are published
for broadcast professionals who are
in DTV, HDTV, etc., by Larry Bloomfield and Jim Mendrala. We can
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,
opinions, etc., are always welcome from our readers; letters may
brevity, but usually not.
--------- J_Mendrala@compuserve.com <<<
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