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HIGH DEFINITION VIDEO RECORDING FORMATS
As your present analog and digital video recorders grind themselves
into retirement, you may be wondering what format the next round
of VCRs need to be. Perhaps your postproduction facility, school,
or business is gearing up for the coming of HD (High Definition)
or perhaps you are a broadcaster feeling the hot breath of the
FCC with its impending requirements to broadcast in DTV. Of course
you could stick with the present standard definition (SD) gear
and using an upconverter, change whatever you are using now to
"pseudo HD", something with the data structure of HD
but lacking the true high definition. Or, maybe you will go all
the way, forging a path onto the nascent landscape of high definition
television recording.
Whatever you do,
the coming HD revolution is likely to make pioneers of many of
us. It will be easy to tell which of us were the pioneers; we'll
be the ones with the arrows in our backs. That's because the decision
to move into HD will be expensive and dangerous. The list of what's
available and how much it costs will change rapidly making almost
any decision you make a short term one. Put another way, whatever
you buy, needs to be supported by a business plan that shows heavy
use of your HD purchase so that it can be amortized over two or
three years. Let me put it still another way, because this is
important. Your HD recorder will cost between $40,000 and $100,000,
based on what's available today. As new products reach the market,
competition will drive some of these prices down. If a gizmo you
paid $80,000 for today can be replaced by another gizmo that costs
only $40,000 two years from now, you'd better have a plan to work
the heck out of that $80,000 gizmo if you want to compete two
years from now with your neighbor who will then be buying a $40,000
gizmo that's better than yours.
Although
this is an article about formats, it's not very instructive to
compare technical specifications like track length and data rates.
These riveting tidbits are available through SMPTE at smpte.org.
It's the implementation of the format that counts, so let's see
what the VCR manufacturers are doing.
Some generalities about HD recorders
You have three kinds of recorders out there;
the expensive, no-holds-barred, high bit rate recorders that suck
up data with wild abandon, you have the the newer HD recorders,
and you have the common SV recorders like DVCAM, DVCPRO50, D-9,
D-7, etc.
The top-of-the-line recorders (i.e. D6, HDD1000) can handle HD
but are too expensive to be practical.
The SD recorders don't have a chance of recording all that data
unless you compress the beegeebers out it. It can be done, though.
Just slap an encoding processor onto an SD machine and squash
away. Although this sounds like a bad solution, it's not so bad
if the SD machine started with a high bit rate. Panasonic's D-5
recorder, for instance, records 235 Mbps uncompressed SD CCIR-601
data. It's not a huge leap to add a processor to the existing
D-5 machine and squash the raw 1.5 Gbps HD data down to 235 Mbps,
making an uncompressed SD recorder into a compressed HD recorder.
Other popular solutions: speed up the SD machines (usually doubling
the tape speed, head rotation speed, and bit rate) and also compress
the data mildly. The combination balances between the expense
of high bit rates and the sharpness-damaging artifacts of compression.
Who has what?
JVC offers D9-HD based on its D9 (also called Digital S) format
VCR.
Second in JVC's HD arsenal is W-VHS, an analog component video
recorder/player used primarily for playing HDTV recordings.
Another format, D-VHS, is designed primarily for recording and
playing back pre-encoded MPEG-2 data streams like you might get
from a satellite receiver. JVC and Panasonic sell it.
Sony offers two HD video production formats, the HDD1000 1"
reel-to-reel studio recorder that handles uncompressed high bit
rate data, and its more affordable and more popular HDCAM.
Panasonic offers three formats, the high end D5-HD, a high bit
rate studio deck modeled after the D5 format, and its more moderately
positioned DVCPRO-HD, modeled after its DVCPRO (also called D7)
line. Panasonic also offers a D-VHS deck.
Let's take a look at these formats one by one.
JVC's D9-HD
The D9-HD format offered by JVC is modeled after its D9 (Digital
S) recording system. They are switchable between 720/p60 (720
scanning lines per picture, progressively scanned, 60 times per
second and 1080i60 (1080 scanning lines per frame, interlaced
with 540 lines per field every sixtieth of a second), as well
as 1080p24 (1080 scanning lines per frame, progressively scanned
at 24 frames per second with each frame containing 2 fields with
540 lines each). According to Dave Walton, D9-HD is "designed
to be a cost-effective high quality digital recording format that
offers practicality that one would get with an SD format. For
example, with a D9-HD we have a recording time on camcorders as
well as studio decks of 62 minutes.
"The logical comparison with any six
millimeter format is going to be regarding the amount of data
you could put on a tape. We use ½" metal particle
tape and ½" tape gives you the ability to record essentially
more data and have longer record times. It also provides backwards
compatibility with D9."
The D9 HD compression scheme is DCT (Discrete Cosine Transform)
and uses a mild 3.3:1 intraframe compression. Although some manufacturers
list a luminance and chrominance bandwidth for their HD VCRs,
JVC does not. As Dave Walton explains, "The D5 machine has
no analog inputs or outputs on it. Therefore, you can only feed
a digital signal into it which doesn't have a bandwidth associated
with it. If you are looking at the encoder or decoder that's used,
then you are not measuring the frequency response of the video
deck but the frequency response of the encoder. If you use the
same encoder with a D5 machine as you used with the D9 machine
or HDCAM, you'd have exactly the same spec, if in fact the sampling
frequency of the video and audio were the same. The only difference
would be in the compression algorithm. In D5, for example, it's
a DCT based compression of about 4 ½ to 1. An HDCAM has
a compression ratio of 7 to 1. But they are both recording the
same sampling frequency of 74.25 MHz (MHz). So the difference
is not in frequency response, the difference is in how much degradation
takes place in the compression algorithms. The sampling frequency
is fixed, thus the inherent resolution is fixed."
JVC's ½" metal particle video cassettes are modeled
after a VHS cassette shell and cost about $45 for a 62 minute
DS-104 cassette. JVC points out that 62 minutes is a long recording
time for a standard sized cassette. The small camcorder cassettes
used by HDCAM and DVCPRO-HD run 40 and 46 minutes in length respectively.
The other formats require a large cassette, inappropriate for
camcorders (to get recording times up to 124 minutes).
The D9 format can record up to 8 editable 16 bit audio channels.
[See Compression vs. Picture Sharpness for related information]
JVC's D-VHS
D-VHS is the digital version of VHS capable of recording MPEG-2
data like the kind transmitted via a satellite and will be transmitted
by DTV broadcasters. As explained by Dave Walton," The D-VHS
format is able to record 28.4 megabits per second on a standard
oxide VHS-like cassette that sells for about $8. This adds up
to about 45 Gb (gigabytes) or nine times the capacity of a DVD
that can be recorded on a D-VHS cassette. Put another way, you
can record a 3 ½ hour HDTV movie with the full HDTV quality
on one cassette. The D-VHS machines would provide forward and
backward compatibility with VHS machines already in use. There
are a billion people now who have VHS machines and libraries of
this material that they will be able to view 10, 15, or 20 years
from now."
The D-VHS format is a marriage of two things: tape speed (which
is proportional to the amount of data that is recordable and inversely
proportional to the length of recording that can fit onto a tape)
and the amount of MPEG-2 compression used. For instance, a high
definition MPEG-2 data stream with reduced compression would require
the machine to run at its fastest speed, recording maybe two hours
at 28.4 megabits per second. A more compressed HDTV signal transmitted
using the FCC mandated bandwidth of 19.4 megabits per second would
permit the D-VHS VCR to record at a slower speed, recording 3.5
hours of an HDTV signal (but with more artifacts and less quality
because of the increased compression). MPEG-2 can be adjusted
to very high compression rates permitting as much as 49 hours
to be recorded on a D-VHS tape. Thus the D-VHS format is extremely
flexible allowing a wide range of image qualities and record times.
The D-VHS machines cost about $1000 and a 300 minute DF-300 cassette
costs about $8 making D-VHS a very affordable way to store HDTV
once it has been encoded. Although previous models required external
encoder/decoders, JVC is now introducing models with built-in
encoder/decoders with IEEE 1394 inputs/outputs.
D-VHS machines are not production recorders as the data has been
far too compressed (using interframe compression) to be editable.
"I'm not sure what all the applications for that might be,"
says Dave Walton, "but it is reasonable to believe that there
will be some applications in the production process for D-VHS
machines whether it be archiving material off your hard disk or
long recording times for DTV material. D-VHS is a long term format
for both standard and high definition recording. The original
designation of this format as simply nothing more than a 'bit
bucket' has somewhat changed since the announcement in Japan of
the D-VHS machines with built-in MPEG-2 coders and decoders. The
bottom line is that a D-VHS machine is a VHS-type machine at extremely
low cost that is specifically designed to record formatted MPEG-2
data whether that MPEG-2 data is created in the machine or supplied
externally. But MPEG-2 has been decided upon as the transmitted
DTV format so this recorder is designed to record and play that
back at minimal cost and maximal benefits for the user.
"Our consumer division has been selling D-VHS format machines built into a dish network receiver for several years now. In the past couple of years, the only source of digital programming to the user at home has been through the satellite receiver. So, the only digital recorder practical for the home has been the D-VHS machines built into the satellite receivers that let you record and playback the signal you were receiving from the satellite."
JVC's W-VHS format
-
Unlike the other formats, W-VHS is analog, recording and playing
the standard Y/Pb/Pr video component signals used by HD VCRs,
monitors, and set top boxes. JVC is presently marketing the $4795
SR-W5 model and the $5950 SR-W7 model, the latter having BNC connectors
and time code. W-VHS can record high definition 1035i, 1080i,
or 1125i component analog signals. W-VHS machines can record or
play regular VHS tapes, but when used with the high grade WT-120
($65) or WT-180 ($80) metal particle VHS-like cassettes, the W-VHS
machines can record and play the higher definition signals. Although
they are not meant to be editors, the W-VHS models have assemble
edit and audio dub capabilities and a VGA output for use with
computer monitors.
According to Dave Walton, W-VHS "is an outstanding distribution
format. We have corporations that pay megabucks to have large
screen productions made for corporate meetings. Advertising agencies
want to be able to view commercials. Even people in the home theatre
environment may want to record a high definition football game
in the home. What are their options? The fact is it'll plug into
any DTV desktop box and record your game, it will plug into any
HD camcorder, it will plug into any D5-HD machine. Y/Pb/Pr is
the component standard, whether it's on a monitor or on a set
top box.
" Another benefit of the W-VHS recorder is that we have provided
a VGA output on the back so it can be plugged into a computer
monitor so it can be used as an inexpensive HDTV monitor. "
Although W-VHS and D-VHS are both at the low end of the HD format
spectrum, the two have about as much in common as lightning and
lightning bugs. Both are backward compatible with existing VHS
recordings but W-VHS is strictly an analog record/play mechanism
while D-VHS is strictly digital. If you are starting with analog
component video, you can feed it directly into a W-VHS machine.
The D-VHS machine needs the video to be digitized and encoded
(compressed) into an MPEG-2 datastream (internally or externally)
to be recorded.
Panasonic DVCPRO-HD
DVCPRO-HD is a production format on a par
with JVC's D9 and Sony's HDCAM. It is built on (and backward compatible
to) the DVCPRO format (which is also called D-7).
Panasonic will be offering two camcorders shortly after the first
of the year, the AJ-HDC10 ($50,000) and the AJ-HDC20 ($65,000),
the first having one million pixels per CCD and the second having
2.2 million pixels per CCD. (Camcorder prices are always quoted
as list and without lens.) There is also a studio recorder, the
AJ-HD150 ($65,000).
Although the camcorders operate in the 1080i (also 1035i ) domain,
the studio recorder is a little different. According to Jeff Merritt,
Panasonic's Product Marketing Manager for HDTV, "The HD150
is a native 1080i recorder but with an optional built-in universal
format converter. The HD150 is playback compatible with all DV
formats --- that's all DV --- That's mini DV, that's DVCAM , that's
DVCPRO, 25, 50 megabit, progressive, any DV format. When using
a format converter, it is possible to play back any of those DV
formats, or DVCPRO formats and output either 1080i or 720p. "Not
only is the HD150 studio deck compatible with all of the other
DVCPRO and DV products on the market, it has eight channel digital
audio capability and it's compatible with metadata and ancillary
data recording. That's already built-in, it's not optional; that's
part of the format. Metadata is data about data. Ancillary data
is such things as closed captioning, it could be setup functions,
it could be all kinds of other things, but they are pretty well
clearly defined as not being data about data but being data by
themselves. That is what is called ancillary data. SMPTE is working
very diligently on making all of the standards of this stuff work."
Jeff Merritt goes on to say that the DVCPRO-HD format "...
is is an extension of the entire strategy of Panasonic of not
abandoning any previous formats but moving forward into newer
technology with existing formats. In other words, DVCPRO25 was
the first of the really large scale DVCPRO products to go virtually
worldwide. And Panasonic developed the next version of that to
deal with not only 25 megabit but 50 megabit 4:2:2 for example
rather than 4:1:1. It is still backwards compatible with 50 megabit
equipment, and backwards compatible with 25 megabit equipment.
Now we get into 100 megabit equipment. It's still compatible with
the 25 and 50 megabit stuff for playback. So we're staying with
what works, with what has been accepted worldwide as a standard.
"The DVCPRO-HD
VCRs are compatible with other manufacturers' DV products; you
can even play back a DV tape made on a home DV camcorder. The
advantage is for people who have already acquired a library in
either the 25 megabit or 50 megabit DVCPRO material. That material
is not obsolete, that material can now be repurposed by being
up converted to the 1080i or 720p and mixed with other high definition
material. "
DVCPRO-HD uses DCT compression like the other DV formats, but
it is variable up to 7:1, depending on what's in the image.
The camcorders operate at 59.94 fps (fields-per-second) only,
the studio model is switchable between 59.94 and 60 fps.
The format supports eight discrete 16 bit audio channels at 48
Khz sampling. The Panasonic camcorders are unable to edit these
audio channels but the studio deck can.
Although the ATSC table lists 1080 x 1920 pixels for an HD picture,
the DVCPRO-HD studio machine is only capable of recording 720
x 1280. You can feed it 1080 x 1920, but it records and plays
back only 720 x 1280, with some pixels obviously manufactured
by the machine. This "cheat" was necessary to reduce
the data rate to the 100 megabits per second range manageable
by the VCR.
Panasonic doesn't presently support the 1080p24 format with DVCPRO.
According to Jeff Merritt, "it's under development".
One welcome surprise is that the DVCPROHD machines from Panasonic
all use standard DVCPRO tape, so you don't have to stock another
tape flavor on the shelf.
Panasonic D5-HD -
D5-HD is Panasonic's top of the line high definition format. D5-HD
is a studio production format. The VCRs are studio consoles only,
there are no camcorders. Although it is based on its standard
D5 format, the HD machines will not play D5 standard definition
tapes.
Jeff Merritt explains the background of D5-HD: "We have to
take a look at the history of D5 and work up to D5-HD to understand
what's going on here. D5, a SMPTE format, is uncompressed, what
we call CCIR601. It is an integral serial digital component 4:2:2.
Well, what we did was to take that basic format and married an
AJ-HDP500 high definition processor with the D5 format and then
were able to put up to 235 megabits on tape working in the high
definition domain at 1080i." In other words, the DCT processor
compresses the 1.5Gbps found in the CCIR601 uncompressed data
stream down to the 235Mbps recordable on tape. "Now from
there we incorporated the HDP500 processor into the next generation
of the machine which became the AJHD2000 which has since been
discontinued, replaced by the HD2700. Where this gets us is to:
a strictly HD only machine, the AJHD2700 that's compatible with
native 720p and1080i, full bandwidth 4:2:2. The original AJ-D580
machine still exists and we still sell many of them. As facilities
are moving from analog to digital, they would like to go uncompressed
and they can do that with the D5. We have announced a new tape
machine whose model number is currently AJHD3000 that incorporates
all D5 formats in one machine including D5, uncompressed CCIR601,
1080p24, 1080i 720p, all in one machine. It records and plays
all D5 formats and an optional universal format converter can
be part of the package."
Panasonic's first deliveries were in the summer of 2000. The AJ-2700
costs $99,000 as will its successor the AJ-HD3000. The AJD580
(standard definition D5) costs $72,000 and the AJ-HDP-500 processor
costs $52,000. The combination of these two devices will make
high definition video.
Panasonic's D5 HD machines, because they are based on the D5 format,
work in the full bandwidth 10 bit domain (there's no prefiltering
or postfiltering of the signal as is done with the Sony HDCAM.
Also the HDCAM works only in the 8 bit mode.) Panasonic's D5-HD
is also switchable to an 8 bit mode. While in that mode it uses
a 4:1 intraframe compression. In its 10 bit mode, it uses a 5:1
intraframe compression.
The VCR is switchable between 59.94 fps and 60 fps.
As with the DVCPROHD studio deck, the new D5-HD VCR has 8 editable
audio channels.
One thing setting the D5-HD apart from other formats is that it
records a true 1920 pixels by 1080i image (Panasonic's DVCPROHD
records only 1280 pixels and Sony's HDCAM records only 1440 pixels).
It is also switchable to 1035i and 720p. One reason why the D5-HD
machines can record such a detailed picture is that they're throwing
235 megabits per second onto the tape, (as opposed to DVCPRO-HD's
100 megabits per second, D9-HD's 100 megabits per second, and
HDCAM's 140 megabits per second).
Who's using this format? Jeff Merritt explains, "It is the
defacto standard of high resolution recording and playback for
high definition. Every motion picture company, every high end
posthouse in the Hollywood community and the New York community
is working in high definition, virtually every broadcast network
is recording or originating in HD. It is the delivery standard
of choice for all of these people, the networks in particular
including HBO. When you watch ABC Monday Night Football in high
definition, you see instant replays done on D5-HD, on the HD2700,
for example. This was the format chosen by the Lucas organization,
Lucas Arts, to master the Star Wars Trilogy on."
Panasonic D-VHS -
Although DVHS, as mentioned earlier, is not a production format,
it is still a high definition video recording format. Panasonic's
PV-HD1000 costs under $1000 and is now available. It connects
to a set top box which decodes satellite TV signals and feeds
them to the VCR via an IEEE 1394 connector. The PV-HD1000 is essentially
a "bit bucket" recording and playing raw data and doing
nothing with it. When the data is played back, the signal is fed
out through the IEEE 1394 connector back into the decoder which
feeds the television via the set-top box. Unlike the JVC model,
the PV-HD1000 has no MPEG encoders or decoders. Like the JVC model,
it will record and play standard VHS and SVHS tapes. When recording
MPEG-2 data, however, one must use D-VHS tape, a higher grade
½" metal particle tape similar to that used for SVHS.
The PV-HD1000, according to Jeff Merritt, is popular among broadcasters
playing back videos in their lobbies.
Sony HDCAM-
HDCAM uses a Betacam-like cassette with metal particle tape but
none of the present VCRs are backward compatible with Betacam,
DVCAM, or other formats (this may come later). Presently available
is the HDW-500 studio deck ($61,400), the HDWF-500 studio VCR
($69,300), the HDW250 portable deck (no price available), and
HDW-700 one-piece camcorder ($78,800). All work in the 1080i native
domain, but with an additional circuit board, the output can be
converted to 720p. The HDWF-500 can record and play in 1080i and
1080p24.
There are four models of tape to feed the hungry HDCAM. Only the
studio VCRs can take the BCT-124HDL (124 minute) and BCT-64HDL
(64 minute) large cassettes. The camcorders and studio decks both
accept the BCT-40HD and BCT-22HD mini cassettes (which run 40
and 22 minutes respectively).
The main advantages of selecting HDCAM over other formats, according
to Robert Ott, Vice-President of VTR/Storage Marketing and Products
is "that we've had an acquisition piece as well as a full
studio VTR available for more than a year now. We have them in
active use on major television shows such as Chicago Hope. It
was the equipment that was used to produce the first high definition
regularly scheduled program which was the Tonight Show. We've
go a track record. Without a doubt, the HDCAM format, because
it has had acquisition from day one, has made it a very viable
format because it is not just an editing format such as telecine
transfer or studio camera oriented; it's truly electronic field
production and electronic cinematography. So, people are out there
shooting in HDCAM right on their shoulder and that's a big advantage
of this format. It is robust, it holds up just like the Betacam
format which has a very good reputation. HDCAM has that same reputation
for taking a beating and keeping on taping."
Sony is tight lipped about publishing details such as compression
ratio, sampling frequencies, bandwidth, and the like. Sony will
tell you that it uses DCT intraframe compression, but it's up
to the user to do the math and conclude that it uses 7:1 compression.
Says Robert Ott, "We've been making ½" transports
since 1982 in the form of Betacam, so basically, if we forget
all the compression issues and everything that has to do with
picture quality, if we just talk about someone taking a camcorder
out and beating the heck out of it, for lack of a better term,
we know we have products that take that kind of punishment and
that's what the industry is looking for because they do beat the
heck out of it. Not intentionally, but you know, they are on a
rollercoaster, they are climbing mountains, they're doing everything
with this equipment and they need a tape format that is a proven,
reliable tape format. HDCAM, because it is based on ½"
tape and we have so much experience in building transports, will
take G-forces and everything else. HDCAM just lives off that legacy
of ½". Basically, our philosophy is you can take a
tape that was recorded in 1982 in a Betacam deck and play it back
in a digital Betacam deck that was purchased last week. And that's
the philosophy that we intend to follow through on all of our
products."
The ATSC (Advanced Television Systems Committee) tables indicate
that a 4:2:2 sampled 1080i image should have 1920 luminance pixels
in the image. Chroma should be 960 pixels. Put another way, the
4:2:2 sampling should translate to 1920:960:960. Sony's HDCAM
is said to record only 1440:480:480 pixels. If you do the math,
this translates to 3:1:1, a number worse than 4:2:2. The numbers
don't tell you everything, however; the HDCAM image is gorgeous
and Sony challenges anyone to see the difference between the HDCAM
output and that of its rivals.
The 3:1:1 numbers would
also imply that the image is worse than a consumer DV camera (4:1:1)
and this definitely not the case. A home DV camcorder has a sampling
of 13.5 MHz yielding 720 pixels per line. According to the ATSC,
HD is sampled at 74.25 MHz (true whether the format is 1080i,
1035i, or 720p) yielding 1920 pixels for luminance per line. Thus,
4:1:1 in the SD DV world means 720:180:180 pixels. In the HD world,
4:1:1 would mean 1920:480:480 pixels. So you can't compare DV's
4:1:1 with HDCAM's purported 3:1:1; that would be comparing grapes
to grapefruit.
Now here's the
real concern: HDCAM supposedly uses a 55.68 MHz sampling rate
which should technically resolve to 1440 luminance and 480 chrominance
pixels per channel. Comparing these numbers to the ATSC HD specs,
we would come up with the number 3:1:1 which looks below par.
When pressed on the issue of how many pixels are being recorded
by the HDCAM machines, Robert Ott could only state; "The
HD SDI signal from an HD SDI standpoint, based on the SMPTE 292M
standard, facilitates a 1920 x 1080 pixel baseband digital capability."
The author conjectures that the VCR manufactures the missing pixels.
Whether they're visually missed is a tough question. You remember
(no doubt) from the sidebar earlier that if you have more data
but compress it more, you hammer the picture sharpness.. Less
initial data, compressed less, could look just as good.
The HDCAM
is an eight bit machine, but Robert Ott goes on the explain, "HDCAM
uses eight bit data reduction, but from a quantization standpoint,
the inputs and outputs are ten bits. So, from a compression standpoint,
we're eight bit data reduction. But from a quantization standpoint
in the video, we're ten bits on the inputs and the outputs. "
Although Sony doesn't publish the number of bits being recorded
on the tape (it's purported to be around 140 Mbs per second),
Sony has interface boards that output whatever bit rates that
are needed, such as 1.5 Gbps and 270Mbps SDTI.
Robert Ott was careful to point out that any rumors of Sony replacing
its DCT compression with an MPEG-2 compression in the near future
is totally false. Sony plans to support DCT compression in their
HD line for the foreseeable future.
The author would not be surprised to see MPEG-2 rear its head
in some HD product down the line. If you consider the Sony Betacam
SX is MPEG-2 based at the standard definition 480i, it wouldn't
be an outrageous leap to double the tape speed, add a little more
compression, and go HD. The author would further conjecture that,
at some time in the future, Sony would make a deck that played
all their legacy formats besides (SX, digital Betacam, and HDCAM),
since they all use the same sized tape.
Back to known facts, all HDCAM models will operate in both the
59.94 and 60 field per second modes.
HDCAMs have four editable 20 bit, uncompressed audio channels
capable of 20 KHz frequency response. According to Robert Ott,
"The 24p as well as the 1080i machine will be Dolby-E compatible
which means that you will get eight channels. Two [of the format's
4] channels remain compressed, and the other two channels (When
you record in Dolby-E, you are taking up two audio channels),
can be converted to eight using Dolby-E. And the nice part about
using Dolby-E is that all eight channels are still editable,"
unlike Dolby AC3 where once the signal is encoded it is no longer
editable.
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