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LaserDisc (LD)
DVD's immediate predecessor, the LaserDisc system stores high quality
audio and video on a 12" (or 5") optical disc. Physically similar to an oversized CD,
virtually every LaserDisc player manufacturered since 1986 will also play conventional
CDs. One 12" LaserDisc is capable of storing approximately sixty minutes of
video material on each side of a CLV (Constant Linear Velocity) disc, or 30 minutes
on each side of a CAV (Constant Angular Velocity) disc. Because of these playback limitations,
movies over two hours in length are usually recorded on two or more discs. Many players
include an automatic side change function, which allows up to two hours of continuous
viewing (albeit with a slight pause of up to fifteen seconds as the side is changed). Both
Dolby Digital and DTS were first used on LaserDisc.
Dolby Digital LaserDiscs
require a LaserDisc player with an 'AC-3 RF Digital Out', while DTS discs may be played
on any LaserDisc player with an S/PDIF digital output (TosLink or coaxial).
DVD
The same size as a CD, a DVD is capable of storing significantly
more data (18 gigabytes compared to 680 megabytes on a CD). DVD's features
include: Dolby Digital, PCM, MPEG or DTS soundtracks, multiple aspect ratios (fullscreen
and/or letterbox depending on the DVD), up to 8 language tracks, up to 32 subtitle languages,
alternate camera angles, and parental lockout functions. Many discs also contain extra
features
such as production material and director's commentary. DVD is capable of approximately
500 lines of horizontal resolution, compared to VHS's 240, Super VHS's 400 and
LaserDisc's 425.
For more be sure to read Jim Taylor's
excellent DVD FAQ Page.
Dolby Pro Logic
Developed in the mid-1980s by Dolby Laboratories, Dolby Pro Logic is essentially
the domestic version of Dolby's theatrical 'Dolby Stereo' system. Currently
the defacto standard for home theater, Pro Logic extracts four
channels of information (left, center, right and surround) from 'Dolby Surround' encoded two
channel material on DVD, LaserDisc, VHS, CD, MTS etc. Dolby Surround soundtracks
include full-range left, center and right
channels, and a limited range mono surround channel (100Hz to 7kHz). Not all channels
can contain all
frequencies at the same time, and channels must interact with one another to varying
degrees. To overcome these limitations, fully discrete systems such as Dolby Digital
and DTS Digital Surround were developed.
Dolby Digital (DD)
Formerly known as 'AC-3' or 'Dolby Digital AC-3', Dolby Digital is a versatile,
high-quality audio compression system. Dolby Digital allows five discrete full-range
(20Hz to 20kHz)
channels (left, center, right, left surround, right surround), and a limited frequency
(20Hz to 120Hz) LFE or Low Frequency Effects channel to
fit into one quarter of the space previously needed to reproduce CD's two channels.
Dolby Digital's first theatrical appearance was in the 1992 release Batman Returns;
its first domestic appearance was on the 1995 LaserDisc release of Clear And
Present Danger. Dolby Digital is one of DVD-Video's audio standards, and is used on
virtually all DVDs.
DTS Digital Surround (DTS)
Digital Theater Systems describe their DTS Digital Surround system as follows:
An amazing new technology for surround-sound entertainment, DTS Digital Surround is an
encode/decode system that delivers six channels (5.1) of master-quality, 20-bit audio. In
the encoding process, the DTS algorithm encrypts 6 channels of 20-bit digital audio
information in the space previously allotted for only 2 channels of 16-bit linear PCM.
Then during playback, the DTS decoder reconstructs the original 6 channels of 20-bit
digital audio. Each of these 6 channels is audibly superior to the 16-bit linear PCM
audio found on conventional compact discs.
THX (Tomlinson Holman's Experiment)
LucasFilm describe the THX mastering and certification program as follows:
The THX Sound System was developed in 1982 during the production of Return of the
Jedi. Inspired by George Lucas' interest in upgrading film presentation standards in the
industry, Lucasfilm's Corporate Technical Director, Tomlinson Holman, began to identify
problems related to theatre sound. Holman noted theatre audiences were not hearing what
was recorded in the film studio - many of the subtle sounds were missing. His innovative
approach was to consolidate existing performance standards into a new system which included
theatre acoustics as well as sound equipment. THX (named after Lucas' first feature film,
THX 1138) is a sound system designed specifically to reproduce film sound exactly as it
was recorded by the filmmaker.
The THX Sound System is the only program of its kind to consider all aspects of a
theatre's audio & visual performance, including architecture, acoustics and equipment.
"THX is really a performance criteria; it's not a specific set of components," says
Holman. The system was created to complement advances made by Dolby Laboratories in
decoding sounds in the sound track which concentrates on the "A-Chain." The THX Sound
System concentrates on the "B-Chain" of a theatre's sound
system. The "B-Chain" is comprised of customized acoustical design work for each
auditorium, a special screen speaker installation method, a proprietary electronic
crossover network, and rigorous audio equipment specifications and performance standards.
Upon completion of a THX Sound System installation, the theatre is tested by a THX engineer
to make sure it meets both THX environmental technical criteria and recommended industry
standards for high quality visual and sound presentation. Theatres are recertified to
ensure that optimum quality is maintained.
A certified THX theatre carries several important advantages for the movie-goer. The
audience enjoys a more naturally balanced sound that uniformly reaches every seat in the
auditorium, improved dialog intelligibility and decreased bass distortion. Better stereo
localization makes the sound appear to travel across the screen with action. A frequency
range that is wider by a full octave in both bass and treble allows patrons to hear higher
highs and lower lows. The combined result is the reproduction of the same clear, dynamic
sound originally created by the filmmaker.
The exhibitor's unique challenge is to create an environment that keeps the magic of
the big screen alive. With installations in more than 1400 certified THX theatres and
dubbing facilities worldwide, the THX Sound System has become the premium standard for
quality film presentations.
Component Video
A DVD's picture information is stored as several separate picture elements: Luminance
(or brightness),
and Red
and Blue picture information (Y R-Y B-Y). Transmitting these picture elements
separately eliminates artifacts that might occur were they stored together as a
composite
signal. Composite video signals must be separated into their separate picture components by the
television, with variable and unpredictable
results. Component video inputs/outputs use three conventional
RCA/coaxial cables, and are currently the
highest quality video connection available between a DVD player and television. If your
television
or DVD player does not include component video
inputs or outputs, S-Video cabling should be used instead, with composite RCA/RF as a
last resort.
S-Video (Separate Video)
S-Video cable carries luminance, or brightness (Y) and color (C) information separately,
rather than as a composite signal (in which all brightness and color information is
blended together). When transmitted together, color and brightness information
must be extracted from one another by the television, often resulting in picture
artifacts such as 'dot crawl' and color bleeding. When used with a DVD player, S-Video
cables provide a dramatic improvement in picture quality over
composite RCA connections, and should be used if component video connection is not possible.
Rear Projection Television (RPTV)
Large televisions, ranging in size from 40-80 inches (diagonal
screen size), RPTVs are ideally suited for those wanting a
large picture without the hassle and expense of a front projection system. Higher quality
RPTVs include 3-D digital comb filters, which are used to eliminate dot crawl and hanging
dots. Some form of digital comb filter is highly recommended.
If your RPTV is to be used primarily for movie watching, you may want to consider a
Widescreen RPTV (see Anamorphic).
Front Projection Television FPTV
FPTVs project extremely large images, up to a practical maximum size of approximately
20 feet (diagonal screen size). Front projection televisions come in two varieties:
LCD (liquid crystal display) and CRT (cathode ray tube). CRTs are more expensive,
but tend to produce better and brighter pictures. CRT FPTVs should be professionally installed
and calibrated for your room and screen type/size, and readjusted every
six months to two years. LCD front projectors do not require regular readjustment after
they are
installed, and only a simple bulb change every now and then.
There are three grades of CRT projectors, each determined by their horizontal scan
rates (the number of lines the projector can draw across the screen in one second).
Video grade projectors scan at 15.75kHz and are the least expensive CRT models. Data grade
projectors scan at 31.5kHz and above, and can be used with a line doubler (see next
paragraph). Graphics grade models are the highest quality projectors, and can scan at 63kHz
and above. These projectors can be used with either a line doubler or a line quadrupler.
The numbers of pixels determines the quality of an LCD projector: the higher the better.
A line doubler significantly improves picture quality from conventional interlaced
video sources. A television picture is
made up of horizontal lines. One field contains the even numbered lines and the other
field contains the odd number lines. This process is called interlace scan. A line
doubler doubles the number of lines present at any one time. The line doubler holds one field in
memory and then spits
it out at the same time as the next field. This is called progressive scan and is used in
computer monitors. The horizontal scan lines disappear and the picture looks more film-like.
The biggest difference among projection screens is the gain. The gain is a
measurement for the
amount of light a screen reflects. Some screens are perforated in order to hide speakers.
Screens can be mounted on a wall, lowered from the ceiling manually or by motor, and can
be placed on a stand.
High Definition Television (HDTV)
The FCC describes HDTV as follows: "High Definition Television offers approximately twice the
vertical and horizontal resolution of NTSC, which is a picture quality approaching 35 mm
film and has a sound quality approaching that of a compact disc."
Direct Broadcast Satellite (DBS) / Direct Satellite System (DSS)
DSS uses a small 18 inch dish and a VCR sized receiver. As many as 200 channels
of sports, music and movies can be viewed, with audio and video quality that rivals LD.
Six Channel Discrete Inputs
Six-channel discrete inputs provide a cheap upgrade path for six-channel
audio systems. Lower cost amplifiers without DTS or Dolby Digital processing often include
six-channel discrete inputs, allowing DVD players with appropriate onboard processing
to mate directly with the receiver/amp's amplification stage. Six-channel inputs
also ensure compatibility with
future six-channel audio formats, such as DVD-Audio and SACD, and less common formats such as
MPEG Multichannel.
Digital Signal/Soundfield Processing (DSP)
DSP systems attempt to recreate the sonic characteristics of a live venue. This
often involves the use of
artificial echoes, reverberations and the
alteration of various audio frequencies. DSP modes are common on many home theater
receivers, amplifiers and processors, working with varying degrees of success.
Common DSP settings include 'Hall', 'Stadium', 'Jazz Club', and 'Theater'.
Although capable of producing interesting results, few DSP systems recreate live venues
with any accuracy.
Some listeners enjoy DSP modes, but most audiophiles prefer regular stereo, Dolby
Digital, DTS or Pro Logic.
Anamorphic
Anamorphically-enhanced DVD transfers offer the highest picture quality
possible from the DVD format. Essentially, a conventional widescreen image is
compressed horizontally when transferred to DVD, and uncompressed upon playback by a
widescreen television or video projector. This process increases the image's vertical
resolution by 33%, and nearly eliminates visible scan lines. On a standard 4:3 television,
the film will be horizontally compressed, with actors and scenery appearing tall
and thin. To compensate for this effect on 4:3 televisions, DVD players remove
every fourth vertical line and place black bars above and below the resultant active image
(this technique is called anamorphic downconversion).
The result is an image that appears normal on standard televisions.
Different players perform this task with varying degrees of success. Simply discarding every
fourth line will result in a sharp image, but with obvious aliasing and video artifacts,
while more sophisticated digital interpolation techniques
eliminate these artifacts, but may produce an image that appears subjectively soft.
DVD-18
A DVD-18 DVD is a dual-sided, dual-layered DVD, allowing up to eight hours of high
quality audio and video to fit on a single disc. A DVD-18 disc is functionally
identical to two DVD-9 (single-sided, dual layer)
RSDL discs glued back-to-back, but requires a much more delicate construction technique.
Conventional dual-layer DVDs store one layer of data
on each side of the disc; the DVD player's laser simply changes focus at the end of the
first side, and begins reading the second side (through the transparent
glue used to bond the two layers together). Unlike DVD-9 discs, the two layers on each
side of a DVD-18 are not located on opposite sides of the disc. The first layer of data is
actually embedded within the disc's upper polycarbonate substrate
(plastic surface layer), while the second
layer is located where the first layer would normally be found on a conventional DVD-9 disc.
This process requires much more care when manufacturing than conventional DVDs, making
DVD-18s more expensive
to produce than conventional single-sided single-layer (DVD-5) or single-sided dual-layer
(DVD-9) DVDs. The first DVD-18 released in North America was Artisan's The Stand.
RSDL
RSDL stands for 'Reverse Spiral Dual Layer'. An RSDL disc uses two layers of information
stored on opposite sides of a DVD disc; both of which can be read from only one side of the
disc. The DVD player reads the first layer (layer 0) from the
center of the disc out. When the laser approaches the outer edge of the
disc, it changes focus onto the second layer, and
begins to read the second layer (layer 1) from the disc's outer edge toward the center
of the disc.
RSDL discs permit much more information to be stored on one 'side' of a DVD, allowing longer
films to play uninterrupted, and higher video bit-rates to be used. When a DVD player
changes
layer, there may be a slight pause as the player finds the beginning of the second layer. The
first RSDL disc released in North America was Artisan's Terminator 2: Judgment Day.
Progressive Scan
Conventional interlaced television systems display one low quality video 'field' 50 to 60
times every second. Combined together, two fields make a single, perceptually higher quality,
'frame'. These fields/frames are shown so rapidly that the eye is fooled into believing it
is viewing a high quality moving image, not a succession of low resolution still images.
A progressive scan DVD player reconstructs complete frames from a DVD, and does not output
individual low quality fields. The result is a more natural, stable image, with fewer
interlacing artifacts such as shimmering and flicker. Progressive scan systems also more
accurately recreate films as they are projected theatrically: as complete frames, not
fields.
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