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D1:
A format for component digital video tape recording working to the
ITUR 601, 4:2:2 standard using
8-bit sampling. The tape is 19 mm wide and allows up to 94 minutes to
be recorded on a cassette. Being a component recording system it is
ideal for studio or post production work with its high chrominance
bandwidth allowing excellent chroma keying. Also multiple generations
are possible with very little degradation and D1 equipment can
integrate without transcoding to most digital effects systems,
telecines, graphics devices, disk recorders, etc. Being component
there are no color framing requirements. Despite the advantages, D1
equipment is not extensively used in general areas of TV production,
at least partly due to its high cost. (Often used incorrectly to
indicate component digital video.)
D2:
The VTR standard for digital composite (coded) NTSC or PAL signals
that uses data conforming to SMPTE 244M. It uses 19 mm tape and
records up to 208 minutes on a single cassette. Neither cassettes nor
recording formats are compatible with D1. D2
has often been used as a direct replacement for 1-inch analog VTRs.
Although offering good stunt modes and multiple generations with low
losses, being a coded system means coded characteristics are present.
The user must be aware of cross-color, transcoding footprints, low
chrominance bandwidths and color framing sequences. Employing an 8-bit
format to sample the whole coded signal results in reduced amplitude
resolution making D2 more susceptible to contouring artifacts. (Often
used incorrectly to indicate composite digital video.)
D3:
A composite digital video recording format that uses data conforming
to SMPTE 244M. Uses 1/2-inch tape cassettes for recording digitized
composite (coded) PAL or NTSC signals sampled at 8 bits. Cassettes are
available for 50 to 245 minutes. Since this uses a composite signal
the characteristics are generally as for D2 except that the 1/2-inch
cassette size has allowed a full family of VTR equipment to be
realized in one format, including a camcorder.
D4: A
format designation never utilized due to the fact that the number four
is considered unlucky (being synonymous with death in some Asian
languages).
D5: A
VTR format using the same cassette as D3 but recording component
signals conforming to the ITU-R BT.601-2 (CCIR 601) recommendations at
10-bit resolution. With internal decoding D5 VTRs can play back D3
tapes and provide component outputs.
Being a non-compressed component digital
video recorder means D5 enjoys all the performance benefits of D1,
making it suitable for high-end post production as well as more
general studio use. Besides servicing the current 625 and 525 line TV
standards the format also has provision for HDTV recording by use of
about 4:1 compression (HD D5). See also: HD D5.
D6:
A digital tape format which uses a 19mm helical-scan cassette tape to
record uncompressed high definition television material at 1.88 GBps
(1.2 Gbps). D6 is currently the only high definition recording format
defined by a recognized standard. D6 accepts both the European 1250/50
interlaced format and the Japanese 260M version of the 1125/60
interlaced format which uses 1035 active lines. It does not accept the
ITU format of 1080 active lines. ANSI/SMPTE 277M and 278M are D6
standards.
D7:
DVCPRO. Panasonic's development of native DV component format which
records a 18 micron (18x10-6m, eighteen thousandths of a millimeter)
track on 6.35 mm (0.25-inch) metal particle tape. DVCPRO uses native
DCT-based DV compression at 5:1 from a 4:1:1 8-bit sampled source. It
uses 10 tracks per frame for 525/60 sources and 12 tracks per frame
for 625/50 sources, both use 4:1:1 sampling. Tape speed is 33.813mm/s.
It includes two 16-bit digital audio channels sampled at 48 kHz and an
analog cue track. Both Linear (LTC) and Vertical Interval Time Code (VITC)
are supported. There is a 4:2:2 (DVCPRO50) and progressive scan 4:2:0
(DVCPRO P) version of the format, as well as a high definition version
(DVCPROHD). See also: DVCPRO50, DVCPROHD, DVCPRO P.
D8:
There is no D8. The Television Recording and Reproduction Technology
Committee of SMPTE decided to skip D8 because of the possibility of
confusion with similarly named digital audio or data recorders
(DA-88).
D9 (Formerly
Digital-S): A 1/2-inch digital tape format developed by JVC
which uses a high-density metal particle tape running at 57.8mm/s to
record a video data rate of 50 Mbps. The tape can be shuttled and
search up to 32x speed. Video sampled at 4:2:2 is compressed at 3.3:1
using DCT-based intra-frame compression (DV). Two or four audio
channels are recorded at 16-bit, 48 kHz sampling; each is individually
editable. The format also includes two cue tracks. Some machines can
play back analog S-VHS. D9 HD is the high definition version recording
at 100 Mbps.
D9 HD:
A high definition digital component format based on D9. Records on
1/2-inch tape with 100 Mbps video.
D16: A
recording format for digital film images making use of standard D1
recorders. The scheme was developed specifically to handle Quantel's
Domino (Digital Opticals for Movies) pictures and record them over the
space that sixteen 625 line digital pictures would occupy. This way
three film frames can be recorded or played every two seconds. Playing
the recorder allows the film images to be viewed on a standard
monitor; running at 16x speed shows full motion direct from the tape.
DA-88:
A Tascam-brand eight track digital audio tape machine using the 8 mm
video format of Sony. It has become the de facto standard for audio
post production though there are numer ous other formats, ranging from
swappable hard drives to analog tape formats and everything in
between.
DAC
(D-A, D/A, D-to-A): Digital-to-analog converter. See
also: ADC.
Data compression: A
technique that provides for the transmission or storage, without
noticeable information loss, of fewer data bits than were originally
used when the data was created.
Data recorders: Machines
designed to record and replay data. They usually include a high degree
of error correction to ensure that the output data is absolutely
correct and, due to their recording format, the data is not easily
editable. This compares with video recorders which will conceal
missing or incorrect data by repeating adjacent areas of picture and
which are designed to allow direct access to every frame for editing.
Where data recorders are used for recording video there has to be an
attendant "workstation" to see the pictures or hear the
sound, whereas VTRs produce the signals directly. Although many data
recorders are based on VTRs' original designs, and vice versa, VTRs
are more efficient for pictures and sound while data recorders are
most appropriate for data.
dB (decibel): A
measure of voltage, current, or power gain equal to 1/10 of a bel.
Given by the equations 20 log Vout/Vin, 20 log Iout/Iin, or 10 log
Pout/Pin. See also: Bel.
DBS: Digital
broadcast system. An alternative to cable and analog satellite
reception initially utilizing a fixed 18-inch dish focused on one or
more geostationary satellites. DBS units are able to receive multiple
channels of multiplexed video and audio signals as well as programming
information, Email, and related data. DBS typically uses MPEG-2
encoding and COFDM transmission. Also known as digital satellite
system.
D-Cinema (also
E-Cinema): Digital cinema.
Typically the process of using video at 1080/24p instead of film for
production, post production and presentation.
DCT: 1.
Discrete cosine transform. A widely used method of data compression of
digital video pictures basically by resolving blocks of the picture
(usually 8 x 8 pixels) into frequencies, amplitudes, and colors. JPEG
and DV depend on DCT. 2. Also an Ampex data videotape format using
discrete cosine transform.
DD2:
Using D2 tape, data recorders have been developed offering (by
computer standards) vast storage of data (which may be images). A
choice of data transfer rates is available to suit computer
interfaces. Like other computer storage media, images are not directly
viewable, and editing is difficult.
DDR: Digital
disk recorder. See: Disk recorder.
DDS: Digital
data service.
Demultiplexing:
Separating elementary streams or individual channels of data from a
single muti-channel stream. For example, video and audio streams must
be demultiplexed before they are decoded. This is true for multiplexed
digital television transmissions. See also: Multiplex.
DEMUX:
Demultiplexer. See: Demultiplexing.
Deserializer: A
device that converts serial digital information to parallel digital.
Desktop video: Video
editing and production done using standard desktop computing platforms
running add-on video hardware and software.
D/I:
Drop and insert. A point in the transmission where portions of the
digital signal can be dropped out and/or inserted.
Diagnostics:
Tests to check the correct operation of hardware and software. As
digital systems continue to become more complex, built-in automated
testing becomes an essential part of the equipment. Some extra
hardware and software has to be added to make the tests operate.
Digital systems with such provisions can often be quickly assessed by
a trained service engineer, so speeding repair.
Digital:
Circuitry in which data carrying signals are restricted to either of
two voltage levels, corresponding to logic 1 or 0. A circuit that has
two stable states: high or low, on or
off.
Digital Betacam:
A development of the original analog Betacam VTR which records
digitally on a Betacam-style cassette. It uses mild intra-field
compression to reduce the ITU-R 601 sampled video data by about 2:1.
Some models can replay both digital and analog Betacam cassettes.
Digital
chromakeying: Digital chromakeying
differs from its analog equivalent in that it can key uniquely from
any one of the 16 million colors represented in the component digital
domain. It is then possible to key from relatively subdued colors,
rather than relying on highly saturated colors that can cause
color spill problems on the foreground. A high-quality digital
chromakeyer examines each of the three components of the picture and
generates a linear key for each. These are then combined into a
composite linear key for the final keying operation. The use of three
keys allows much greater subtlety of selection than does a
chrominance-only key Digital components: Component video signals that
have been digitized.
Digital disk
recorder (DDR):
A video recording device that uses a hard disk drive or optical disk
drive mechanism. Disk recorders offer nearly instantaneous access to
recorded material. Digital effects: Special effects created using a
digital video effects (DVE) unit.
Digital parallel
distribution amplifier: A
distribution amplifier designed to amplify and fan-out parallel
digital signals.
Digital-S:
See: D9.
Digital word:
The number of bits treated as a single entity by the system.
Digitizing
time: Time taken to record footage
into a disk-based editing system,
usually from a tape-based analog system, but also from newer digital
tape formats without direct digital connections.
Distribution
quality: The level of
quality of a television signal from the station to its viewers. For
digital television this is approximately 19.39 Mbps.
Dither:
A form of smart conversion from a higher bit depth to a lower bit
depth, used in the conversion of audio and graphic files. In the
conversion from 24-bit color to 8-bit color (millions of colors
reduced to 256), the process |
attempts to improve on
the quality of on-screen graphics with reduced color palettes by
adding patterns of different colored pixels to simulate the original
color. The technique is also known as "error diffusion," and
is applied to audio bit rate reduction and graphic resolution.
DNG:
Digital news gathering. Electronic news gathering (ENG) using digital
equipment and/or transmission.
Dolby Digital
(formerly Dolby AC-3): The approved 5.1 channel
(surround-sound) audio standard for ATSC digital television, using
approximately 13:1 compression Six discrete audio channels are used:
Left, Center, Right, Left Rear (or side) Surround, Right Rear
(or side) Surround, and a subwoofer (considered the ".1" as
it is limited in bandwidth). The bit rate can range from 56 kbps to
640 kbps, typically 64 kbps mono, 192 kbps two-channel, 320 kbps 35mm
Cinema 5.1, 384 kbps Laserdisc/DVD 5.1 and ATSC, 448 kbps 5.1. When
moving from analog recording to a digital recording medium, the
digital audio coding used yields an amount of data often too immense
to store or transmit economically, especially when multiple channels
are required. As a result, new forms of digital audio coding--often
known as "perceptual coding"--have been developed to allow
the use of lower data rates with a minimum of perceived degradation of
sound quality. Dolby's third generation audio coding algorithm
(originally called AC-3) is such a coder. This coder has been designed
to take maximum advantage of human auditory masking in that it divides
the audio spectrum of each channel into narrow frequency bands of
different sizes, optimized with respect to the frequency selectivity
of human hearing. This makes it possible to sharply filter coding
noise so that it is forced to stay very close in frequency to the
frequency components of the audio signal being coded. By reducing or
eliminating coding noise wherever there are no audio signals to mask
it, the sound quality of the original signal can be subjectively
preserved. In this key respect, a coding system like Dolby Digital is
essentially a form of very selective and powerful noise reduction.
Dolby E: A
new coding system designed specifically for use with video available
from Dolby Laboratories. The audio framing is matched to the video
framing, which allows synchronous and seamless switching or editing of
audio and video without the introduction of gaps or A/V sync
slips. All of the common video frame rates, including 30/29.97, 25,
and 24/23.976, can be supported with
matched Dolby E audio frame sizes. The Dolby E coding technology is
intended to provide approximately 4:1 reduction in bit rate. The
reduction ratio is intentionally limited so that the quality of the
audio may be kept very high even after a number of encode-decode
generations. The fact that operations such as editing and switching
can be performed seamlessly in the coded
domain allows many coding generations to be avoided,
further increasing quality. A primary carrier for the Dolby E data
will be the AES/EBU signal. The Dolby E coding
will allow the two PCM audio channels to be replaced with eight
encoded audio channels. A VTR PCM track pair will become capable of
carrying eight independent audio channels, plus the accompanying
metadata. The system is also intended to be applied on servers and
satellite links. A time delay when encoding or decoding
Dolby E is unavoidable. In order to facilitate the provision of a
compensating video delay, the audio encoding and decoding delay have
been fixed at exactly one frame. When applied with video recording
formats which incorporate frame based video encoding, it can be
relatively easy to provide for equal video and audio coding delays.
When applied with uncoded video, it may be necessary to provide a
compensating one frame video delay.
Dolby Surround
(Dolby Stereo, & Dolby 4:2:4):
Matrix Analog coding of four audio channels--Left, Center, Right,
Surround (LCRS), into two channels referred to as Right-total and
Left-total (Rt, Lt). On playback, a Dolby Surround Pro Logic decoder
converts the two channels to LCRS and, optionally, a subwoofer
channel. The Pro Logic circuits are used to steer the audio and
increase channel separation. The Dolby Surround system, originally
developed for the cinema, is a method of getting more audio channels
but suffers from poor channel separation, a mono limited bandwidth
surround channel and other limitations. A Dolby Surround track can be
carried by analog audio or linear PCM, Dolby Digital and MPEG
compression systems. Down converting: The process which changes the
number of pixels and/or frame rate and/or scanning format used to
represent an image by removing pixels. Down converting is done from
high definition to standard definition. See also: Side converting, up
converting.
DQPSK:
Differential quadrature phase shift keying. DQPSK is a digital modulation
technique commonly used with cellular systems. Motorola's CyberSurfr
cable modem uses DQPSK to carry data upstream from the subscriber's
computer to the Internet on a narrower frequency band than standard
QPSK. Narrower bands allow more upstream channels, so the CyberSurfr
has additional noise-free channels to choose from when it's installed.
DRAM:
Dynamic RAM (Random Access Memory). High density, cost effective memory
chips (integrated circuits). Their importance is such that the
Japanese call them the "rice of electronics." DRAMs are used
extensively in computers and generally in digital circuit design, but
also for building frame stores and animation stores. Being solid state,
there are no moving parts and they offer the densest available
method for accessing or storing data. Each bit is stored on a
single transistor, and the chip must be powered and clocked to retain
data.
DS0: Digital
signal level zero, 64 kbps.
DS1:
A telephone company format for transmitting information digitally. DS1
has a capacity of 24 voice circuits at a
transmission speed of 1.544 megabits per second. See also: T1.
DS3: A
terrestrial and satellite format for transmitting information
digitally. DS3 has a capacity of 672 voice circuits at a transmission
speed of 44.736 Mbps (commonly referred
to as 45 Mbps). DS3 is used for digital television distribution using
mezzanine level compression--typically MPEG-2 in nature, decompressed
at the local station to full bandwidth signals (such as HDTV) and then
re-compressed to the ATSC's 19.39 Mbps transmission standard.
DSL:
Digital subscriber line. The ability to use a standard telephone line
to transport data. xDSL is the generic term for each of two varieties:
ADSL (asynchronous), where the upstream and downstream data rates are
different, and SDSL (synchronous), where the upstream and downstream
data rates are the same.
DSS:
Digital satellite system. Due to trademark issues, the abbreviation is
no longer used. See DBS.
DTT:
Digital terrestrial television. The term used in Europe to describe
the broadcast of digital television services using terrestrial
frequencies.
DTV Team, The: Originally
Compaq, Microsoft and Intel, later joined by Lucent Technologies. The
DTV Team promotes the computer industry's views on digital
television--namely, that DTV should not have interlace scanning
formats but progressive scanning formats only. (Intel, however, now
supports all the ATSC Table 3 formats, including those that are
interlace, such as 1080i.) Internet: www.dtv.org.
DV:
This digital VCR format is a cooperation between Hitachi, JVC, Sony,
Matsushita, Mitsubishi, Philips, Sanyo, Sharp, Thomson and Toshiba. It
uses 6.35 mm (0.25-inch) wide tape in a range of products to record
525/60 or 625/50 video for the consumer (DV) and professional markets
(Panasonic's DVCPRO, Sony's DVCAM and Digital-8). All models use
digital intra-field DCT-based "DV" compression (about 5:1)
to record 8-bit component digital video based on 13.5 MHz luminance
sampling. The consumer versions, DVCAM, and Digital-8 sample video at
4:1:1 (525/60) or 4:2:0 (625/50) video (DVCPRO is 4:1:1 in both 525/60
and 625/25) and provide two 16-bit/48 or 44.1 kHz, or four 12-bit/32
kHz audio channels onto a 4 hour 30 minutes standard cassette or
smaller 1 hour "mini" cassette. The video recording rate is
25 Mbps.
DVB:
Digital video broadcasting. The group, with over 200 members in 25
countries, which developed the preferred scheme for digital
broadcasting in Europe. The DVB Group has put together a satellite
system--DVB-S--that can be used with any transponder, current or
planned, a matching cable system--DVB-C, and a digital terrestrial
system--DVB-T. Internet: www.dvb.org. See also: DVB-T.
DVB-T: The
DVB-T is a transmission scheme for terrestrial digital television. Its
specification was approved by ETSI in February 1997 and DVB-T services
began in 1998. As with the other DVB standards, MPEG-2 sound and
picture coding form the basis of DVB-T. It uses a transmission scheme
based on Coded Orthogonal Frequency Division Multiplexing (COFDM),
which spreads the signals over a large number of carriers to enable it
to operate effectively in very strong multipath environments. The
multipath immunity of this approach means that DVB-T can operate an
overlapping network of transmitting stations with a single frequency.
In the areas of overlap, the weaker of the two received signals is
rejected. See also: COFDM, DVB. DVCAM: Sony's development of native DV
which records a 15 micron (15x10-6m, fifteen thousandths of a
millimeter) track on a metal evaporated (ME) tape. DVCAM uses DV
compression of a 4:1:1 signal for 525/60 (NTSC) sources and 4:2:0 for
625/50 (PAL). Audio is recorded in one of two forms--four 12-bit
channels sampled at 32 kHz, or two 16-bit channels sampled at 48 kHz.
DVCPRO: See: D7.
DVCPRO50: This
variant of DV uses a video data rate of 50 Mbps--double that of other
DV systems--and is aimed at the higher quality end of the market.
Sampling is 4:2:2 to give enhanced chroma resolution, useful in post
production processes (such as chromakeying). Four 16-bit audio tracks
are provided. The format is similar to Digital-S (D9).
DVCPRO HD:
This variant of DV uses a video data rate of 100 Mbps--four times that
of other DV systems--and is aimed at the high definition EFP end of
the market. Eight audio channels are supported. The format is similar
to D9 HD.
DVCPRO P:
This variant of DV uses a video data rate of 50 Mbps--double that of
other DV systems--to produce a 480 progressive picture. Sampling is
4:2:0.
DVD:
Digital versatile disk: A high density development of the compact
disk. It is the same size as a CD but stores from 4.38 GB (seven times
CD capacity) on a single sided, single layer disk. DVDs can also be
double sided or dual layer-storing even more data. The capacities
commonly available at present:
DVD-5:
4.7 GB (1 side, 1 layer)
DVD-9:
8.5 GB (1 side, 2 layers)
DVD-10:
9.4 GB (2 sides, 1 layer each)
DVD-18:
17.0 GB (2 sides, 2 layers)
DVD-R:
4.7 GB (1 side, 1 layer) (write once)
DVD-RAM:
2.6 GB (per side, 1 layer) (rewritable)
DVD-RAM:
4.7 GB (per side, 1 layer) (rewritable)
DVE:
Digital video effects. A registered trademark of Nippon Electric
Company. Refers to video equipment that performs digital effects such
as compression and transformation.
DVTR:
Digital videotape recorder.
Dynamic
Rounding: The intelligent truncation of digital signals. Some
image processing requires that two signals are multiplied, for example
in digital mixing, producing a 16-bit result from two original 8-bit
numbers (see: Byte). This has to be truncated, or rounded, back to
8-bits. Simply dropping the lower bits can result in visible
contouring artifacts especially when handling pure computer generated
pictures. Dynamic Rounding is a mathematical technique for truncating
the word length of pixels--usually to their normal 8-bits. This
effectively removes the visible artifacts and is non-cumulative on any
number of passes. Other attempts at a solution have involved
increasing the number of bits, usually to 10, making the LSBs (least
significant bit) smaller but only masking the problem for a few
generations. Dynamic Rounding is a licensable technique, available
from Quantel and is used in a growing number of digital products both
from Quantel
and other manufacturers.
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