2/23/18
An
HDTV Primer
Please report any suggestions
or errors of fact that you find to the author at kq6qv@aol.com. Author: Ken Nist, MSEE (ret), KQ6QV
This website is unaffiliated and unfunded and accepts no advertising.
This
web site was created in 2003 to help nontechnical people cope with the digital
transition. The transition is now
history, and with it much of the reason for this site.
The
unique parts of the web site have been left up. The site will continue to track new
developments in over-the-air TV antennas.
Issues:
Other resources:
To
find information about a particular product, just Google the model number. There is a useful collection of product
reviews at eCoustics.com. (Product reviews of HDTVs by
amateurs are not reliable.)
If,
after all the study, you still need some questions answered, then online
forums are available. The Audio
Visual Science Forum, AVSforum,
is the oldest, largest, and most active forum devoted to TV and home
theater. However this forum is not
intended for amateurs, and HDTV newcomers often find its size and structure a
bit imposing. The HDTV Magazine forum is
simpler and friendlier. A number of
experts hang out on both of these forums.
Both have a huge wealth of answered questions. It is unlikely that your question has
not been asked before, so you should start out with a search by keywords. Both forums require you to invent a
screen name and password in order to post a question or answer, but there are
no fees or other hassles.
Glossary: (optional
reading)
ATSC (Advanced
Television System Committee technical standard)
CEC (Consumer Electronics Control)
DBS
(direct broadcast satellites)
D-ILA (Direct-drive
Image Light Amplifier) (see LCOS)
DTCP (Digital Transmission Content
Protection)
DVB (Digital Video Broadcasting)
DVI (Digital Visual Interface)
FCC (Federal Communications Commission)
FTA
(Free To All MPEG-2 broadcasts)
HAVi (Home Audio Video Interoperability)
HDCP (High-bandwidth Digital Content
Protection)
HDMI (High-Definition
Multimedia Interface)
LCOS (Liquid Crystal On Silicon)
LNB
(Low Noise Block converter)
Motion Adaptive
De-interlacing
MPEG-2
(Motion Picture Experts Group technical standard 2)
MTS (Multi-channel Television Sound)
NTSC
(National Television System Committee technical standard)
PAL
(Phase Altering Line standard)
SECAM (Sequential Color And Memory standard)
SPDIF (Sony/Philips Digital Interface)
AACS Advanced Access Control System. A computer specification
for guarding next-generation optical-media content created by the film, electronics,
and software industries.
AC-3 (see Dolby Digital
5.1)
Aliasing – Jaggedness that appears at
diagonal edges of objects in a pixel or raster image. De-aliasing
(anti-aliasing) is a smoothing of the jagged edges by blending adjacent
pixels slightly.
Artifact – A flaw in an image caused by
the way the data is processed.
Interference and noise are not usually called artifacts. So artifacts are in a sense predictable.
Aspect ratio The ratio of screen width to screen
height. For TVs it is either 4:3
(1.33:1) or 16:9 (1.78:1). Theater
film uses many different aspect ratios, some as high as 2.5:1.
ATSC (Advanced Television Systems Committee technical standard) This is the name of the technology used by terrestrial digital TV stations in the U.S.
Blocking,
Macro-blocking An over-compression of the image that
makes the block edges slightly noticeable.
This “checkerboarding” often covers the whole screen. It is subtle and usually momentary. Some causes are:
1.
Software
bugs in the MPEG encoder.
2.
The
network allocating too little bandwidth to the broadcast.
3.
The
picture being portrayed is just changing too fast.
Blocks, Macro-blocks MPEG-2
divides the screen into small square regions called blocks and uses a
mathematical process to compress the data for each block. Macro-blocks are a small group of
blocks. See What
exactly is ATSC? .
BNC connectors These common RF connectors are sometimes found on VGA cables in place of a VGA connector. They employ a quarter-turn twist-lock mechanism.
Bob and Weave Two processes for de-interlacing (converting interlaced video into progressive scan). Weave refers to combining successive fields. Also called interfield, this method preserves the original resolution. Bob refers to up-converting a field into a frame, in effect creating new lines by averaging the adjacent lines above and below. Also called intrafield, this method causes a loss of resolution but never causes motion artifacts. See also Motion Adaptive De-interlacing.
Breakup Also called dropouts, block errors, or macro-block errors, these are gross errors in the picture caused by reception errors that result from interference and signal noise. Both audio and video are affected, with video distortions about five times as prevalent as audio dropouts. This ratio never seems to change. If the ratio is anything else then the cause is a network problem, not a reception error. The shortest-lasting breakups just cause a few macro-blocks to be obviously wrong, while more severe errors cause major parts of the screen to be left un-updated for a time, and possibly the whole image to freeze. Green shows up a lot.
Cable card The
Cable Card is the mechanism the industry has adopted to prevent the piracy of
cable services. Nearly all cable
channels are encrypted, the main exception being local stations. The cable card contains the keys to
unlock encryption.
If you want the simplicity that comes with the cable receiver being integrated with the TV then you should buy a TV with a cable card slot. However if you like TiVo then you would instead get a DVR, which will have its own cable card slot. The cable card is supplied by the cable company. The card is a special purpose PCMCIA card (like used in many computers).
The present cable card system for DTV is called CableCARD 1.0. There are two types of cards: SCards (single stream) and MCards (multiple stream). MCards are used when a DVR can record multiple programs simultaneously.
CableCARD 1.0 lacks two-way features and cannot be used for ordering pay-per-view, interactive guide, and other two-way features. Millions of cable card slots in TVs already sold are going unused. Reasons include: 1. The viewer uses satellite. 2. The viewer doesn’t want subscription channels. 3. The user wants two-way features and so has to use a cable box. Some TV makers are reducing the number of sets they sell having cable card slots, but they say they will increase the number when two-way is possible. Two-way is not available because the technical standard is not yet established. (The CEA and NCTA are fighting each other and the FCC has been a timid referee.) Present DTV systems with CableCARD 1.0 are labeled DCR (Digital Cable Ready). Future DTVs will likely be labeled iDCR (Interactive Digital Cable Ready).
Warning: The term CableCARD 2.0 has two conflicting definitions. 1. CableCARD 2.0 was first used to refer to the next generation of cable services that included two-way features. 2. SCards were introduced first. Later, when MCards were introduced they were commonly referred to as CableCARD 2.0.
C-band / Ku-band 1. a range of RF spectrum. C-band is approximately 4 GHz. Ku-band is app. 12 GHz. 2. Geo-stationary satellites the networks use to acquire and distribute programming to affiliates and cable TV companies. These satellites use C-band and Ku-band frequencies. 3. a consumer service that uses the satellites the networks originally set up for themselves. An 8-foot steerable dish is required. Some channels are free. Others are available by subscription. The digital channel subscription service is called 4DTV.
CEC (Consumer Electronics Control) This feature allows units to control
each other. The commands tend to be
the same as the buttons of an infrared remote control, so fewer remotes are
necessary. The implementation is a
single-wire bus that is a “party line” connecting to all
units. The HDMI cable carries this
line.
COFDM modulation
technique. This technical standard
has been used in Europe and other places for digital TV. 8VSB is used in the U.S.
Color temperature This describes how white is
displayed. Low temperature means
slightly reddish, while high temperature means slightly bluish. Standard NTSC white corresponds to the
color a glowing hot object would be at 6500° K
Comb filter
A circuit in NTSC sets that separates the color information from the
brightness information.
Component
video This 3-wire convention was originally
created for connecting DVD players to TVs or monitors. It avoids downgrading the signal to
NTSC. The signals may be RGB or
YPrPb. Some HD STBs have only
component video output.
Composite
video This 1-wire standard contains all video
information: intensity, color, and sync.
The encoding is the same as NTSC, and thus has the “overlapping
sideband” problem which sometimes causes wrong colors to appear.
Convergence
An adjustment that must be made occasionally to CRT sets. This adjustment makes the three colors
coincide perfectly.
DBS (direct broadcast satellites) These satellites are powerful enough to be received by an 18 inch dish. They use Ku-band and Ka-band frequencies. Companies that provide DBS services to consumers in the U.S. are DirecTV and Dish Network. Canadian DBS providers are Star Choice and Bell ExpressVu. Also called DSS.
D-ILA (Direct-drive Image
Light Amplifier) (see LCOS)
DirecTV (see DBS)
Dish Network (see DBS)
DLP (digital light
processor). A technology for video projection,
also call DMD (Digital Micro-mirror Device). It is a large chip with about a million
tiny mirrors on its surface. The chip
can tilt each mirror to vary the amount of light reflected off of it.
Dolby
Digital 2.0 This is a two channel (stereo or Pro
Logic) version of Dolby Digital. It
is often used by DBS systems.
Dolby
Digital 5.1 Also known as AC-3, it provides 6 channels
of sound: left, center, right, left rear, right rear, and sub-woofer. It is also called “5.1
channels” since the 6th channel has reduced bandwidth. Dolby Digital 5.1 is the audio standard
for all U.S. digital TV stations, most DVDs, some DBS programs, and many
theaters.
Dolby
Pro Logic Surround This is a 4-channel
analog system. During recording,
the 4 channels are “folded” into 2 stereo channels. If played back without a Pro Logic
decoder, it sounds like normal stereo.
This format is becoming obsolete.
Dot Crawl a common flaw in NTSC
images caused by the “overlapping sidebands” problem. It consists of animated checkerboard
patterns which appear along vertical color transitions.
DTCP (Digital Transmission Content
Protection) This is an encryption
standard for IEEE 1394 that prevents the copying of first-run movies and
pay-per-view events. DTCP is also
called 5C Copy protection (in reference to the ‘five companies’
that license it).
DTS An alternative to
Dolby Digital. ATSC does not use DTS
but some DVDs do. Most audio
receivers that work with Dolby Digital also handle DTS.
DTV (digital TV). Examples of DTV are DBS satellite
services, digital cable TV services, and ATSC digital TV stations.
DTVLink This logo is on equipment that has IEEE
1394 and DTCP.
DVB (Digital Video Broadcasting) An alternative to ATSC used in most of
the world outside the U.S. It has
three different standards:
· DVB-T is for terrestrial (OTA)
broadcasts.
· DVB-S is for satellite
broadcasts.
· DVB-C is for cable broadcasts.
DVI (Digital Visual Interface) This
connector conveys HDTV image scanning signals in binary data form. The data rate is very high (1.65
Gb/s). Binary data is preferred by
monitors that are not CRTs. DVI
comes with a decryption option called HDCP which will decode encrypted programs
such as first-run movies.
EDTV (enhanced
definition TV) Essentially DVD
quality, it is a small step up from NTSC.
An EDTV will convert all 18 ATSC formats to 480p.
FCC (Federal Communications Commission) This
is a Federal agency responsible for regulating radio wave usage and some other
media. The FCC answers to Congress
and also implements international radio standards.
Fire-wire (see IEEE 1394)
First-surface mirror Normal mirrors have
the silvering on the back surface of the glass. First surface mirrors have it on the
front. Cleaning a first-surface
mirror must be done very carefully.
Flicker (or Twitter) Flicker is a pulsating of the image, a
flaw most noticeable in images drawn only 24 or 30 times per second. Flicker is only noticeable in large
bright white areas.
FTA “Free To Air” or “Free
To All”. This is a digital satellite
technology employing MPEG-2, but it is not compatible with DBS systems (Dish or DirecTV) or with Motorola Digicipher II (C-band 4DTV) and it
doesn’t have a provision for encryption. At the present time the only high
definition stations on FTA are PBS, NBC, Voom, The History Channel, and 4
Denver stations. Lyngsat.com lists
all the stations. Skyvision.com,
FTAsatellite.com, and others sell receivers. The frequencies used are Ku-band and
C-band. FTA’s forte is that
it is cheap and very international.
FTA is heavily used outside the U.S. FTA started becoming popular in the U.S.
about 2002 among experimenters and immigrants. In the opinion of some people the rise
of FTA is a mistake and HDTV might eventually kill it. It might survive in the U.S. market
because of a need for an unregulated domain for international stations.
GLV (Grating Light Valve) This is another contender to replace
CRTs in projection TVs.
HAVi (Home Audio Video Interoperability) This is a standard for 1394 bus audio and
video devices. It is software that is required for the
units to talk to each other. HAVi
allows plug-and-play recognition of devices, interoperability, and brand
independence.
HDCP (High-bandwidth Digital Content
Protection) This is a DVI decryption option. It will decode encrypted programs such
as first-run movies. (It’s
real function is to prevent unauthorized copying of programs.)
HD-Capable TV
A standard definition set with a digital tuner. (This term was probably invented to
confuse people.)
HD-Ready TV
An HDTV monitor or TV that lacks a digital tuner.
HDMI (High-Definition
Multimedia Interface) This miniature connector is intended
to replace DVI. It is backward
compatible with DVI, and an adapter will connect it to a DVI unit. It has 19 pins and carries DVI plus
digital audio. It also has a reverse data line (DDC) that allows the STB to
sense the monitor’s state and native formats, and a control line (CEC)
for system level control.
HDTV (High Definition
TV) A TV that displays 1280x720
pixels or better.
IEEE
1394 Also called Firewire or iLink. Originally a serial bus for PCs, 1394
may or may not become the interconnection standard for DTV products. It is competing with HDMI. IEEE 1394 is a spec for a hardware
interconnect plus a software shell.
But additional software, such as HAVi, is required for connected units
to actually talk to each other.
i.link (see IEEE 1394)
Interlaced scan Historically, TV CRTs
are interlaced, while computer CRTs are not. Interlaced means that the electron beam
skips every other horizontal line, filling in the missing lines on the next
pass. A frame is composed of 2
fields. One field is all of the odd
numbered lines, and the other field is all of the even numbered lines.
Ka band
A range of RF spectrum centered around 30 Gigahertz. Historically never used, DirecTV and
Dish Network are starting to launch satellites that use these frequencies. (The name comes from “above
K band”. K band is a long
established military band.)
Ku band
A range of RF spectrum centered around 12 Gigahertz. These were once the only frequencies
used by DirecTV and Dish Network. (The name
comes from “under K band”.)
LCD (Liquid Crystal Display) LCD is the most common flat panel
display technology.
LCOS (Liquid Crystal On Silicon) This is an LCD-like projection
technology.
LFE (Low Frequency Effects) Sub-woofer. The 6th channel in a 5.1
channel system.
Line Doublers This device converts
NTSC or 480i into 480p. Also called
a de-interlacer.
LNB (Low Noise Block
converter) An LNB can be found at
the focus point of a dish antenna.
It is a low noise amplifier that also converts the signal to a lower
frequency. (The original higher
frequency would not travel very far in ordinary coaxial cable.)
Mosquitoes Fuzzy dots that can appear near sharp edges in MPEG and JPEG
images, possibly looking like a swarm of mosquitoes. These artifacts are caused by
over-compression or over-enhancement of edges.
Motion Adaptive De-interlacing The image is divided into regions where
there is motion and where there is none.
Areas of the image without motion are de-interlaced using
“weave”, and areas with motion are de-interlaced using
“bob”. See Bob and
Weave.
MPEG-2 (Motion Picture
Experts Group technical standard 2)
This is a widely used standard for digital encoding of motion
pictures. It typically achieves a
50 to 1 compression of data. It achieves this mainly by not retransmitting areas
of the screen that have not changed since the previous frame.
MTS (Multi-channel Television Sound) This refers to an analog NTSC TV
equipped with stereo and SAP (separate audio program) features.
Multipoint
convergence Projection TVs with 3 CRTs require
periodic adjustment to keep the 3 images perfectly aligned. Typically this is a simple 5 minute
procedure the consumer must do every month or so.
Multi-path
interference Some neighborhoods
are plagued with this problem: The
signal finds more than one path to the antenna. Multi-path results from diffraction
around the sides of hills and buildings.
For NTSC sets this will result in ghosts: multiple images shifted
laterally. For DTVs the result can
be an unusable signal, even though it may be strong. The solutions are moving the antenna or
selecting a very directional antenna.
Newer generations of DTV receivers are better able to cope with
multi-path.
Must-Carry This refers to the legal
obligation of cable companies to carry analog or digital signals of
over-the-air local broadcasters.
Native
format Most DTVs will convert the 18 ATSC
formats into 1 or 2 formats and will draw only those. For these sets, the ‘native’
format is 1. a format the set will draw or 2. the original format. (These are contradictory definitions,
but they reflect current practice.
1 is probably the preferred meaning.)
NTSC (National
Television System Committee technical standard) This is analog TV invented in 1946. NTSC has 525 lines (483 visible)
interlaced, 60 fields per second.
This standard is in use in North America, Japan, South Korea, Burma,
Taiwan, the Philippines, and half of South America.
OAR (original aspect
ratio) Also called Letterbox
format, OAR means that none of the image is clipped or squeezed. Unused parts of the screen are usually
black.
OLED (Organic LED) A new display technology. Somewhat resembling plasma, it uses
organic Light Emitting Diodes.
OTA (over the air) There are about 1800 OTA (terrestrial)
TV stations in the U.S.
Over-scan/Under-scan Computer CRT monitors under-scan, which
means they leave a thin black border around the image. TVs over-scan, which means a small part
of the image perimeter is lost.
(Digital displays don’t necessarily do either.)
PAL (Phase Altering
Line standard) This alternative to
NTSC has 625 lines, interlaced, 50 fields per second. It is used in most of
Europe, Asia (except USSR), Africa, and Australia, and half of South America.
Pan-and-scan A method of
broadcasting a wide screen film on a 4:3 channel. Most of the time just the center of the
image is shown. (The right and left
edges are clipped off.)
PCM (Pulse Code Modulation) or L-PCM (Linear
PCM) This 2-channel digital
audio standard is simpler than Dolby Digital.
Pixilation What you see when you sit too close. (You see individual pixels.)
Progressive scan This is the opposite
of interlaced scan.
PSIP
data (Program and System Information
Protocol) This data is arranged as
a table with multiple sub-tables.
The data identifies the station name, what the sub-channels are, the
program name, the following programs, content advisories, language options, and
caption options. Some of this data
is transmitted as often as 7 times per second.
PVP-OPM Protected Video Path Output Protection Management.
Downgrades computer video resolution or blocks the picture entirely if the
connected display doesn't support content protection.
PVP-UAB Protected Video Path User-Accessible Bus. Encrypts video content
as it passes over the PCI Express bus from the high-def disc to prevent other
PCI Express devices from intercepting the video stream.
Rainbow effect A side
effect of delivering the image colors sequentially instead of
simultaneously. DLP displays have
this effect if they use a spinning color wheel or sequentially-firing
LEDs. Most viewers are not bothered
by the rainbow effect.
Raster A group of closely-spaced lines whose
brightness changes so as to appear to be an image.
RGB 1. red-green-blue 2. a 3-wire standard (See component video)
3. a 5-wire standard
(See VGA.)
RGBHV See VGA.
Screendoor
effect If each pixel has a dark
border around it, viewers who sit too close can see it. The effect is somewhat like looking
through a screendoor.
SDTV (standard
definition TV) SDTV is 480i, which
is approximately the resolution of NTSC and DVDs.
SECAM (Sequential Color
And Memory standard) This
alternative to NTSC has 625 lines interlaced, 50 fields per second. It is used in the former USSR, France,
and parts of Eastern Europe, the Middle East, and Africa.
SPDIF (Sony/Philips Digital
Interface) This is digital audio,
and can be either coaxial cable or fiber optic.
STB (Set Top Box) These include satellite receivers, cable
TV receivers, OTA receivers, and various recording devices.
Sub-channels OTA DTV
stations can show multiple programs simultaneously, subject to the 6 MHz
bandwidth limit. This is called multicasting.
SVGA See VGA.
S-video Also called Y/C, this two-wire
standard keeps the color separate from the intensity signal, and thus avoids
the overlapping sideband problem of composite signals. (Converting an NTSC signal to S-video
gains you nothing since what was lost cannot be recreated.) Although the quality of S-video is close
to component video, S-video cannot transport anything better than 480i.
Symbol rate The symbol rate for
ATSC is 10.76 million symbols/sec.
8VSB has 3 bits/symbol.
After the error correction bits are removed the net transfer rate is 19.28 million bits/sec.
THX 1. a standard that theaters try to
meet. 2. equipment to help theaters meet that
standard.
Toslink A fiber optic cable standard.
Transponder A satellite
channel. There is often one program
per transponder. Some transponders
are wider than 6 MHz and can carry more than one NTSC program. Several digital channels can fit on one
transponder.
VGA a 5-wire standard interface,
originally for computer monitors, now common for HDTV monitors. Usually the 5 wires are in one cable. The connector can be either a 15-pin
connector or five BNC connectors.
The signals are usually red, green, blue, horizontal sync, and vertical
sync. But Y, Pr, and Pb can replace
the colors.
Virtual channel number This is the channel
the consumer thinks he is watching.
The actual (physical) channel is selected by a hidden mechanism.
YCrCb Almost identical to
YPrPb. If you connect a YCrCb unit
to a YPrPb unit you might have to adjust the color slightly. YCrCb is an older standard uncommon for
consumer connections.
YPrPb Color representation requires three
independent variables. CRTs prefer
red, green, and blue. Ink jet
printers prefer yellow, magenta, and cyan.
NTSC encodes color as luminance (brightness), hue (color), and
saturation (absence of white in colors).
Storage media such as DVDs prefer Y, Pr, and Pb, where Y is luminance,
Pr is red-Y, and Pb is blue-Y. This
is because Pr and Pb can be at lower resolution and not degrade the image
noticeably, thus saving storage space.
YPrPbHV See VGA.
3:2 pull-down This is the process of converting a 24
frames/sec image into a 30 frames/sec image. Some line-doublers will reverse this
process to acquire the original, and then re-perform it.
4DTV This is a DTV subscription service for
C-band and Ku-band (a satellite service requiring an 8 foot dish).
5.1 channel This is 6 channel
audio. The 6th channel
(the sub-woofer) has reduced bandwidth.
5C Copy Protection
See DTCP.
8VSB modulation technique (8-level vestigial sideband) DTV stations in the U.S. use 8VSB
modulation. This is an AM mode
wherein the carrier is multiplied by an 8-level digital signal, and then a
filter is used to remove all but the carrier and 6 MHz of the upper
sideband. (“8VSB” is
often used as a synonym for OTA.)
The author has B.S. and M.S.
degrees in Electrical Engineering from Carnegie-Mellon University. KQ6QV home page.
This document is Copyright
2002-2009 by Ken Nist. The “document” includes all web pages
at www.hdtvprimer.com. The author
places no restrictions on the use of this document. It may be used by
anyone in any manner for any purpose.