2/8/08
An
HDTV Primer
What you
need to know to buy your first HDTV.
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.
Presently, buying a TV is more
complicated than buying a house. If you try to ‘simplify’
your choice by selecting a standard TV, it will become obsolete before it wears
out.
There are many HDTV primers on
the Internet. Virtually all of them
are written by people with a stake in keeping it simple. The goal of this primer is to actually
make it simpler by exposing all of the hidden problems you will otherwise
discover the hard way.
To learn what you need to know
about HDTV, read through all of the following issues:
Issues:
The Telecommunications
Act of 1996
How is viewing HDTV
different?
What types of sets
are available?
What HDTV
programming is available?
Help! My TV is so
complicated, my wife can't operate it !!!
Primers by other authors: (alternative
reading)
Samsung
Digital TV Guide This
attractive website is an excellent introduction to HDTV.
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 System 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” 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 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 usually only noticeable in
bright whites.
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, Voom, The Outdoor Channel, and Movie Central. 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 are the principal frequencies used
by DirecTV and Dish Network, although DirecTV will probably some day move entirely
to Ka band. (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.