What is a HDTV?

When the first high-definition television (HDTV) sets hitcan't decode and display digital signals. When analog
the market in 1998, movie buffs, sports fans and techbroadcasting ends, you'll only be able to watch TV on
aficionados got pretty excited, and for good reason.your trusty old set if you have cable or satellite service
Ads for the sets hinted at a television paradise withtransmitting analog signals or if you have a set-top
superior resolution and digital surround sound. Withdigital converter.
HDTV, you could also play movies in their originalThis brings us to the first big misconception about
widescreen format without the letterbox "black bars"HDTV. Some people believe that the United States is
that some people find annoying.switching to HDTV, that all they'll need for HDTV is a
But for a lot of people, HDTV hasn't delivered anew TV and that they'll automatically have HDTV
ready-made source for transcendent experiences inwhen analog service ends. Unfortunately, none of this
front of the tube. Instead, people have gone shoppingis true.
for a TV and found themselves surrounded byHDTV is just one part of the DTV transition. We'll look
confusing abbreviations and too many choices. Someat HDTV in more detail, including what makes it
have even hooked up their new HDTV sets only todifferent from DTV, in the next section.
discover that the picture doesn't look good.The ATSC has created 18 commonly used digital
Fortunately, a few basic facts easily dispel all of thisbroadcast formats for video. The lowest quality digital
confusion. In this article, we'll explain the acronyms andformat is about the same as the highest quality an
resolution levels and give you the facts on the Unitedanalog TV can display. The 18 formats cover
States transition to all-digital television. We'll also tell youdifferences in:
exactly what you need to know if you're thinking aboutAspect ratio - Standard television has a 4:3 aspect
upgrading to HDTV.ratio - it is four units wide by three units high. HDTV
Analog, Digital and HDhas a 16:9 aspect ratio, more like a movie screen.
For years, watching TV has involved analog signalsResolution - The lowest standard resolution (SDTV)
and cathode ray tube (CRT) sets. The signal is madewill be about the same as analog TV and will go up to
of continually varying radio waves that the TV704 x 480 pixels. The highest HDTV resolution is 1920
translates into a picture and sound. An analog signalx 1080 pixels. HDTV can display about ten times as
can reach a person's TV over the air, through a cablemany pixels as an analog TV set.
or via satellite. Digital signals, like the ones from DVDFrame rate - A set's frame rate describes how many
players, are converted to analog when played ontimes it creates a complete picture on the screen
traditional TVs. (You can read about how the TVevery second. DTV frame rates usually end in "i" or "p"
interprets the signal in How Television Works.)to denote whether they are interlaced or progressive.
This system has worked pretty well for a long time,DTV frame rates range from 24p (24 frames per
but it has some limitations:second, progressive) to 60p (60 frames per second,
Conventional CRT sets display around 480 visible linesprogressive).
of pixels. Broadcasters have been sending signals thatMany of these standards have exactly the same
work well with this resolution for years, and they can'taspect ratio and resolution - their frame rates
fit enough resolution to fill a huge television into thedifferentiate them from one another. When you hear
analog signal.someone mention a "1080i" HDTV set, they're talking
Analog pictures are interlaced - a CRT's electron gunabout one that has a native resolution of 1920 x 1080
paints only half the lines for each pass down thepixels and can display 60 frames per second,
screen. On some TVs, interlacing makes the pictureinterlaced.
flicker.Broadcasters get to decide which of these formats
Converting video to analog format lowers its quality.they will use and whether they will broadcast in high
United States broadcasting is currently changing todefinition - many are already using digital and
digital television (DTV). A digital signal transmits thehigh-definition signals. Electronics manufacturers get to
information for video and sound as ones and zerosdecide which aspect ratios and resolutions their TVs
instead of as a wave. For over-the-air broadcasting,will use. Consumers get to decide which resolutions
DTV will generally use the UHF portion of the radioare most important to them and buy their new
spectrum with a 6 MHz bandwidth, just like analog TVequipment based on that.
signals do.Until the analog shutoff date, broadcasters will have
DTV has several advantages:two available channels to send their signal - a channel
The picture, even when displayed on a small TV, isfor analog, and a "virtual" channel for digital. Right now,
better quality.people can watch an over-the-air digital signal only if
A digital signal can support a higher resolution, so thethey are tuned in to the broadcaster's virtual digital
picture will still look good when shown on a larger TVchannel. After analog broadcasting ends, the only
screen.signals people will receive over the air will be digital.
The video can be progressive rather than interlaced -However, even though a digital signal is better quality
the screen shows the entire picture for every framethan an analog signal, it isn't necessarily high definition.
instead of every other line of pixels.HDTV is simply the highest of all the DTV standards.
TV stations can broadcast several signals using theBut whether you see a high-definition picture and hear
same bandwidth. This is called multicasting.the accompanying Dolby
If broadcasters choose to, they can include interactiveDigital® sound depends
content or additional information with the DTV signal.on two things. First, the station has to be broadcasting
It can support high-definition (HDTV) broadcasts.a high-definition signal. Second, you have to have the
DTV also has one really big disadvantage: Analog TVsright equipment to receive and view it.