Why are we converting to Digital TV?

In answer to that question, one of the early developers of DTV said "It's really a saga." The conversion we are in the midst of was a germ of an idea in 1986, when Broadcasters were attempting to fight off an attempt by Land Mobile lobbyists to convince the FCC that they needed excess UHF spectrum. After all, broadcasters weren't doing anything with many vacant UHF channels. Why not use the spectrum for police, ambulance, delivery services and other two-way radio needs? According to a remarkable book by Joel Brinkley called Defining Vision, it was this challenge to broadcasters spectrum that led to the concept of a U.S. version of high definition television that would require all that UHF spectrum to be successful.

The greatest challenge was fitting a high definition signal onto one channel. Scientists found this was possible if they digitized the signal and compressed it by taking out any redundant bits. This led to a concept that exceeded the expectations of high definition crystal clear pictures. Now, you could use these compression techniques to squeeze multiple standard definition signals into one digital channel and perhaps carry more than just video down that pipeline. Why not allow access to the Internet or what about telephone capabilities through your television?

What is the timetable?

The largest network-affiliated stations in the top ten markets had a DTV signal on the air by May, 1999. Stations in the top 30 markets must be on the air by November 2000. By 2002, all commercial stations will have to have DTV programming on the air. Public Television stations have an additional year, until 2003, to make the conversion. All stations have been assigned an extra channel, most in the UHF spectrum, to enable them to begin digital television operations while keeping their current analog signals on the air. While the current rules mandate the shut down of all analog signals by 2006, it's unlikely this will occur until years later.

Alabama Public Television expects to have digital transmissions in some portions of the state available as early as fall 2000.

Can my existing TV pickup these DTV programs?

No. The digital television standard is 100% not compatible with current televisions. Fortunately, converter boxes are now becoming available to allow existing analog sets to pick up DTV programming. However, most of the new features of DTV such as wide screen pictures, high definition programming, and enhanced DTV will only be available through true HDTV sets.

Why is DTV a different screen size?

This is actually one of the key attractive features that might lead you to purchase a new DTV set and one of the most exciting production matters as well. Our present screen has a boxy 3x4 aspect ratio, but DTV sets will be widescreen 16x9 aspect ratio, much like what you see at the movie theatre. Producers are beginning to shoot videotape in widescreen to future proof this material for digital televisions. That is why you are beginning to see more programs using what's called a "letterbox" screen. They are distributing to your TV the full widescreen pictures within our normal box-like television sets and blacking out the top and bottom. Of course, motion pictures shot on 35mm film have been widescreen for decades, so they convert naturally to 16x9. Televised sports will also attract attention using this new widescreen ratio, because you will see much more of the action. Some of the early developers felt the widescreen approach was even more important than high definition.

How big a TV set do I need to buy and why does it have to be bigger?

The advertised size of a television sets in the U.S. is the size of the viewable picture, measured diagonally. These diagonal measurements can be misleading when comparing conventional and DTV sets. Here's a scale drawing comparing a 25" standard set -- a popular size -- with a theoretical 25" DTV screen:

Analog 3x4 Set vs. Digital 16x9 Set

A wide-screen DTV set will look quite a bit smaller than an NTSC set of the same advertised size. One way to compare NTSC and DTV sets more fairly is to compare the diagonal measurement of the NTSC screen with the width of the DTV screen. Continuing the example, a 28" or 29" (advertised) DTV set will appear approximately as large as a 25" NTSC set:

The lesson? Bring a tape measure to the store when shopping for an DTV set. Be sure to check how deep the set is also;first-generation DTVs will have very long picture tubes. You'll also need a strong friend or two to help lug the thing home. The new sets will be HEAVY until they perfect the flat plasma displays.

What programs will be in High Definition?

Since the majority of national television programs are recorded on film, it is relatively easy to convert them to HDTV.
And more programming is also being produced directly to HDTV videotape including many PBS documentaries, ABC Monday Night Football, The Tonight Show on NBC, etc.

Quick Definitions:

What is Digital Television?

The picture you now receive is based on an analog transmission system that is 50 years old. In 1996, the FCC approved the U.S. standard for digital television. In a digital system, images and sound are captured using the same digital code found in computers -- ones and zeros. With DTV you will also either get a great signal or none at all.

What is High Definition Television?

HDTV is a form of digital television. DTV will allow stations to broadcast programs either at HDTV resolution or with standard resolution. With HDTV resolution, images will be double the lines of resolution of today's television and provide six-channel CD-quality surround sound Dolby audio.

What is multicasting?

Some PBS broadcasters plan to transmit as many as six channels of standard definition programming simultaneously over they digital signal. This is called multicasting. Standard definition pictures aren't up to the quality of HDTV, but are an improvement over our present picture.

What is datacasting or enhanced TV?

Because DTV is digital, other images, transcripts, teacher's guides, audio, etc. can be delivered to your DTV set while you are watching a program. You might be able to access the Internet and send email over DTV as well. Enhanced TV is a model which would allow you to receive in-depth information about aspects of a program via web-like pages of information and images while the program is being watched.

How does DTV offer so much information?

The key is compression. Compression allows a vast amount of data to be reduced for transmission. In the U.S., the DTV signal is reduced to 19.4 million bits per second. As a comparision, your phone line at home handles 28,000 bits per second

For more in-depth information about Digital Television, check out our favorite DTV LINKS.

For more information:   info@cpt.ua.edu