SBE 24 DTV Handout


Presented by the
Society of Broadcast Engineers
Chapter 24
Your local Broadcasters


The Federal Communications Commission has requested and Congress has passed into law, a new form of television broadcasting called Digital Television. DTV will replace our current analog system of broadcasting that we have enjoyed since 1954. All television stations must convert to the new system by 2003. The current system of analog TV will be broadcast simultaneously with the newer Digital system until 85% of the viewing public has acquired the new Digital TV sets.

Why migrate to Digital Television

Audio and video signals have been slowly moving from the analog domain to the digital domain. Today the audio CD, a digital format, has largely replaced the vinyl LP record, an analog format.

There are three principle reasons for the migration to digital. They encompass the areas of quality, efficiency and enhanced services.

All analog recording and playback systems suffer from the effects of noise and distortion, unless extraordinary care is taken during each step of the recording, distribution and reproduction process. The slight quality loss that occurs when analog signals are converted to digital is insignificant when compared to the degradation that an analog signal suffers as it travels through the distribution chain. All digital copies of digital source material are identical. In the analog domain, each copy of a copy suffers the indignities of added noise and distortion. For the first time, the home viewer can enjoy the same level of quality that the broadcaster has in the studio.

The second reason for moving toward digital is the increase in spectrum efficiency that results from the use of data compression techniques. Just as we can "zip" a large data file to reduce the size of the file to conserve disk space, we can also compress audio and video files. DTV uses a more aggressive compression called lossy compression. The trick is to use a compression algorithm that will have the highest compression ratio while having the least amount of visible picture degradation. In HDTV, a 1.5 Gigabit/second data stream is compressed (or "zipped" if you prefer) to a data stream of only 19.4 Megabit/second! This allows us to send higher quality video and audio in the current 6 MHz broadcast channel.

The third advantage that digital offers over the present analog system is in the area of additional services and information that can be delivered to the viewer. The NTSC system has the ability to send some additional data along with the program video and audio. This additional data consists of closed captioning, test signals and a secondary audio program (SAP). Digital TV will have greater data capacity, allowing the broadcaster to send web pages, electronic program guides and multimedia enhancements to primetime programming. DTV will support multiple audio streams and multilingual closed captioning. DTV will offer a superior audio and visual experience, with many additional enhancements not possible with our current analog system.

What is HDTV

HDTV (High Definition TV) is a subset of the DTV (Digital TV) specification defined by the ATSC. HDTV is generally accepted to mean any DTV system with 720 lines of resolution or more and having a 16:9 aspect ratio.

Is Digital the same as DTV

Digital is a generic term for any digital signal. There are many systems that use digital signals. Examples are modems, FAX machines, Audio CDs, DVDs, Digital cable and DTV. Not all devices that use digital signals are compatible, for example a FAX machine will not understand the digital data stream produced by an audio CD. DTV is a specific type of digital data, whose parameters have been defined by the Advanced Television Systems Committee (ATSC).

What is the basic difference between DTV and regular TV

Digital encodes video and audio information using the same techniques as the DVD. It eliminates the problems that plague regular analog broadcasting, such as, ghosts and echoes, ignition noise and snowy pictures. DTV also eliminates the technical problems of "cross-color" and "cross-luminance" artifacts. The digital format also allows the broadcaster to pack more information into the DTV signal. A signal DTV channel can carry several virtual channels, identified as N-1 and N-2, where N is the assigned major channel number. DTV also allows the broadcast of higher quality High-Definition (HDTV) pictures, which preserves image quality when displayed on big screen monitors (those larger that 40 in). The advantages of DTV apply to small screens as well as large screens. HDTV programs are most impressive on large screens. Most of the DTV/HDTV sets currently on the market are of the large screen format. As the market matures, we will see more sets available in the 25-in. to 36-in. size.

What do I need to receive DTV

DTV can only be received with a DTV television or a DTV converter box. Converter boxes are available for less than $600 and allow the reception of regular TV broadcasts, the new DTV broadcasts, satellite signals and regular analog cable TV signals using the same set-top box.

Can I receive DTV using cable TV

The cable television industry has taken a "wait and see" attitude toward DTV. The cable industry has released a proprietary version of Digital Cable that is incompatible with terrestrial DTV, requiring a separate converter box. Until your cable operator carries DTV, you will need an antenna for over the air reception. There has been some success using indoor antennas, but best results are obtained with outdoor antennas. The are new, less obtrusive, antenna styles available. Consult your DTV sales and service specialist for more information on antennas.

Can I receive DTV broadcasts on my NTSC TV* set

Yes- providing you use a DTV converter box. Wide screen DTV signals will be shown in "letter box" format. Converter boxes can attach to your existing set by either an antenna connection or by using separate audio and video cables.

*(NTSC- National Television Systems Committee- formalized the system of television that we have enjoyed since its adoption by the FCC in 1953.)

Why do some DTV sets have a wider screen width

One of the improvements that DTV provides is a wider screen format called 16:9. This "wide screen" format allows you to see picture information that is other wise cut off in the standard 4:3 picture format that we are used to. Various techniques are used to display widescreen video on a 4:3 display and 4:3 video on the "widescreen" displays. Your DTV dealer can demonstrate the display options available on various DTV receivers.

Can you channel surf when you have a DTV set

Sure, but there’s an easier way. Part of the DTV standard is a built in program guide that each DTV television station will send to the DTV receiver. You only need to scan the program guide, which lists the program names and some additional info such as plot or story line. Select the program you want to watch with a click of your remote control and the TV will tune itself to that program.

Who is transmitting DTV in the Madison market?

At the current time the following services are available on DTV


FOX and PBS are expected to join the DTV lineup as soon as their transmission facilities are completed.

For additional information of the history of television and the development of Digital Television read

Tube- The Invention of Television

By David E. Fisher and Marshall Jon Fisher
A Harvest Book/ Harcourt Brace and Company

Defining Vision- How broadcasters Lured the Government Into Inciting a Revolution in Television

By Joel Brinkley
A Harvest Book/ Harcourt Brace and Company

If you would like more information about Digital Television, log on to these web sites
Federal Communications Commission- rules and regulations
Consumer Electronics Association marketing and public relations web site, has links to other related sites
the standard setting organization for DTV/HDTV
wealth of information on DTV/HDTV
Society of Broadcast Engineers- Madison Chapter 24
Society of Motion Picture and Television Engineers
originator of the audio technology used in DTV
consumer oriented site, has a glossary and links to equipment manufacturer sites

ã 2001 by SBE Chapter 24. Compiled by Steve Paugh, CBTE, with the cooperation of Chapter 24 of the Society of Broadcast Engineers. Views expressed herein do not necessarily reflect the official positions of the Society, its officers, or its members. SBE Chapter 24 regrets, but is not liable for, any omissions or errors

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