Optional Audio Introduction

Updated: 05/11/2008

Module 9-A

Part I

World Television

Standards and

DTV/HDTV

Fifty years ago it didn't matter much that there were a dozen or so incompatible systems of television in the world. Distance was a great insulator.

But times have changed.

Today, satellites link every country with television, and the Internet provides video, audio, and the written word to virtually anyone anywhere who has a computer and telephone line.

Now, incompatible broadcast standards, not to mention scores of different languages, represent a barrier to communication and understanding.

Dictators like it that way, as do others who fear that the free flow of information will undermine their views and threaten their control.

This is why many countries spend millions of dollars each year to keep out undesirable information. (An example that few people in the United States know about is the jamming that has taken place on international short wave. This is discussed here.)  Recall that we previously discussed the meaning of the colored boxes before these links.

Most of the rest of us -- especially those who live in democracies -- feel a free flow of information is essential not only to progress, but also to dissolve barriers of misunderstanding between peoples.

Films, TV, and the Internet -- and especially e-mail between individuals in different countries -- all show that, despite conflicting politics and religions, people the world over have pretty much the same hopes, fears, and dreams. Touching on these basic human similarities is a major goal of TV production.

International program distribution is essential to financial success. Films and TV programs represent two of the major exports of the United States. In fact, many productions don't begin to show a profit until they go into international distribution.

In addition to the problems related to a free flow of ideas and information we must confront technical incompatibilities among broadcast systems.

This means a program produced in one country can't automatically be viewed in many other countries without converting it to a different technical standard. These technical differences relate to both to incompatibilities in equipment and in the approach to broadcasting the audio and video signals.

Some 14 different TV broadcast standards have been used at different times throughout the world. Excluding DTV (digital TV), today the following three basic systems serve the vast majority of countries, although some significant incompatibilities exist within some of them:

Within these there are four major differences:

Historically, the number of lines used in standard broadcast TV has ranged from the United Kingdom's 405-line system to France's 819-line system. The phase-out of both these systems has left us with the 525 and 625 standards for SDTV (Standard-Definition TV).

You might think this a bit technical, but hang in there. It's relevant to what you need to know.  The quick matching game at the end of the chapter will tell how much of the chapter has sunk in.

Aspect Ratios 

Although the number of scanning lines may have varied, until recently all television systems had a 4:3 aspect ratio. The aspect ratio is the width-height proportion of the picture.

The 4:3 ratio (note red box in the photo on the right) was consistent with motion pictures that predated the wide screen aspect ratios used in CinemaScope, VistaVision, and Panavision.

HDTV uses a 16:9 aspect ratio. In the picture here, the wider area represents HDTV.

The most commonly used wide-screen movie formats are slightly larger than 16:9 (although the difference is insignificant). The CinemaScope film aspect ratio, however, is wider than 16:9.
 

The NTSC Broadcast Standard 

The United States, Canada, Greenland, Mexico, Cuba, Panama, Japan, the Philippines, Puerto Rico, and most of South America share the National Television System Committee's (NTSCs) 525-line, 30 frames-per-second system.

The NTSC standard for black and white (monochrome) television was developed in 1941. By 1953, a color standard had been finalized. (Note the January 1954 issue of Popular Mechanics announcing the arrival of color TV in the United States.)

We refer to the NTSC system of television as a 525-line, 60-field system because, as we saw in Module 8, the 30 frames consist of 60 fields.

The NTSC's 60-field system originally based its timing cycle on the 60 Hz (hertz or cycle) electrical system these countries use.

Since other countries in the world use a 50 Hz electrical system, they developed systems of television based on 50 fields per-second.

The basic NTSC standard is more than 50 years old, and many technical improvements came along during the subsequent half-century. Digital TV standards, which we'll cover later, take advantage of many new technical capabilities and provide major improvements over the original NTSC standard.
 

The PAL and SECAM Television Systems

More than half of all countries use one of two 625-line, 25-frame systems: SECAM (Sequential Color and Memory) or PAL (Phase Alternating Line).

France originally developed SECAM as a non-compatible system designed to protect their country's manufacturing industry from foreign electronic imports.

Because SECAM is incompatible with other TV systems, Communist countries adopted it in part to prevent their people from seeing and being influenced by TV programming from noncommunist countries. Technically, SECAM is the simplest TV system.

PAL is a modified and somewhat improved version of NTSC. It was developed in Germany and is used in Britain and most of Western Europe. Except for Brazil, all PAL systems have 625 lines.

The extra 100 lines in SECAM and most PAL systems add significant detail and clarity to the video picture, but the 50 fields per second  (compared to 60 fields in the NTSC system) means the viewer can sometimes notice a slight flicker.

Even so, the 25 frames-per-second (fps) standard is very close to the international film standard of 24 fps. Therefore, we can easily convert the 24-fps film standard to the PAL and SECAM video systems. (Slightly speeding up film to 25 fps is hard to notice.)
 

The Film and Video Conversion Processes

With NTSC television, converting film to video is more difficult; we must convert the 24 frame-per-second film rate to 30 frames per second.

This takes a bit of fancy footwork, as explained here. This link also explains how we convert NTSC video to PAL and SECAM video and vice versa.
 

Digital and High-Definition Television

HDTV contains over two million individual pixels, resulting in pictures six to ten times sharper than SDTV.

The greater sharpness of HDTV is coupled with the wide-screen (16:9) images and Dolby Digital 5.1 surround-sound.

We'll illustrate the difference in clarity between SDTV and HDTV in Part Two of this module, and we'll explain surround sound and 5.1 audio in Module 42.

The table below compares the basic attributes of U.S. SDTV and HDTV television systems. Note that, although we consider HDTV to have 1,125 lines, only 1,080 of these are "active" or visible on the screen.

According to the original timetable that the FCC (the Federal Communications Commission, the primary governing agency for U.S. broadcasting), by the year 2006 all SDTV television in the U.S. was to be phased out in favor of DTV (digital television). Of course, it didn't happen -- primarily because things couldn't move that fast. 

The FCC has now moved that deadline to Feb. 17, 2009. But as that date approaches, doubt exists about whether all TV stations will be ready to shut down all their current analog channels and reassign them to other services.

Despite attempts to educate the public, by mid-2008, about 35% of people weren't even aware that the change that would take place. Although only stations being received up by rabbit ear or rooftop antennas are affected, that's still a significant percent of the population.

The FCC has assigned new TV channels to all 1,240-plus commercial TV stations in the United States. All are on higher frequencies than the present analog transmissions on channels 2 through 13.

Despite the greater effectiveness of digital signals, because of the higher frequencies involved, transmitters will generally need more power to reach their original (analog) coverage areas.

Almost all U.S. TV stations have now initiated some level of digital service -- even though at this point some only involve low-power transmitters with a limited range.

To expedite the digital conversion process, in August 2002 the FCC voted to require manufacturers to add digital tuners to all TV sets with screens of 36 inches or more. The digital requirements for sets with smaller screens are to be phased in over subsequent years.
 

The Anatomy of Digital TV Signals

Unlike SDTV, which has only one broadcast standard in the United States, eighteen digital standard options exist within the new U.S. DTV/HDTV standards.

Although it might seem these different approaches would represent technical chaos, TV tuners have been designed to automatically sort out the differences and deliver a standard signal to TV receivers.

DTV standards vary in three ways.

(Click on "more" for the second half of this module.)

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