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Optional Audio Introduction
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World Television Standards and DTV/HDTV
Fifty years ago it didn't matter too much that there were a few hundred languages in the world and a dozen or so incompatible systems of television. 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 with a computer and a telephone line. Now, incompatible standards and incomprehensible languages represent a barrier to communication and understanding. Dictators like it that way, and so do people who fear their
views and control will be undermined by a free flow of information. This is why
millions of dollars are being spent by many countries each year to keep out
"undesirable" information. (Just one example, and an example that few people in
the United States know about, is the jamming that has taken place on international
short wave. This is Most of the rest of us — especially those of us that live in democracies—feel that a free flow of information is essential, not only to progress, but to breaking down barriers of misunderstanding between peoples.
This is especially important when you consider that international distribution is essential to financial success. (Films and TV programs represent one of the major exports of the United States. Many U.S. films and TV programs 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 also confront the incompatibilities
between broadcast standards. |
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Although the total number has diminished somewhat, there are still several incompatible broadcast television standards (technical approaches to broadcasting the picture and sound) in the world. This means that a program produced in one country can't be automatically viewed in another country without converting it to the appropriate technical standard. There have been about 14 different broadcast standards in use at different times throughout the world. Today, excluding DTV (digital TV) three basic systems serve the vast majority of countries (although there are some significant incompatibilities within these).
The difference between these basic international broadcast standards centers primarily on four things:
Historically, the number of lines used in standard broadcast TV has ranged from the United Kingdom's 405-line monochrome system to the 819-line system used in France. Both of these systems have now been phased out, leaving us with the 525 and 625 standards for standard definition TV (SDTV).
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Aspect Ratios Although the number of scanning lines
may have varied, until recently all television systems The 4:3 ratio was consistent with motion pictures that predated the wide screen aspect ratios used in CinemaScope, Vista-Vision, and Panavision films. As we will see, HDTV uses a 16:9 aspect ratio. In the picture on the right the inner red box represents standard definition TV (SDTV) and the wider area represents high-definition TV (HDTV). The most commonly used wide-screen movie format is slightly
larger than 16:9 (although the difference is insignificant). However, the
CinemaScope film aspect ratio is considerably wider than 16:9. The National Television Systems Committee's (NTSC) 525 line, 30 frames per second system is shared primarily by the United States, Canada, Greenland, Mexico, Cuba, Panama, Japan, the Philippines, Puerto Rico and most of South America. The NTSC standard was first developed for black and white (monochrome)
television in 1941. In 1953, the color standard was established. The NTSC system of television is referred to as a 525 line, 60-field system because, as we've seen, the 30 frames consist of 60-fields. The NTSC's 60-field system originally based its timing cycle on the 60 Hz (cycle) electrical system used in these countries. Since other countries in the world use a 50 Hz electrical system, it was logical for them to develop 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 that half-century. Digital TV (DTV) standards, which we'll elaborate on later, take advantage of many new technical capabilities and provide major improvements over the original NTSC standard.
More than half of the countries in the world use one of two 625 line, 25 frame systems: the SECAM (Sequential Color and Memory) or the PAL (Phase Alternating Line) system. SECAM was originally developed in France as a non-compatible system designed to protect the country's manufacturing industry from foreign electronic imports. Because SECAM is incompatible with other TV systems, it was adopted by the Communist countries in part to prevent their people from seeing and being influenced by TV programming from noncommunist countries. Technically, SECAM is the simplest TV system in the world. 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 of the PAL systems have 625 lines. The extra 100 lines in the SECAM and most of the 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 that a slight flicker can sometimes be noticed. Even so, the 25 frames per second (fps) standard is very close to the international film standard of 24 fps. Therefore, the 24 fps film standard is easily converted to the PAL and SECAM video systems. (Slightly speeding up film to 25 fps is hard to notice.)
With NTSC television, converting
film to video is more difficult; the 24 frame-per-second film rate must be converted
to 30 frames-per-second. This takes a bit of "fancy footwork,"
HDTV contains over two-million individual picture elements that result in pictures that are six to ten times sharper than regular television images (SDTV). The greater sharpness of HDTV is coupled with the wide-screen (16:9) images and Dolby Digital 5.1 Surround-Sound. The difference in clarity between the SDTV and HDTV systems will be illustrated in part two of this module, and surround-sound and 5.1 audio will be explained in Module 42. The table below compares the basic attributes of the SDTV and HDTV television systems. Note that although HDTV is considered to have 1,125 lines, only 1,080 of these are considered "active" or visible on the screen.
According to the original timetable established in 1997 by the FCC, by the year 2006, all SDTV TV stations in the U.S. were to be phased out in favor of DTV (digital television) stations. Even through the FCC deadline for the transition has now been effectively moved to 2009, there is still some doubt whether TV stations will be willing to shut down all their current analog channels and allow them to be reassigned to other services. Despite attempts to educate the public, there is concern that a significant number of home viewers will not understand the change and take the steps necessary to be "digital ready." Having their favorite TV stations suddenly and permanently go black would obviously have serious political implications. All 1,240+ commercial TV stations in the United States have been assigned new digital frequencies by the FCC (Federal Communications Commission), the primary governing agency for broadcasting. These are all higher frequencies than the analog transmissions—channels 2-13 being the most commonly used. This means that despite the greater effectiveness of digital
signals, in many cases more transmitter power will be needed to reach the same coverage
area. Almost all U.S. TV stations have initiated some level of digital service—even though in some cases that involves a low-power transmitter with a limited range. The graph on the right shows the rate of growth for digital TV stations since 1998. 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. For sets with smaller screens, the digital requirements are to be phased in over the subsequent years. This is a controversial mandate and it is being challenged by set manufacturers. For cable subscribers a special digital tuner will not be necessary—assuming the cable systems relay the digital transmissions. Many cable systems have been reluctant to make the necessary investment in digital equipment. However, competition from digital satellite services seems to be accelerating cable's move to digital.
Unlike SDTV, which has only one broadcast standard in the United States, there are 18 digital options within the new U.S. DTV/HDTV standards. Although it might seem that having all of these different approaches would represent chaos, it's expected that TV tuners will be able to automatically sort them out and deliver a picture to whatever TV set you are using. The standards vary in the following three ways.
(Click on "more" for the second half of this module.) |
had
a 4:3 aspect ratio. The aspect ratio is the width-height
proportion of the picture.
(Note
the January, 1954 issue of Popular Mechanics on the left that heralded the
arrival of color TV.)
