years ago it didn't matter too much
that there were a dozen or so
incompatible systems of television in the world. Distance was a great
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.
Now, incompatible broadcast standards, not to mention scores of different languages, represent a barrier to world-wide 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 ban outside films and broadcasts, and spend millions of dollars each year to try 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.
Plus, 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.
Incompatible Broadcast Standards
A TV 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 incompatibilities in equipment and in the approach to broadcasting the audio and video signals.
Some 14 different SDTV (standard definition) broadcast TV standards have been used at different times throughout the world. They can be reduced to three primary groups:
Within these there are two 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 left us with the 525 and 625 standards for SDTV.
might think all this a bit technical, but hang in there. It's relevant to what you
need to know -- especially with the international exchange of programming being
a growing factor in the field's economic viability. The quick matching
game at the end of the chapter will tell how much of the chapter has
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. When the HDTV standard was introduced it also made use of this wider (generally, 16:9) aspect ratio.
In the picture here, the wider area (just inside the blue borders) represents the 16:9 ratio used in HDTV. Compared to the 4:3 ratio, this aspect ratio conforms to the wider perspective of normal human vision.
The NTSC Broadcast Standard
Before we take up the new ATSC (Advanced Television Systems Committee) digital broadcast standard, we'll take a quick look back at the systems that proceeded it and that are still used in countries that have not made the transition to digital TV.
For almost 50 years he United States used the NTSC (National Television System Committee's) 525-line, 30 frames-per-second system. It was developed in 1941 as the broadcast standard for black and white (monochrome) television.
By 1953, a NTSC 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.
Since the basic NTSC standard was more than 50 years
old, many technical improvements had become possible during the subsequent half-century. Digital TV standards, which we'll cover later
in this module, take advantage of many new technical capabilities and
provide major improvements over the original NTSC standard.
The PAL and SECAM Television Systems
Prior to the introduction of digital broadcasting, more than half of all countries used one of two 625-line, 25-frame systems: SECAM (Sequential Color and Memory) or PAL (Phase Alternating Line).
The extra 100 lines in SECAM and most PAL systems added significant detail and clarity to the video picture, but the 50 fields per second (compared to 60 fields in the NTSC system) meant that the viewer could 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.)
With the 30 frames per-second NTSC video standard converting film to video is more difficult. The ▲ to 30 frames per second frame rate had to be converted to 24 and vise-verse. This took 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.
In the next module we'll take up the new DTV broadcast standards.
(Click on "more" for the second half of this module.)
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