Some Americans may have sent video home movies to a European relative, only to discover that the images are scrambled and the sound quality is very poor. This is caused by a major difference in broadcast formats used by the United States and many other countries. The United States favors a format called NTSC, which is short for National Television Standards Committee, while Europe, Australia and parts of Asia use a competing format called PAL, or Phase Alternating Line.
Most of us would not be able to recognize the difference between NTSC and PAL, but then again most of us aren't television broadcast engineers. The differences really start with the electrical power system behind the transmissions. In the United States and other countries, electrical power is generated at 60 hertz, so for technical reasons the NTSC signal is also sent out at 60 'fields' per second. Since most televisions use an interlaced system, this means that 30 lines of the image are sent out, followed by the alternating 30 lines. This line alternation happens so fast that it becomes undetectable, much like a film running through a projector. The result for an NTSC television is 30 frames of a complete image appearing every second.
Since Europe uses a 50 hertz power supply, the equivalent PAL lines go out at 50 fields per second, or 25 alternating lines. PAL televisions only produce 25 complete frames per second, which can cause some problems with the proper display of motion. Think of it as the 'silent movie effect', in which the actors seem to move a little faster because there are fewer frames showing movement. If a PAL movie is converted to an NTSC tape, 5 extra frames must be added per second or the action might seem jerky. The opposite is true for an NTSC movie converted to PAL. Five frames must be removed per second or the action may seem unnaturally slow.
Another difference between NTSC and PAL formats is resolution quality. PAL may have fewer frames per second, but it also has more lines than NTSC. PAL television broadcasts contain 625 lines of resolution, compared to NTSC's 525. More lines usually means more visual information, which equals better picture quality and resolution. Whenever an NTSC videotape is converted to PAL, black bars are often used to compensate for the smaller screen aspect, much like letterboxing for widescreen movies.
When the NTSC format was first adopted in 1941, there was little discussion of color transmissions. When the technology for color television arrived, engineers had to create a broadcast method which would still allow owners of monochrome television sets to receive a picture. Color signals on the NTSC format are still not considered ideal by electronics experts. The PAL system, on the other hand, was created after the advent of color broadcasting, so color signals are much truer to the original image.
For most purposes, the difference between NTSC and PAL signals are negligible. A European television set won't work in the United States and an NTSC formatted
DVD won't play on a PAL player. But many people own home movies which cannot be viewed on a competing format. For this reason, there are a number of companies which offer conversion kits from NTSC to PAL or PAL to NTSC. Some of these conversion methods can be time-consuming and variable in quality, but others provide an easy way to create a PAL video for a European relative or an NTSC DVD for a Canadian friend. Some electronic media outlets may also provide conversion services for a price.
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A4 and the other A paper sizes are based on metric measurements. An A0 piece of paper, when spread flat, equals one square meter. A0 paper, folded in half, is a size A1. A1 folded in half is A2, and so on through A6. This produces paper with different sizes, but all with a 1.414:1 height-width ratio. European standards also cover B paper; B0 paper is a meter wide and 1.414 meters tall; B1 is B0 folded in half, and so forth through B5.
