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CCIR System M,[1][2][3] sometimes called525–line,NTSC,NTSC-M, orCCIR-M,[4][5] is the analogbroadcast television system approved by theFCC (upon recommendation by the National Television System Committee - NTSC)[6] for use in theUnited States since July 1, 1941,[7][8] replacing the441-line TV system introduced in 1938.[8] It is also known asEIA standard 170.[9] System M comprises a total of 525 interlaced lines of video, of which 486 contain the image information, at 30 frames per second. Video is amplitude modulated and audio is frequency modulated, with a total bandwidth of 6 MHz for each channel, including a guard band.[10]
It was also adopted in theAmericas andCaribbean;Myanmar,Philippines,South Korea,Taiwan,Thailand, andJapan (here with minor differences, informally referred to asSystem J). System M doesn't specify a color system, butNTSC color encoding was normally used, with some exceptions:NTSC-J in Japan,PAL-M inBrazil andSECAM-M inCambodia,Laos, andVietnam (seeColor standards section below).
The letter M designation was attributed by theITU at the 1961 Stockholm meeting (seeITU identification scheme).[11]
In 1965, Thailand decided to replace System M with the 625-lineCCIR System B, which began implementation in 1967 and eventually adopted the PAL color standard.[12]
Circa 2003, the transition from analog System M todigital television broadcasting began, and in 2009 the United States ended high power analog transmissions. Other nations such as Japan, South Korea, and Taiwan also transitioned to digital while the Philippines remain on analog transmissions with digital simulcasts.
Some of the important specifications for System M are listed below:[13]
Strictly speaking, System M does not designate how color is transmitted. However, in nearly every System M country, NTSC color encoding is used forcolor television. This combination is called NTSC-M, but usually simply referred to as "NTSC", because of the relative lack of importance of black-and-white television. In NTSC-M and Japan's NTSC-J, the frame rate is offset slightly, becoming30⁄1.001 frames per second, usually labeled as the rounded number 29.97.
The main exception to System M's being paired with NTSC color is Brazil, wherePAL color is used instead, resulting in the PAL-M combination unique to that country. It is monochrome-compatible with other System M countries, but not compatible with other PAL countries, which use625-line based systems.
Between 1970 and 1991 a variation of the SECAM color system, known as SECAM-M, was used in Cambodia,[14] Laos, and Vietnam (Hanoi and other northern cities).
Clear-Vision is a Japanese EDTV (Extended Definition TV)[15][16] television system introduced in the 1990s, that improves audio and video quality while remaining compatible with the existing System M broadcast standard.[15][17] Developed to improveanalog NTSC,[18] it adds features likeprogressive scan,ghost cancellation andwidescreen image format.[19]