Ed begins:
I just found your Web page on international video standards, and while
it looks very good I did see some passages I wanted to comment on.
"PAL is not the only colour system in widespread use with 50Hz; the French designed a system of their own - primarily for political reasons to protect their domestic manufacturing companies - which is known as SECAM, standing for SEquential Couleur Avec Memoire. The most common facetious acronym is System Essentially Contrary to American Method, SECAM was widely adopted in Eastern Block countries to encourage incompatibility with Western transmissions - again a political motive."
This wasn't as great an issue as it may seem, since most of the Warsaw Pact countries along the old "iron curtain" used systems D and K, which were already incompatible with their Western neighbors' systems. A group at a Russian research institute called NIIR was working on its own improved version of the SECAM system (sometimes referred to as SECAM IV) in the mid- 1960s, so the Soviets agreed with France to jointly work on perfecting the NIIR system; when this effort came to nothing the Soviets, as per the agreement, adopted the present SECAM III system. I'm told that another reason that the Soviets preferred SECAM was that, unlike PAL, it wasn't of German origin.
(There was a strange incident in 1966 when the Soviet government used this agreement as a pretext to cancel the taping of an NBC special in Moscow; the network had sent a complete color outside broadcast unit over to record the show, but the Soviets at the last minute ordered them not to use their NTSC gear claiming that that would somehow violate the SECAM pact with France!)
"The oldest still operational of the stereo sound systems is the American MTS system based on NTSC transmissions, only slightly more recent is the twin channel FM-FM system used in Germany, Austrua, Australia, the Netherlands and Switzerland. The most recent system, NICAM 728, was designed by the BBC in the late 1980s using digital audio technology."
Actually there are four stereo systems in use today. The Japanese system, called EIAJ after the Electronics Industry Association of Japan, was in limited use as early as 1970 during Expo 70 in Osaka; regular service began in 1978. It uses a subcarrier within the main FM audio carrier, but it's an FM subcarrier rather than the suppressed AM subcarrier used in the U.S. system or in FM radio broadcasting.
The German system -- which I'm told is actually called Zweiton -- went into regular service in fall 1981, I believe during the Funkaustellung in August. The U.S. system -- called BTSC, for the Broadcast Television Systems Committee -- was authorized for use in March 1984, though regular service didn't begin on a large scale until July 1985. ("MTS" is a generic term that does not refer to only one system.)
Finally, the BBC was testing NICAM as early as 1983 -- I first heard of it from a Wireless World article in 1984 -- and I believe it went into service in fall 1988, although at that time only from the Crystal Palace BBC1 and BBC2 transmitters.
"The US Closed Captioning mechanism came about through political pressure from the Deaf organisations in the USA and has not been developed beyond the simple job of producing subtitles for the Deaf."
The line-21 system was originally developed by the National Bureau of Standards to transmit exact time of day information from NBS through the U.S. TV networks; NBS later expanded it to provide captioning, and the project was later passed on to the Public Broadcasting Service and finally to the National Captioning Institute.
Line-21 captioning, since it began in regular service in March 1980, has always had a rudimentary text capability that allowed a message to scroll up the screen continuously. More recently, the Electronics Industries Association has issued a standard (EIA-608) that not only has enhanced text capabilities -- such as captions appearing on backgrounds of different colors -- but adds a capability to transmit things like station call letters, network names, program titles and descriptions and weather or other emergency warnings (and, after all these years, the exact time of day!). Incidentally, the official name of the line-21 system is CaptionVision, although this name wasn't adopted until 1993 and not all manufacturers use it.
EIA-608 will probably be extended this year to include information on the intended age level and content advisories (violence, language, nudity, etc.) for each program; the Telecommunications Act of 1996, which went to the President for signature last week, will require TV manufacturers to add a blocking feature to most TV sets (the same ones required to have CaptionVision decoders) at some point after early 1998. Program producers won't be required to add these codes to programs, but distributors will be required to transmit such codes if they are present.
"A few US stations have now adopted the BBC-style Teletext and a few manufacturers, most notably Zenith, fit the decoders to their sets."
Sadly, these are gone now. When the caption decoder requirement went into effect in 1993, Zenith couldn't economically add a CaptionVision decoder to the digital chassis that their teletext TVs used, so they dropped that series and flushed teletext down the drain as far as the U.S. market was concerned. The most commonly available teletext service in this country, Electra, was shut down a year later. ITT Semiconductors has since developed a single chip to decode both WST and CaptionVision, but no one seems interested in it.
"Lower Gamma Ratio - The gamma value for NTSC/525 is set at 2.2 as opposed to the slightly higher 2.8 defined for PAL/625. This means that PAL/625 can produce pictures of greater contrast."
I would think that would depend on the actual gamma of one's display! Oddly enough the NTSC specification issued in February 1953 called for a gamma target of 2.5; this was changed after the final field tests that spring. The FCC has never enforced this part of the specification, and many engineers simply adjust gamma to make the picture look "right" on their chosen reference monitor.
I'm surprised you didn't mention another big difference between the NTSC system and current implementations of PAL and SECAM -- while the U.S. NTSC standard still calls for the color chromaticities originally defined in 1953, the EBU recommends a different set of primaries based on real-world CRT phosphors. Theoretically the NTSC system can reproduce a wider color gamut, but in practice the gamut is limited by the phosphors in the CRT so the EBU approach should give more accurate color rendition.
"Incompatibility between different versions of SECAM - SECAM being at least partially politically inspired, has a wide range of variants, many of which are incompatible with each other. For example between French SECAM with uses FM subcarrier, and MESECAM which uses an AM subcarrier."
MESECAM isn't a broadcast system at all -- the Middle Eastern countries are using SECAM B/G, which isn't really different from the system East Germany used to use. What happened is that VHS uses a drastically different recording system for SECAM, at least in France, than is used for PAL or NTSC -- instead of hetrodyning the subcarrier down to its lower frequency for recording, the FM subcarrier is divided by four and then multiplied back up in playback. MESECAM, on the other hand, is a cheaper but somewhat inferior system that uses the same hetrodyne conversion used in PAL; it's common in the Middle East, where users often receive both PAL and SECAM broadcasts from neighboring countries.
There used to be two different color sync techniques for SECAM, one using a burst on each line (like PAL or NTSC) and the other using a special waveform transmitted during field blanking, but the latter has apparently disappeared because those lines were needed for teletext.
"Beta is unique in having named the tape after the length rather than it prospective running time, thus making it free of the problems that beset other formats."
From 1975 to 1977, Beta tapes were numbered K-15, K-30 or K-60 to indicate the NTSC running time at Beta I speed (then the only speed available). The L numbering system was adopted in 1977 when the Beta II speed was introduced. RCA, which marketed the first two-speed VHS machines, tried to popularize its own numbering scheme based on the tape length in meters (the 246m T-120 cassette was called a VK250), but it never caught on.
Also, the new DV digital VCR format uses the same tape lengths for both the 525 and 625-line versions, since both record the same number of lines per second (240 active lines per field at 60 Hz, or 288 at 50 Hz, for a total of 14400 lines each second). Of course the 525 version runs just a hair longer than the rated time, but not enough to worry about.
"Actually, the last one - the camcorder, seems a bit of a surprise since it is camcorder footage that most often leads people into the morass that is TV system incompatibility in the first place. To be able to buy a camcorder that can record in PAL if you know you're going to send it to relatives in a PAL country, and NTSC if you're going to use it say in the USA would seem quite attractive to many people."
The big reason why camcorders can't be switched to different standards is that single-chip cameras have a stripe filter in front of the imaging device (whether tube or chip) to encode color information into the output. The camera uses two bandpass filters to recover this information before encoding it in NTSC or PAL form, and these filters have to be tuned to different frequencies for the 525-line or 625-line standards to match the spacing of the stripes. Using the same CCD imager for 525 and 625 is also problematic because the different line count would change the effective field of view of a given lens.