• MTS - Used in conjunction with NTSC/525. Consists of two independant carriers each carrying a discrete channel. One channel provides stereo sound by providing left/right channel difference signals relative to transmitted mono audio track. The second carrier carries the Secondary Audio Program (SAP) which is used for a second language or a descriptive commentary for the blind. Uses a technique based on the dbx noise reduction to improve the frequency response of the audio channel.
• FM-FM - dual carrier FM coded discrete stereo transmissions, analogue. Can be used for bi-lingual operation under user selection, but no auto-selection is available. Audio characteristics better than standard mono soundtrack.
• NICAM - (full name: NICAM 728) Digital two-channel audio transmissions with sub-code selection of bi-lingual operation. Stereo digital signals with specifications approaching those of Compact Disc are possible. NICAM stands for Near Instantaneously Companded Audio Multiplex and uses a 14bit sample at a 32KHz sampling rate which produces a data stream of 728KBits/sec.

• CC - (full name: Closed Captioning) Transmitted on line 21 of NTSC/525 transmissions, contains subtitling information only. CC has no support for block graphics or multiple pages but it can support 8-colours and the use of an italic typeface. Frequently found on pre-recorded VHS cassettes and LDs, also used on broadcast. Also found on PAL/625 pre-recorded VHS cassettes in a modified version.
• TeleText - An information service of 200-700 "pages" covering a wide range of topics including TV Schedules, News, Financial Market prices, Comment, Reviews, Concert & Theatre information. Subtitles are typically transmitted on page 888 in the UK, on pages 199/299/399 in Belgium and Holland, on page 150 in Germany and on page 777 in Italy. There are a number of variant character sets used, but the encoding is identical and all English alphabet characters plus numbers and most punctuation can be handled by any decoder. Includes support for 8 colours, and limited block graphics, and selective revealing of underlying TV picture. Transmitted on a variable number of lines (specified in header which contains basic information such as time, date and channel), starting on line 12 and continuing for 7-8 lines typically. Found on broadcasts and some LaserDiscs; recording of TeleText signals is marginal on S-VHS, almost impossible on VHS hence the PAL/625 version of CC.

 Overview

The first of these is what I loosely refer to as transcoding. This applies primarily to efforts to replay material from other TV systems using equipment designed with a single particular TV system in mind. Almost all of the solutions based on this technique are replay only and make no provision for the production of material in the foreign tv system.

The second approach is that of the true multi-standard equipment. These are pieces of video equipment that can work as fully operational pieces of equipment in any one of a number of TV systems. With a multi-standard video recorder, you expect an NTSC tape to be reproduced as a standard NTSC signal, and the same machine if fed with a PAL tape will reproduce it as a standard PAL signal. A multi-standard VCR can also be expected to make a perfectly normal NTSC recording of an NTSC input signal, and a perfectly normal PAL recording of a PAL input signal.

The third approach is that of standards conversion where the TV signal is actually converted from being a standard signal in one TV system to being a standard signal in another. This is the only way in which material can be sent from one TV system to another with an absolute garentee of working, and where operations such as recording and copying become possible in the destination TV system.
 

 Transcoding - Pseudo-PAL and Pseudo-NTSC

In the early days of television when everything was locked to mains frequency, it was next to impossible to get a TV to accept a signal with even the smallest instability. With the advent of switch mode power supplies and VCRs, there came both the ability and the need to decouple the field timing reference from the mains frequency. The reason for this was that the nature of video recording creates relatively unstable tv signals on replay, and as a result the TV has to follow the fluctuations and variations of the signal in order to reproduce the picture. The down side is that the field timing reference signal now has to be generated by dividing down the ticks from a quartz crystal, something that requires an increased component count in the TV receiver.

As time went by TV manufacturers tried to reduce the number of components by producing a dedicated VLSI chipset which did all the work. The majority of designs for these were actually implemented as a single chipset for the world, which would support either 525/60 or 625/50 pictures. It so happens that TV sets based upon such a chipset can actually produce a very acceptable monochrome picture of the other TV system when feed with such a video signal. The chipset will automatically adjust the number of lines in the picture to match those of the incoming signal.

Since PAL and NTSC are not that different in the way they encode colour signals, it's not actually that difficult to modify the signal to achieve a reasonable colour reproduction at the same time. The net effect is that you end up with a signal that has the frame rate/ scan line characteristics of the original TV system, but the colour coding and subcarier characteristics of the local TV system. This hybrid cannot be recorded but does provide a very effective way of painting over the cracks and allowing the reproduction of material in the other TV system.
 

 Multi Standard Equipment

If for example, you had a multi-standard VCR which supported NTSC and PAL, you could record the playback signal of an NTSC camcorder and make a genuine NTSC copy, or record an off-air PAL broadcast and make a genuine PAL VHS recording. What you could not do is to perform any kind of conversion; the VCR changes it's TV system personality rather than making any change to the signal. Any signal that is NTSC 525/60 will remain that way, and any signal that is PAL 625/50 will remain PAL 625/50. In order to make effective use of a multi-standard VCR, you will need either a multi-standard TV to display on, or a TV of each TV system you want to watch (as a general rule).

Multi-standard VCRs are not amongst the easiest things to find since they are not a mass-market item. Although most of the major VCR manufacturers do make them, surprisingly few actually distribute them on a world wide basis. As a result, other than in export markets such as those of countries such as Singapore and Hong Kong, they can only be found at a few specialist dealers and then often only as grey imports. The best advice would normally be to look for adverts in the back of a local video magasine, for example Video in the USA or What Video in the UK and parts of Europe.

While machines in the transcoding category are only available in a few major colour systems, there will be a multi- standard VCR for every country in the world. This does not mean that all multi-standard VCRs support all the world's TV systems, although some do. There are a number of multi-standard machines that support only the various 625/50 systems such as PAL/SECAM/MESECAM in use in eastern Europe and the Middle East. There are others that support PAL and NTSC but not SECAM, or maybe only certain versions of SECAM (usually MESECAM). Further complexities are added when you consider the capabilities of the TV tuners and RF adaptors of these machines, many of these support less combinations than the VCR itself can handle as video signals. A common example of this is the French SECAM-L; many multi-standard VCRs can handle this only through the video inputs and outputs, not through the Tuner and RF adaptor. To make a recording of French TV with one of these, you would need to attach it to the video outputs of a French TV and select the TV's tuner to the channel you want to record - not a lot of use if you want to do a timer recording.

In addition to being cautious and making sure that the multi-standard machine supports the TV systems you need, you also need to check for more advanced features, particularly stereo sound systems. Although there are a few exceptions, most stereo (VHS HiFi) multi-standard video recorders can only actually receive stereo broadcasts using one of the techniques, be it NICAM, MTS or FM-FM. In countries using the other systems, you will only be able to receive the mono TV soundtrack with these machines.

Finally, multi-standard machines tend to be fairly basic. Most manufacturers only offer about two models; typically one with only mono sound and one with VHS HiFi sound. Fancy extras like flying erase heads, manual audio record level controls, edit connections, and SuperVHS operation are not available. Neither are multi-standard camcorders. 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.
 

 Standards Conversion

Conversion between TV systems with same frame rate are usually reasonably effective, except of course that the resultant signal usually suffers from the deficencies of both the source and destination colour system.

Conversion between TV systems with differing frame rates is extremely difficult and there is no perfect solution. With a trained eye, it is possible to spot that any given piece of material has been standards converted within a matter of seconds. The units that perform these conversions are known as Digital Standards Converters. For many years digital standards converters were very expensive indeed and as a result were only used by TV stations and video facilities houses. This all changed in the 1990 with the launch by Panasonic of the NV-W1, a combination VHS deck/digital standards converter at around UK#1,600 (approx US$2300). Since then other manufacturers have also introduced domestic standards converters at even lower prices. Among the manufacturers with standards converters in their range are Panasonic, Aiwa, Sharp, and Samsung.

Professional standards converters also exist, many of which can achieve significantly better results, but at a price. One of the best is the DEFT, which costs a cool UK#65,000 (approx US$100,000)!