Multichannel TV Sound - 1950s Style

[Synchrodyne]

This is split from a digression in the thread “Sony PAL to NTSC converter”, https://www.vintage-radio.net/forum/...050#post695050.

Originally Posted by winston_1

I knew about 819 in Algeria, but not about bilingual sound. Do you have the technical details as to how it was done?

The information that I have comes from a brief item in Wireless World 1957 March, attached, which describes a simple decoder. There was apparently a description of the technique itself in WW 1957 February, but I have not been able to locate that issue.

Anyway, it appears that the decoder involved switching a sound IF valve on and off using a quasi-square wave at line frequency, phase-shifted π/2. The “on” period could be switched to correspond with either half of the line frequency sine wave from which the quasi-square wave was derived.

This I think implies what was essentially a time-division multiplex system, with the AM sound carrier switched at line frequency between the two audio channels. This would generate sideband clusters at odd harmonics of the switching frequency. Possibly only the first harmonic set was transmitted. In that case it could also be seen as a frequency division multiplex system using a sum signal for the baseband and a difference signal for the subcarrier.

I imagine that typical receiver sound IF channels had sufficient bandwidth to accommodate the additional subcarrier sidebands. Perhaps though, noise limiter (where fitetd) time constants would need to be arranged so that the subcarrier was not seen as noise. System E line frequency was 20 475 Hz, which indicates that the maximum AF frequency that could be used was around 10 kHz, probably viewed as adequate back then.

Actually, I am surprised that an analogue TDM system provided sufficient separation between uncorrelated AF channels. In later TV analogue multichannel sound systems, whilst sum-and-difference multiplexing was used for stereo, separate FM (sub)carriers were used where they were required to carry a second audio channel. Thus in the Japanese FM-FM system, the FM subcarrier was used either for the stereo difference channel or the second audio program. In the American MTS system, the stereo difference channel was carried on an AM subcarrier, whereas the second audio program was carried on a separate FM subcarrier. In the German Zweiton system, the second FM carrier was used either for stereo (R channel generally, but difference channel for the Korean version) or the second audio program.

Anyway whilst the Japanese FM-FM system, used from 1978, is generally regarded as the first TV multichannel sound system, the French “AM-AM” system, as used in Algeria, predated it by at least 21 years.

The WW 1957 February article, if it can be found, should provide more detail and should deny or confirm my own deductions. I first saw mention of the French system in WW 1959 October, which referred back to the 1957 issues.

Cheers,

[winston_1]

Interesting. I'll ask around and see if I can locate the Feb 1957 article.

By the way the Japanese system was in use before 1978. In 1972 I backpacked around Japan and remember TVs in youth hostels that could be switched to English sound during the news, and recalling crosstalk from the Japanese sound. I asked around and soon discovered that either bi-lingual or stereo could be transmitted but was unable to get technical details of how it was done. It was many years later (actually about 7 after I joined the BBC) that I found the details.

[Synchrodyne]

Thanks for that. I hadn’t realized that the Japanese FM-FM system had been in use for that long. I have a couple of references, attached, that mention 1978, but it does not surprise that NHK, and maybe others had been using it on a trial basis for a long time before that.

I agree that information on this and like systems was hard to find back then, and to some extent still is. I don’t think that I have yet seen a full specification for the Korean version of Zweiton.

I can recall the crosstalk on hotel TVs in Japan back in the late 1980s. As far as I know the Japanese TV setmakers generally stayed with intercarrier sound in the early days of the FM-FM system, with one or two using split sound for higher quality. That may be why for example the Sony VTX-1000R TV tuner (American version) had split sound with an intercarrier sound backup for cable channels suffering from ICPM. On the other hand the European-oriented VTX-100ES (Zweiton) had QSS using European ICs. It would appear that QSS SAWFs did not become available in Japan until 1982.

I also noticed crosstalk on Korean hotel TVs in the 1990s. At the time I had assumed that Korea had followed Japan and was using the FM-FM system; it was later on that I discovered that it had in fact adopted a modified Zweiton system.

Cheers,

[Synchrodyne]

I have another reference to 1978 as the official start data for the Japanese FM-FM system. But it also suggests that it had been available for some time before that. This is in the book “Radio Receivers”, edited by William Gosling, Peter Peregrinus (for IEEE), 1986; ISBN 0-86341-056-1.

From page 421 therein: “The FM-FM system has been used in Japan since late 1978. Its use was considered in Europe by several broadcasters in the early 1970s, but it was found that the two-carrier system was slightly better than the FM-FM system under conditions of multipath reception such as are found in mountainous regions.” Draft parameters for the System B/G/H version of FM-FM were provided, from a Swedish proposal. As I recall, in the event the Swedes also bypassed Zweiton and opted for the digital approach.

Cheers,