Standardizing Standards

A show is being sent around the world. Everyone has agreed on the transmission standard. But in one country there's no audio, in another the picture goes black periodically and in a third the equipment says it's failing because it found something not part of the program at all.

Welcome to the real world, where standards are not necessarily all they're cracked up to be. It's not the flexibility or complexity of digital technology that has brought about a change in practices. In fact, there probably hasn't been a change at all, but we haven't noticed because of one highly standardized television broadcast standard.

"The number of lines has changed many times since 1934, and I hold the view that the 525-line standard may very easily be changed in the next few years." Those were the words of Dr. D. C. Espley of Britain's Institution of Electrical Engineers in 1945.

The learned Dr. Espley's view was the only rational one at the time. The first television system had eight scanning lines. When all-electronic television (lacking a mechanical spinning component in the camera) was first broadcast in England in 1936, it had 405 (total) scanning lines. When television was "introduced" to Americans at the New York World's Fair in 1939, it had 441 lines. The very engineers who came up with 525 lines also strongly considered 507.

As we all know, however, Dr. Espley was wrong. Television with 525 scanning lines has been broadcast for more than 65 years and is still being broadcast in almost as many countries. Although a few of those countries are converting to digital terrestrial television (DTT) broadcasting, 525-line programming is acceptable for (and is, in fact, being carried on) DTT broadcasts. Today, a scholar might conclude that 525-line television could easily last longer than 100 years.

So, was it a perfect standard? No, it was not.

By the time of Dr. Espley's statement, France had already moved to a higher line rate. And, when the FCC first approved color-television broadcasting in the United States, it was at a lower number of lines per frame and frames per second.

The second time the FCC approved color television broadcasting it was at 525 lines but at a lower frame rate--a tenth of a percent lower. That has led to such problems as rolling hum bars and time code incongruities. And there was another problem.

Comprehensive as the 1953 NTSC color standard was, it lacked a fixed relationship between the timing of the horizontal sync pulse and the phase of the color subcarrier. It's not that the relationship was disputed; it's just that no one felt there was any need for one.

Suppose you were standardizing pencils. You might consider their diameter, their shape, their composition, and even their color. But would you consider how they should pierce an apple? Why?

Similarly, when the second NTSC met to come up with a color standard, that subcarrier-to-horizontal-sync (SCH) relationship simply didn't even come up. There was nothing in the television broadcast world to which it might apply. After all, the first commercial videotape recorder was still three years in the future, and the color VTR was even further away.

Unfortunately, once the color VTR and, worse, color videotape editing became prevalent, that lack of a standardized SCH relationship led to ever-increasing horizontal blanking (or, to put it another way, shrinking pictures). This time there was a dispute about how to fix the problem.

It wasn't so much the relationship as the possibility of a standard the FCC might enforce before broadcasters were ready. The compromise was Industrial Electronics Tentative Standard No. 1, more commonly referred to as RS-170A (although there was never any such standard).

Then there was SMPTE 240M, another disputed standard. It gave us 1080-line HDTV's 1920 pixels per line. Unfortunately, it didn't give us 1080 lines; the standard called for 1035. HDTV equipment with 1080 lines came out before a SMPTE standard for it.

As for the global transmission at the beginning of this column, there are encoders and decoders from multiple manufacturers, with multiple users deciding they should do multiple things. More standards might not help.

Mark Schubin is an engineering consultant with a diverse range of clients, from the Metropolitan Opera to Sesame Workshop.