Standardizing the Unstandardizable - TvTechnology

Standardizing the Unstandardizable

You might not have noticed that Don Quixote is alive and well and working in Washington, D.C. And here's an even more amazing statement: This here lunar cycle I ain't gonna poke (too much) fun at my pals at the Consumer Electronics Association (CEA).
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SOMEWHERE OUT THERE You might not have noticed that Don Quixote is alive and well and working in Washington, D.C. And here's an even more amazing statement: This here lunar cycle I ain't gonna poke (too much) fun at my pals at the Consumer Electronics Association (CEA). Matter o' fact, I'm gonna end up agreein' 100 percent with their position on DTV receiver standards, to wit, that there shouldn't be any.

But first, this important note about CEA's erstwhile parent, the good ol' Electronics Industries Association (EIA). Methinks I've already ranted on this topic, but - what the hey, eh? One good rant deserves another (and, drug-addicted animal-lover that I am, I want to leave no tern unstoned).

THE FINE PRINT

It's gettin' harder 'n' harder to find composite-color NTSC gear at that good ol' show of shows, NAB, but give it a try. When ya find it, have a look at the specs. I can pretty much guarantee that somewhere or other, in the fine print, it'll say it complies fully with EIA-170A, RS-170A, EIA RS-170A, or even EIA/TIA-170A.

"Mario, what's so special about that? Everyone knows what 170A is."

Ayup, I'll pretty much go along with ya there. Everyone knows what 170A is supposed to do, which is, compared to 170 without the A, to provide a defined relationship between the color subcarrier burst phase and the horizontal sync phase. I ain't as convinced as you that everyone knows exactly what that relationship is nor how you're supposed to measure it.

But I imagine most folks think they know how to look it up. Ayup, just grab a copy o' EIA-170A, and ... Whuzzuh? Oh yeah, I nearly forgot: There ain't any such a thing as EIA-170A. Everyone agreed on what the standard oughta be, but the standard was never approved (and I'll give a free lifetime subscription to TV Technology and a chance to see yer name in print to anyone who can correctly tell me why it was never approved).

Anyhow, that's water over the dam or under the bridge if'n it ain't spilt milk, so there's no use cryin' over it (unless you're lookin' for that there phase relationship, in which case have a gander at EIA Industrial Electronics Tentative Standard No. 1, November 1977, or good ol' SMPTE 170M). Nah, I'm more into a different EIA standard this mensual ish: 250 (-A, -B, -C - you pick it).

Good ol' 170 - even the illusory 170A - is just a format standard. Ya got 525 total lines? Check. Is the HBI 10.9 us? Check. Stuff like that there.

PICTURES AND SOUNDS

My pal 250, on the other hand (where I still have five fingers) is a quality standard. Not meetin' 250? Then the pictures and sounds ain't great.

Geez! Why am I startin' on 250? I should go back to the VU meter, good ol' IEEE 152-1953 (and predecessors).

In the beginnin', Al Bell supposedly dropped some acid (ooh!) and said, "Hey, Watson, ol' buddy, gimme a hand here," or words to that effect, and the rest is history. Um - well, the rest woulda been history but for the invention of the variable-gain amplifier.

So, uh, like, where do ya set it at? So a buncha folks got together 'n' figured out the VU meter. Whatever ya may think of its benefits or deficiencies, the VU meter was a mighty big boon to broadcast technology.

EIA-250, NTC-7, and other stuff like that there is just a continuation o' the work o' the VU meter committee. Hey - what's the NTC in NTC-7 stand for anyhow? It's the network transmission committee. And, until pretty danged recently, all o' them there standards were pretty danged useful. Then came bit-rate reduction, a/k/a digital compression.

All bets are now off. A pal o' mine in the network transmission biz used to tell a story about some old NEC DS-3 video and audio codecs he was usin' for some circuits. One of 'em couldn't hack 250 short haul. Not much can give ya a 67 dB video SNR. Have a look at the specs o' your Digital Betacam or D-5 to see what I mean. But it still made great pictures and sounds.

PLAIN BUSTED

The other one was just plain busted. It could repeat scannin' lines, but it couldn't hack real video. Stick a full-field test signal in, and ya got a full-field test signal out. I dunno how it got around the 67 dB spec (maybe it didn't hafta do short haul), but my buddy swears it passed 250 with flyin' colors. Any time ya stuck real video into it - any real video (and I don't mean just RealVideo) - it barfed its brains out and couldn't pass diddlysquat.

Moral o' the story: When dealin' with bit-rate reduction, normal video 'n' audio tests don't mean squat. Some folks are tryin' to come up with useful tests for objective measurements, like the Tek PQA 200 and the Fraunhoffer audio jobbie, but the best most of us can do for the nonce is to use our eyes and ears.

If'n it looks and sounds good, it is good; if'n it looks and sounds bad, it is bad. And I don't give a flyin' patootie what the so-called "objective" tests show. With bit-rate reduction, you can have the world's greatest multipulse response and SNR and chrominance non-linear gain and still have sucky pix. Ditto for THD+N, SNR, IMD and the other usual single- or two-frequency-at-a-time audio tests.

Anyhow, I didn't come here to preach Tek's PQA and PQM nor Audio Precision's multitone nor anythin' else like that this here moon. Nah, I woke up ol' Bossie and punched her keyboard so's to tell ya that I agree with CEA.

Now, then, there ain't one whole heck of a lot that I happen to agree with CEA about. For instance, I don't happen to agree with them that somethin' should be called a "digital television" if'n the only thing digital about it is its channel numbers and the fingers that push the buttons on its remote control. Call me old fashioned, but I happen to think that somethin' called a "DTV" oughta at least pretend to be able to receive DTV transmissions. There, I've said it.

SEEING EYE-TO-EYE

There's a lot more, methinks, where CEA 'n' I don't exactly see eye-to-eye (yeah, I know, CEA ain't got any eyes, but I - or we - don't really exist, so we're even). But there's one DTV-related issue on which See-ya and I are in complete cahoots, and that's DTV receiver standards. They don't want 'em; neither do I.

"So, Mario, who does?"

Gladja asked. Lemme see now ... There's NAB. There's MSTV. Methinks there are a coupla-three networks or so. Maybe even a person and a half at Our Beloved Commish. Folks like that there.

I'm in cahoots with those folks, too, leastwise as far as the fact that all existin' 8-VSB receivers don't seem to be able to hack real-world urban receivin' any too well. Lemme see now ... There were the Sinclair Baltimore tests, the Motorola field tests in Philadelphia 'n' Washington 'n' San Francisco, the NxtWave field tests in Philadelphia, the Wallace tests in Washington, the CBS tests in New York - geez! - how many independent tests do we hafta do before everyone agrees that there's currently a problem with urban reception o' VSB?

NO PROBLEM

Ayup, I know the routine: "There's no problem with VSB, Mario, only with the receivers that have been tested." Well, pals, that's how come I included Motorola's and NxtWave's field tests in my list in the last 'graph. In case ya just got back from bein' thawed outta a block of ice, lemme point out that Motorola and NxtWave are manufacturers of advanced 8-VSB demod chips with suped-up equalization. When they were announced, methinks the press releases used phrases to the like of "make multipath a thing of the past" or "eliminate concern about multipath" and so on and like that there.

So give a read to the Motorola field test reports. Hey - leastwise they were honest. The failures were caused by multipath interference.

Now, then, here comes the interestin' part. I made sure in that there paragraph listin' the tests to note that they were field tests. In the lab, methinks, both Motorola and NxtWave have pretty much proven they can handle the next Deluge and Pillar of Fire, let alone mere multipath, without battin' a gate.

Matter o' fact, Zenith has been runnin' some interestin' demos. The first set was at CES, the second set was in good ol' Washingtoon, D.C., and methinks there's a-gonna be a third set at NAB. Now, then, these Zenith demos most definitely were not field tests. They didn't even receive off-air DTV signals outta the field. They wired VSB and COFDM modulators to receivers via processin' equipment that could add noise, multipath (static and dynamic), impulses and other bad stuff like that there.

(By the by, have ya ever noticed that at the great CES, the consumer-electronics show, no one ever receives any DTV signal directly off air? They all get 'em from an advanced cable head end with channel processors and delays and stuff like that there. But - hey - whaddu I know?).

BLOODY MURDER

Anyhow, some folks have been screamin' "Bloody Murder!" over some riggin' they say Zenith did, like usin' 8 MHz COFDM stuff compared to 6 MHz VSB or supposedly overloadin' the COFDM receiver front ends or supposedly stickin' impulse-noise generators next to the COFDM stuff. I'm gonna give 'em the benefit o' the doubt in this here piece. Any company that came up with the wireless remote control can't be all bad.

The Zenith results - surprise! - showed VSB to be superior to COFDM, even with various kinds o' multipath interference. Now, then, before ya go blamin' Zenith, keep in mind that NxtWave's and Motorola's lab tests also came out with good results. And, whatever else ya might think o' Motorola or its products or philosophies, ya gotta hand them an honesty award. The field test data they published showed that their own chip couldn't hack it. So, I, for one, believe that their lab tests show that the chip could hack it.

So, what's goin' on here? Well, DUH! Field conditions are more complicated than lab conditions. No, really?

For all I know, there really ain't any problem with VSB urban reception, even though all the existin' receivers can't hack it. And what, pray tell, were those receiver designs based on? Lab tests.

So, here's NAB and MSTV tellin' us that we've gotta have receiver standards. Uh-huh. Maybe they have to deal with 0 dB ghosts that are close in? Maybe they've gotta do dynamic ghost ensembles at 5 Hz?

Hey - whatever it is, Zenith has probably already done it in its demos, and Motorola and NxtWave have done it in their labs. And they all passed summa cum laude (which is Latin for "better'n not-bad-at-all").

IN A NUTSHELL

So, what are those supposed reception standards gonna give us? In a nutshell: a new RS-250 for analog TV reception just as we're enterin' the digital age. In other words, zilch, zip, niente, and zero.

What we need is the Tek PQA of DTV reception, somethin' that truly figures out what field conditions are like and tests for 'em. Trouble is, outta the thousand or so sites where there have been VSB reception problems, there have probably been 2,000 or so different conditions.

DTV reception standards ain't gonna solve diddly squat. Ya can go the CEA route and just hope receivers get better (I believe they will, but I ain't gonna place any bets on the date when they get good enough), or ya can go the Sinclair route and try to change the transmission system. Another piece of paper - especially an RS-250 of analog reception in the DTV era - just ain't gonna hack it.

There, there, Bossie. You go back to sleep now, just like those folks lookin' for the DTV reception standards.