Hi-Res vs. Hi-Def? The Answer is in the Starz!

[Gregg Lengling]

You might not have noticed that HDTV is great, and that's a problem. I don't mean that it's a problem that you ain't noticed that HDTV is great. Most folks who've seen good HDTV think it's pretty danged great, and I figure most of you lovely readers are in that category. So you already know HDTV is great, and, therefore, you ain't part of the problem.

No, the problem is that HDTV is great. Don't take my word for it. TV Technology alumnus Walt Ciciora was ranting about the problem recently in some cable-TV-related publication that ain't as good for wrapping fish as this one is (smaller, thinner pages with ink more likely to smear all over the scales).

Here's his message to cable ops: You're now delivering HDTV. Subscribers with HDTVs will see HDTV. They will like it. They will then call to complain about the quality of everything else you deliver.

I'll do a little song and dance on that there quality in a moment, but first here's some proof that Walt is right. There has been a danged staggering quantity of HD programming for cable announced recently. There's ABC, Bravo HD, CBS, Comcast Sports, Discovery HD Theater, ESPN, Fox, Fox Sports-I'm tired, and I've only gotten to "F."

Anyhow, if I'd kept going through the alphabet, somewhere after Showtime I'd have mentioned some new HD channels from Starz! I'm not excited. Starz! comes with its own built-in exclamation point. That's some new HD channels plus something called a "Hi-Res" channel.

"But, Mario, what's the difference between HD and Hi-Res?

It's simple, really. HD stands for high definition, which is an entry in a dictionary on a ladder. Hi-Res requires a working knowledge of Latin; it means "Hello, thing," which is what Gomez used to say on "The Addams Family."

Methinks that's enough scholarly research. It's time to get back to TV technology.


WHAT'S NORMAL?

Starz! kind of defined its Hi-Res when it announced it at the big cable convention in Chicago this year. It'll be 16:9 at 5.6 Mbps with around 720 active pixels per line. They showed it compared to HD (higher bit rate and pixel count), and methinks there weren't too many folks who couldn't tell which was which. But that ain't the point.

What they should have compared it to is normal cable programming. Walt asked how're you going to keep them down on the farm after they've seen HD. Some of you fine readers might've interpreted that as a call to compare HD (which, even in the 720p flavor, is 1280 x 720) to SD, which we all know to be 720 x let's call it 480.

In the last paragraph, I waffled on the vertical resolution (which could be 480, 483.5, 486, or even 576, if we're talking the eastern shore of the great Atlantic pond). But two paragraphs ago, I waffled on the horizontal resolution (I know all you astute readers caught my "around 720;" I hope you get well soon).

As you devoted readers know, the ATSC, in its infinite wisdom, didn't pick Rec. 601's globally accepted 720 active pixels per line for the U.S. digital-TV standard. The ATSC did pick 720 for its non-U.S. standard, but that's a story for another millennium. No, the ATSC picked 704 for the U.S. digital-TV standard on account of MPEG requiring unremaindered divisibility by 16 for macroblocks.

"But, Mario, 720 is evenly divisible by 16!"

Right you are! And, while I'm pointing out mathematical anomalies, I might as well mention that 1,080 ain't cleanly divisible by 16.

The problem ain't exactly with 720. It's with half of 720.

I mean, back in the 1940s, when cable-TV was getting started, the issue was picture quality. After HBO started the satellite revolution in the 1970s, the issue became picture quantity. How many channels can be squeezed into one (or sometimes more than one) cable?

In analog, there's a pretty simple formula. One channel is 6 MHz. Divide the bandwidth of the system in MHz by 6 and you've got a good idea of the channel capacity, as long as you ignore such problems as triple-beat interference.

Got a 360 MHz system? Figure 60 channels tops. Pushing 750 MHz? It's maybe double that.


DO THE MATH

Now, then, I'd be hard-pressed (like those waffles I talked about earlier) even to name 120 channels, but I'm just a non-existent figment of my publisher's imagination, so what do I know? Besides, there's video-on-demand.

Pick 20 hit movies. Start each of them every five minutes. That'd be 20 x 24, which is -- carry the pi -- 480 channels, or about four times the capacity of the whole cable system. No, no, that will never do at all.

So let's get digital (sing it, Olivia!). With 64-QAM, the payload is about 27 Mbps in a single 6-MHz channel; with 256-QAM, it's about 39 Mbps.

Uncompressed 10-bit 4:2:2 SDTV is 270 Mbps. Drop to eight bits and dump the blanking intervals, and you're down to about 166 Mbps, still uncompressed. D-9, DVCPRO50, and IMX at its highest rate are 50 Mbps-compressed, but pretty danged good. DV, DVCAM, and DVCPRO are 25 -- small enough to fit into a 64 -- QAM channel and still look mighty fine. Betacam SX is 18 Mbps; stick two videos in a single 256-QAM channel. That's still going to look very, very good to a civilian viewer.


DIGITAL FOR THE MASSES

The best SDTV the civilians have got at the moment is DVD. That's 4.7 GB per single-layer, single-side disk. That's 37,600 million bits per disk. Let me call it 36 billion for convenience.

There are 3,600 seconds in an hour, and two hours in many movies. That comes to 5 Mbps.

If digital cable kept SDTV to 5 Mbps, they'd be able to get at least five programs into a 64 -- QAM channel and seven into a 256 -- QAM channel. That'd be in the neighborhood of 600 DVD -- quality channels for a 750 -- MHz system.

Sound like enough to you? Poor, innocent, naive reader, besides video-on-demand, there are also cable modems and cable telephony, not to mention other potential moneymakers.

The data rate could be halved to 2.5 Mbps, but that might show blocking artifacts due to bit starvation. So some cable video gets its Hi-rez halved.

360 ain't evenly divisible by 16, but 352 is. 352 x 2 is 704. Lo and behold! (Someone told me what lo means, but I forgot; I'm pretty sure it's got nothing to do with J-Lo). The reason ATSC picked 704 was on the theory that cable would adopt 16 -- VSB instead of 64 -- and 256-QAM. But cable didn't.

Now, then, you might want to consider that Starz! Hi-Res channel in a new light (3,200 K of course). On an ordinary, letterboxed cable channel, you might get a movie that's just 352 x 360 (what's left when you letterbox 480 at 16:9) at around 2 Mbps; on the Starz! Hi-Res channel you get 720 x 480 at 5.6 Mbps. Methinks that's a bigger difference than going from the Hi-Res to the HD.

Starz! is absolutely right that the 5.6 Mbps of their Hi-Res channel is one whole heck of a lot less than the 18 Mbps or so that some figure HD ought to be, so you can get maybe three Hi-Res programs in the space of one 18 Mbps HD (two in the space of a 12 Mbps HD).

But there's just a wee mite of a hint of a suggestion of potential trouble brewing in paradise.

You see, quality readers, the same cable people to whom Starz! is planning to offer its 5.6 Mbps programming are the ones who came up with halving resolution and data rate in the first place. The only thing keeping 5.6 from becoming 2.8 is that true HD stuff that makes everything else look lousy. But, come the revolution, 5.6 Mbps is going to be among the first to go.


Mario Orazio is the pseudonym of a well-known television engineer who wishes to remain anonymous. You can e-mail him at Mario_Orazio@imaspub.com