Video Urban Legends

[Gregg Lengling]

never ends. Today's fast-changing AV scene constantly generates an ongoing flow of myths, legends, and other blather that either arises spontaneously or is deliberately manufactured to push the bewildered consumer toward a certain product or technology. I'll make a valiant attempt here to explode a few of these video urban legends, nevertheless secure in the knowledge that, like Don Quixote, I'll find an endless supply of new windmills just down the road.

1. Digital television (DTV) is the same as high-definition television (HDTV).

DTV is a term that applies to the ATSC digital television format adopted in the US. It can use a variety of resolutions, some of which are standard definition (480i and 480p), while others are high definition (720p and 1080i). Much of DTV being broadcast today is high definition, but it doesn't have to be. In short, HDTV is a form of DTV, but DTV can be either high definition or standard definition. The FCC DTV mandate pushing us to an all DTV future does not require HDTV, only some form of DTV.

 

2. Digital Cable is HDTV

Digital cable is a system adopted by cable companies to squeeze more channels into their available bandwidth. It is not HDTV (though you need digital cable service to receive a cable company's HDTV channels, if available). It is also technically different than standard-definition DTV. Whether or not digital cable looks better or worse than standard-definition DTV depends on a lot of factors, not least of which is the quality of the original source (how the program was shot, digitized, etc.).

Some cable companies do carry a variety of HDTV channels, and these are vastly superior to their standard digital-cable package. The fact that they usually group their HDTV channels into a separate premium (and higher-priced) HD package should make this obvious!

3. Satellite TV is HDTV

See #2 above. Satellite TV is all digital, but apart from that, the same comments apply.

4. DVD is high definition

There are people out there who actually believe this is true. I'm sure that doesn't apply to any UAV readers, who are aware that two new, competing formats are expected to bring high definition to the little optical disc sometime this year or next. Current DVDs are certainly digital, and they can look great even on a big screen, but their resolution is well short of high definition.

5. 1080p is coming! 1080p is coming!

Things start to get a little complicated here. A little background music, if you please.

At the 2005 CES in Las Vegas last January, several manufacturers were trumpeting the imminent arrival of 1080p to the consumer market. It's true that many new 1920x1080 video displays are expected to hit the market later this year, joining the few that are available now.

But here's the rub: current HDTV sources are all either 720p or 1080i. There is no 1080p source material available to the consumer. Those new displays will internally convert both of the available resolutions to 1080p to match their pixel structure. This isn't a bad thing. Most of today's high-definition digital displays are 720p or near it, and the finer pixel structure in those new 1080p displays will smooth out the image and minimize the visibility of the pixel grid—the so-called "screen-door" effect.

But upconverted material is not the same as material that is produced in 1080p and maintained at that resolution all the way to the display. Just how much benefit that might bring is hard to say, since most of us have little or no experience with native 1080p material. There has been a lot of talk about the possibility that the high-definition optical-disc formats, particularly Blu-ray with its huge data capacity, might offer 1080p (specifically 1080p at 24fps, otherwise known as 1080p/24), but there have been no announcements to date confirming any such thing.

So when a salesperson tells you all about the mind-blowing benefits of that new 1080p rear-projection set, keep the drooling to a minimum.

6. A DVI or HDMI link from a high-definition source is "uncompressed high definition." Oooooh.

No, it's not. At least not in the sense that it offers any image benefits. DVI and HDMI connections into a compatible digital display can—and often do—look better than an analog component hookup, but that's because the signal remains in the digital domain all the way from the source to the imaging elements.

HDTV is encoded in a highly compressed format called MPEG-2 for transmission to your high-definition terrestrial tuner, cable box, or satellite receiver. That compression is lossy; that is, a lot of data are discarded and can never be recovered. Your cable/satellite/terrestrial device then decodes that MPEG data stream into a form that your display requires to produce an image. Each original frame of information is recreated, but there is no more "real" resolution in the restored frames than existed in the MPEG compressed data. The system works because MPEG compression takes advantage of both the human visual system and the often-repetitive frame-to-frame nature of video. So while this decoded data stream is far denser than its MPEG-2 parent, it can never reproduce all the data that was present in the pre-MPEG source back at the station. That's no tragedy; the ATSC high-definition system works remarkably well. But too many manufacturers are sneaking that "uncompressed high definition" line into their press releases these days, suggesting that there is something special or new here.

There isn't. In fact, the high-density DVI data stream (which is also carried by HDMI) was adopted precisely because it contains so much data that it is impractical to make a consumer recorder that will contain it. In other words, it's one more layer of copy protection. The most common form of HDTV storage device on the consumer market, the hard-drive recorder, includes the drive in the same box as the tuner, and it records the MPEG data before they're decoded. On playback, the data are retrieved from the disc, decoded, and then sent on to the display. A low-density digital data stream never leaves the box.

7. The DVI (or HDMI) output of that new DVD player "up-scales video to high definition (1080i/720p) resolution."

The quotes in the above sentence indicate text lifted directly from a recent new-product press release. But remember that the information on a DVD is standard definition (see #4, above). Many new DVD players can generate a 720p or 1080i data stream from their DVI or HDMI digital output (though not from their component output, at least with copy-protected material). This data stream might work better with some projectors than a 480p link, but it is simply an upconversion with no added resolution.

This upconversion does gives you a 720p or 1080i source for your display, but when we refer to a resolution of 720p or 1080i, most readers take this to mean high definition. In this case, it is not. The only function of this upconversion is to produce a signal that matches a display's native resolution. This makes the display's job easier. It might also produce a better picture, but only if the DVD player can upconvert the signal from 480 to, say, 720 better than the display itself can. But in neither case will the result be a true high-definition source, which requires that the material be produced at 720p, 1080i, or 1080p in the first place.

There are other howlers out there; all we can do when we encounter one is to mash it down. But like a game of "Whack-A-Mole," another will surely pop up to take its place. More grist for the critics' mill. I'm sure you've heard the one about plasma sets requiring a periodic recharge...



Thomas J. Nortonhttp://www.guidetohometheater.com/thomasjnorton/305tjn/