Hooray! you've finally got that 50-inch plasma HDTV you've been lusting for since the days when they cost a cool 10 grand. Excited with your same-as-cash, no-payments-for-a-year 1080p deal, you grab a beer, settle into the sofa, and tune in one of the games in DirecTV's NFL Sunday Ticket package, ready to watch the greatest image you've never seen.

But now that you have that HDTV, is the picture you're seeing actually high-def — or is it something less?

According to consumer Philip Kent Cohen, if you think you're seeing true HD just because you're watching a high-def channel on a high-def set, you're wrong. Two years ago, Cohen filed what he believes is the first lawsuit against bad picture quality. He's suing DirecTV, alleging that in its quest to provide as many HD channels as it can, the satellite company is squeezing too many signals into its limited bandwidth.

Some programming providers are running out of space. DirecTV, for example, says there's no more room for HDTV channels on its satellites. But it will launch two new birds later this year so it can offer more local digital broadcast stations, as well as hundreds of new HDTV channels — assuming it can find that many to license.

It's also true that picture quality is mostly about bits. All else being equal, the fewer transmitted per second, the poorer the picture. Without enough bits, images can dissolve into little blocks, especially during fast-moving action. That's not to denigrate the importance of pixels, because the more pixels, the sharper the image. The resolution of a 1080 image, for instance, is 1,920 horizontal by 1,080 vertical pixels, with the images shown progressively for 1080p and interlaced for 1080i. But not all HDTVs can display that many pixels, and many professional high-def cameras can't even record that many.

HDTV signals are broadcast over the air at up to 19 megabits per second (Mbps), but Cohen and others claim DirecTV's bit rate is often much lower than that. And Cohen's lawyer, Thomas Ferlauto, claims they've got the goods to prove it. "We've been able to measure the signal, and the bit rates are reduced," he says.

Lite at the End of the Tunnel
Cohen first noticed the problem when he checked out several high-def channels on his new Sony plasma set. Expecting a crisp image, he saw blockiness and softness instead. According to Ferlauto, when Cohen wrote to DirecTV to complain, "he received no response."

DirecTV believes there's nothing to discuss. "We have optimized the transmission of HD signals to provide our customers with the highest-quality video service," says a company spokesman. "DirecTV has always been about delivering superior-quality video, and we're certainly not going to compromise on that commitment with HD customers, who are our most discerning viewers. Our HD video transmissions are well within accepted definitions, but we can't account for a viewer's subjective notion of what constitutes a perfect HD picture."

Cohen isn't alone in alleging that program-service providers like DirecTV, Dish Network, and some cable systems reduce the bit rate of their signals so they can squeeze more channels through their pipes. Visit the AVS Forum (avsforum.com) and you'll find a lot of users complaining about the same thing. They call it "HD Lite." Some postings are even accompanied by still images from programs, comparing one taken from a DirecTV feed with one from a different source, like an over-the-air antenna or Verizon's new fiber-optic TV service, FiOS.

Pros and Cons
TV engineers acknowledge that satellite and cable services don't always transmit their signals at 19 Mbps, but many claim that's irrelevant. To preserve channel capacity, these services use a technique called statistical multiplexing (see below) that borrows bits from one channel on a transponder that's showing fairly slow-moving or static images and transfers them to another that needs a higher data rate, like a channel showing a basketball game.

This works because higher data rates are only needed for fast-moving action. Even on broadcast TV, "the bit rate is dancing all over the place," says John Turner, owner of Turner Engineering and a former National Association of Broadcasters Engineer of the Year. He says that an HD signal doesn't need to maintain a high bit rate all the time to look good. If the image is static, even 1 Mbps will produce a perfectly fine high-def picture.

Satellite and cable aren't the only places where you'll find lower bit rates. Although some broadcast networks demand that affiliates stick to 19 Mbps peak bandwidth when sending their HD signal to household antennas, not all stations do. A TV station that's splitting the high-def bandwidth to send out three or more sub-channels at standard-def in addition to the main, HD one just doesn't have the capacity to keep each of them at a high bit rate.

When Peter Putman, president of the broadcast-consultancy firm ROAM Consulting, checked the bit rates of WSTN in Syracuse, New York, he found that the three standard-def sub-channels were each using around 3 Mbps, while the main high-def feed was using just 8 to 13 Mbps. "When the camera panned across a crowd during a football game, small objects would turn into blocks," he said. His local Comcast cable system, on the other hand, eschews such bit-rate finagling. Each Comcast HD channel he's checked sends its signal at 17 to 18 Mbps.

Speaking in Codec
So, are these broadcasters trying to cheat us? Even though HDTV has been around for a while now, program providers are still on a learning curve. Putman thinks they don't realize that reduced bit rates compromise picture quality because everything looks fine in their control rooms. But the gear in a lot of control rooms is hardly state of the art. At a recent HDTV conference, Putman asked attendees what type of TVs they used to monitor images, and several said they had only 30-inch standard-def sets.

The critics think they see some relief on the horizon, however. Several claim that HD channels compressed with MPEG-4 — the advanced video codec DirecTV is using for new HD channels — look better than ones encoded with the older MPEG-2 standard. (MPEG-4 is designed to be more efficient than MPEG-2, needing only half the bit rate to deliver the same picture quality.)

But if some are seeing better pictures with MPEG-4, John Turner thinks it's just another example of the collective unconscious at work. "Unless you can quantify things, it's difficult to say ‘my picture sucks'," he says. "Digital TV is very complex, and many things can account for a bad viewing experience."

Turner believes that the broadcast networks and big pay-TV channels such as HBO have agreements that force program providers to send signals of the same quality as the ones they receive from the programs' creators. "If cable or satellite fooled around with this, they'd be cutting their throats," he says.

Turner has checked the bit rate DirecTV uses for its high-def signals and found nothing awry. The feeds from the major broadcast and pay-TV networks "have no reduction in bit rate," he says. "Anyone who says their resolution is no good doesn't know what he's talking about."

Yet Cohen is right when he says companies like DirecTV don't transmit 1080i HD in 1,920 x 1,080 format (DirecTV uses 1,440 x 1,080 instead). This wasn't an issue when most HDTVs could only reproduce images at about 1,000 pixels across and still isn't for 720p (1,280 x 720) sets or plasmas and LCDs with display resolutions such as 1,366 x 768 or 1,024 x 768. But today's fixed-pixel 1080p TVs can achieve full 1,920 x 1,080 resolution, making the picture on one of these displays less than optimal — unless you're using it to watch a 1080p Blu-ray Disc or HD DVD. In fact, whether you're seeing a degraded image or not depends on many factors, including the quality of the display, the performance of its deinterlacer and scaler, and the age and make of the encoders used at the point of signal origination.

While compression might leave legions of videophiles incensed, experts who track the issue think it's even less important than O.J.'s efforts to find the real killer. And so, apparently, does Philip Cohen. Despite his lawsuit, he hasn't canceled his DirecTV service and gone elsewhere. When it comes down to picture quality vs. content, content invariably wins. "The problem is, he's a big sports fan," says Cohen's attorney. "And DirecTV basically has the monopoly on the NFL."

EXPERTS DISCUSS COMPRESSION

JOHN SCIACCA
Contributing Technical Editor
Lead System Designer, Custom Theater and Audio,
Murrells Inlet, South Carolina

From my own experience, I would argue that high-definition signals from cable-TV providers tend to be more compressed than those from satellite. At my home in South Carolina, I have a 61-inch Samsung DLP set and Time Warner cable decoded by a Scientific Atlanta HD cable box. At the custom-installation showroom where I work, there's an identical Samsung set fed by a latest-generation DirecTV satellite receiver. I routinely watch identical programming on Discovery HD and HDNet, and I notice far more compression artifacts at home on cable — most noticeably macro blocking whenever there's fast motion. The picture also suffers similar artifacts if a number of objects are moving at the same time. Of course, whether you see the same things will depend on your equipment and your program provider.

SEAN GREER
Owner and Senior System Designer
Experience AV Home Theater, Montrose, Colorado

Don't forget to clean up your signal path before trying to evaluate signal-compression issues such as block artifacts (which occur when moving areas of an image like fire break up into red and yellow squares). What's the native resolution of the material? Are you trying to display a 1080i signal on a TV that has only 720 or 768 lines of resolution? If so, your TV's signal processor might be compounding — or even creating — the problem. Even if your satellite receiver has been set for 720p to match your set's native resolution, it's still processing the native 1080i signal into another (720p) resolution, which could be introducing distortion into your picture.

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