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Getting in Tune with DTV

Mar 1, 2001 12:00 PM, By Peter H. Putman, CTS

What you need to know to pick the clearer tones and sharper images of high-definition broadcasts.

The introduction of digital television service in the United States has started on a sour note, with missteps, bumps, and false starts since 1997. One of the big reasons is the slow acceptance of DTV by the general public, which often views DTV as something happening in a parallel universe.

The vast majority of DTV broadcasts are only available as terrestrial signals, and information about scheduled DTV broadcasts is hard to find. Only a select few viewers can get the signals over cable, and the satellite offerings are limited to a couple of premium channels. DTV stations are slow to get on the air, and when they do, they are often running far less than their authorized power levels.

To add to the confusion, there are a plethora of TV sets being advertised for sale that are supposedly “DTV capable,” “DTV-ready,” and even “HDTV-ready.” Instead of a small yellow RCA plug for video, we now have to deal with three wires colored green, blue, and red. Unless, of course, we happen to be looking at DTV set-top boxes (STBs) and TV sets that use the computer-standard 15-pin VGA connectors.

If it weren't for the explosive sales of DVD players, DTV might very well be dead in the water. No one can account for the phenomenal sales of DVD players, but there's no question they are a hot consumer video technology.

Thanks to DVD, the average consumer has learned about and now understands such arcane concepts as progressive-scan video, component video connections, widescreen anamorphic video, and Dolby digital audio. Guess what? Those are all building blocks of the new DTV standard.

It's not as difficult as you might think to watch DTV signals. If you happen to live in one of the top 30 TV markets, you probably have at least one DTV station on-air, and more likely have two or three. DTV broadcasts are on the same VHF and UHF TV spectrum as analog broadcasts, and in some cases channels within the same city are adjacent to each other.

Right now, the majority of DTV stations are broadcasting in the UHF (500MHz to 800 MHz) band, and it will remain that way once DTV is fully implemented (supposedly by January 1, 2006, but don't hold your breath). There are selected allocations in the VHF band, and some stations are already negotiating with the FCC to retain their old VHF channels after the analog-to-digital changeover.

So, what TV sets are available to watch DTV and HDTV signals? Before we get into that, let's review some of the DTV basics.

DTV 101

The new digital television standards in the United States encompass a wide variety of digital signals. You've probably heard about the 18 different Advanced Television Systems Committee (ATSC) broadcast formats, but in reality there are just four: interlaced 4:3 video with 480 scan lines (480i); progressive-scan video with 480 scan lines (480p); progressive-scan video with 720 scan lines (720p); and interlaced video with 1080 scan lines (1080i).

The first two formats, 480i and 480p, are considered Standard Definition Television (SDTV) because they don't offer any more picture detail than we can get now with our analog 525-line system. The next two formats, 720p and 1080i, are considered High Definition Television, as they deliver much more picture. 720p and 1080i are also 16:9 widescreen formats. (It's possible to transmit 480i and 480p 16:9 formats, but these remain SDTV in any case.)

The number “18” in the ATSC Table 3 standards is derived from different vertical refresh rates as well as square and non-square pixel formats. For home reception, the standards you'll encounter will be 1080i/30 (1080 interlaced lines, 30 Hz refresh rate), 720p/60 (720 progressive lines, 60 Hz refresh), 480p (480 progressive lines with either 60 Hz or 30 Hz refresh), and 480i (480 interlaced lines with 30 Hz refresh).

These signals are all transmitted as compressed 4:2:0 MPEG-2 streams, complete with audio and Program and System Information Protocol (PSIP) data. This stream of data is modulated onto a radio frequency carrier using what's called the Eight Level Vestigial Sideband (8-VSB) system, which cannot be received by a standard TV set. The maximum permissible data rate is 19.39 Mb/s, so as to fit within our legacy 6 MHz TV channels.

To receive and decode 8-VSB signals, at the minimum you'll need an ATSC-compliant DTV set-top box. This device connects to your antenna (or cable, if you have 6MHz DTV channels available that way) and decodes the digital information, splitting it into video, audio, and available data streams. (An integrated DTV set will have this tuner and perform the same functions.)

Even though DTV signals are 100% digital, the video and audio are usually fed as analog signals from the set-top box (except for Dolby 5.1, which usually connects through optical or coaxial cables to your audio system). The DTV video format is always component and never composite or S-Video.

The standard implementation is sync-on-green, usually labeled “YPbPr.” In this system, the picture sync travels on the luminance or “Y” signal, and color information on the Pb and Pr color difference signals. In order to watch these SDTV and HDTV signals without any additional conversion, you'll need a monitor, TV set, or projector with broadband component video input jacks.

Even though YPbPr is the ATSC standard video format, some manufacturers have chosen to output their signals as RGBS or RGBHV, two formats that are closer to the computer display world than DTV. The advantage of this format is that you can often use a standard computer monitor to watch the signals. The disadvantage is that many consumer DTV sets won't support RGBS or RGBHV.

All set-top boxes output stereo audio, and include at least one Dolby digital connection. On the simplest level, all you need is to hook up the component cables and stereo audio through RCA jacks, and you can watch DTV and HDTV. How it will look is another matter, and that depends entirely on the type of monitor, TV set, or projector you select.

Product confusion reigns supreme

Because there are so many ways to watch DTV signals, manufacturers were bringing products to market and labeling them without regard to any acceptable standard. For example, a TV set with component inputs might be able to display interlaced DVDs, but not show any progressive-scan DTV signals.

Similarly, a portable projector with RGB inputs might have a horizontal scan rate fast enough to display a 720p or 1080i HDTV signal, but not size and position them correctly if they're connected in an RGBS or RGBHV format.

The Consumer Electronics Association (CEA) released a new set of definitions in late August of last year to help consumers understand the differences between TV sets and monitors.

Special logos are to be placed on these products to help consumers quickly distinguish between a digital set that receives ATSC broadcasts, and a video monitor that requires a set-top ATSC tuner to decode the broadcasts. Here's how the definitions break down:

• High-Definition Television (HDTV) defines a fully integrated television receiver that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats. In addition, it will display 720p or 1080i active vertical scanning lines in a 16:9 aspect ratio. It must also receive and decode Dolby digital audio, or pass it through for decoding.
• High-Definition Television Monitor is a direct-view or rear-projection monitor that can be connected to a DTV set-top box and will display 720p or 1080i active vertical scanning lines in a 16:9 aspect ratio. To meet the definition of HDTV, the monitor must have true vertical resolution to show at least 540 progressive or 810 interlaced picture lines.
• High-Definition Television Tuner is an RF receiver that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats. It must output the 720p or 1080i/p formats with minimum active vertical scanning lines of 720p, 1080i, or higher. Additionally, it may output HDTV formats that are converted to other signal formats, with lower-resolution ATSC formats (480i and 480p) output at those levels. (The output can also be 100% digital at full resolution.) It must also receive and decode Dolby digital audio, or pass it through for decoding.
• Enhanced-Definition Television (EDTV) is a fully integrated television receiver that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats. It must have enough active scanning lines to meet at least the 480 progressive (480p) standard or higher, but does not have to support the 16:9 HDTV aspect ratio. It must also receive and decode Dolby digital audio, or pass it through for decoding.
• Enhanced-Definition Television Monitor is a direct-view or rear-projection monitor that can be connected to a DTV set-top box and will display at least 480p active vertical scanning lines, with no specified aspect ratio.
• Enhanced-Definition Television Tuner is an RF receiver that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats. It must output the 720p or 1080i/p formats with a minimum of 480 progressive vertical scanning lines. Alternatively, the output can be a digital bitstream capable of delivering 480p, while 480i can be output at native resolution. It must also receive and decode Dolby digital audio, or pass it through for decoding.
• Standard-Definition Television (SDTV) is a fully integrated television that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats to “produce a usable picture.” It can have less active scanning lines than an EDTV set. No aspect ratio is specified, and it must receive at least an analog audio signal.
• Standard-Definition Television Tuner is an RF receiver that will receive any and all ATSC terrestrial broadcasts, and will decode all of the ATSC Table 3 formats. The output signal may be in the form of NTSC video, or S-Video. It must also receive and decode Dolby digital audio, or pass it through for decoding.

Have it your way

As you can see, there are numerous ways you can watch DTV signals. The catch is when there's an HDTV broadcast, which by definition means a 16:9 720p or 1080i signal displayed at true resolution. The majority of available TV sets, monitors, and front projectors use 4:3 aspect ratios for imaging, so the image may appear letterboxed with black bars on top and bottom.

In reality, all you really need is an electronic display with the correct horizontal and vertical scan rates, plus component inputs, to watch DTV and HDTV signals. The DTV scan rates (31.5kHz for 480p, 33.75kHz for 1080i, and 44.9kHz for 720p) are well within the range of most multiscan computer/video monitors.

The 1080i standard has a great deal of support from Japanese manufacturers, and even ultraportable LCD projectors will recognize and correctly present 1080i material in a letterbox format. Older monitors will also recognize this format. I use a somewhat-ancient NEC MultiSync XM29 at home as an “air check” monitor for DTV reception, and it automatically syncs up and sizes 1080i RGBHV signals.

The 720p standard is a little trickier, as it largely originated on these shores. Many monitors and projectors will not size this format correctly in RGBS/RGBHV mode, as they think it is either an SVGA or XGA computer source. Newer models are now including support for 720p, provided the signal is connected as three-wire YPbPr. Some plasma monitors are now available that are “format agnostic” — just tell them the image aspect ratio and select the appropriate component video format, and you are in business.

The 480p format seems simple to handle with its 31.5kHz scan rate, and it is when connected as a YPbPr signal. Unfortunately, many projectors and monitors assume this is a VGA signal when RGB connections are used. If the source is 16:9, it may be compressed into a 4:3 window and you won't be able to re-size it. The widespread adoption of 480p DVDs is helping to correct this problem.

I use other displays to watch DTV signals. A Sony VPH-D50HTU 7-inch front projector (very format agnostic) can display any DTV signal in the correct aspect ratio, provided the projector is converged and set up correctly. Sony's VPL-VW10 HT LCD projector is another popular choice for DTV, as it has native 16:9 LCD panels (1366×768 pixels) and recognizes all ATSC formats as long as they are connected to YPbPr inputs.

I have a Princeton AF3.0HD 32-inch 16:9 monitor to view HD material. This monitor supports all ATSC formats without conversion, and although it prefers them to be connected as YPbPr signals, it will correctly size and center DTV signals in the RGBS and RGBHV formats. The two Sony projectors and the Princeton monitor would qualify as true HDTV displays, while the NEC monitor is strictly EDTV.

Standards questions

Right now, there is still a considerable amount of debate over the DTV standard in this country. The 8-VSB standard has not proven as robust for indoor reception as originally expected, and some voices (led by Sinclair Broadcasting) are calling for the United States to adopt the European COFDM DVB standard. Obviously, the antennas and receivers have to be improved, and steps are being taken in that direction.

In the foreseeable future, 8-VSB will be the DTV standard in this country. If you want to watch DTV signals, the most logical way to do it is to use a separate DTV set-top box and a compatible HDTV, EDTV, or SDTV monitor or projector. (Once the DTV signal is decoded from 8-VSB or COFDM, the signal format is the same — YPbPr or RGBHV.) The box can be upgraded or changed without having to replace the TV.

At home, I use a pair of Panasonic first-generation STBs (TU-DST50 and TU-DST51) to watch DTV programs. Both decode and pass all ATSC signals at their native resolution, including 720p. (Many tuners do not pass 720p and instead up- or downconvert it to 480p or 1080i.) The output of both tuners is in the YPbPr format, and I use an Extron CVC 200 format converter to change the signal to RGBHV for the NEC MS29 monitor.

Many manufacturers are now selling (or getting ready to sell) DTV set-top boxes. The earliest models were terrestrial-only receivers (also cable), but all the new models (except one) are combination terrestrial/satellite receivers, which cuts down the risk of unsold inventory. RCA was the first to sell an integrated terrestrial/satellite receiver, the popular DTC-100. Even though it outputs RGB and converts all progressive-scan signals to 540p, this STB has sold more units than any other model.

As a result, new combo STBs are coming to market from Mitsubishi (SR-HD400 and SR-HD500), Panasonic (TU-HDS20), Sony (SAT-HD100), Zenith, Toshiba, Princeton (HDT-2000), and Samsung (SIR-S60), to name a few. Most are available for $1,000 or less. In addition, Samsung announced a new terrestrial-only STB for $699 (SIR-T150) at the recent Consumer Electronics Show.

You can also watch DTV on your PC, although the products to chose from are limited. Hauppauge Electronics offers the WinTV-D Digital TV tuner PC card ($299), which lets you watch all ATSC format signals simply by connecting an antenna. The catch is that the output signal is always 480p, although you do have selectable aspect ratios.

Another recent PC-DTV entry is the Hi-Pix PC-DTV card ($399), which also allows you to receive and watch ATSC-format signals on your computer. Unlike the WinTV-D card, this version outputs a higher-resolution signal and can record the MPEG-2 bitstream directly to your hard drive for later viewing.

The list of HDTV, EDTV, and SDTV TV sets and monitors is too big and detailed to include here. Both conventional and direct-view DTV TVs and monitors are available from Panasonic, Hitachi, Mitsubishi, Sony, Samsung, Zenith, Sampo, Konka, RCA, Princeton, Toshiba, Sharp, Pioneer, Philips, and JVC. Rear-projection sets (using tubes) can are offered by Sharp, Panasonic, Mitsubishi, Sony, Pioneer, Samsung, Zenith, Hitachi, Runco, RCA, Philips, and Toshiba.

Want a flat-matrix screen? You can get plasma from Sony, Pioneer, Runco, Hitachi, Fujitsu, Philips, Panasonic, Sampo, Samsung, Sharp, ReVox, and Zenith, to name a few. LCD monitors capable of SDTV, EDTV, and even HDTV display are available from Samsung, Sampo, Zenith, Sharp, and Sanyo.

LCD rear-projection TVs are now sold by Sony, Samsung, JVC, and RCA, among others. Finally, Texas Instruments' DLP technology is now available in rear-projection TVs sold by Panasonic, Mitsubishi, and Hitachi, and front-projection versions were shown at CES by Toshiba, Sharp, and PLUS.

Where do I start?

If you are ready to take the plunge into DTV, there are a few websites with useful information to check out. Etown at www.etown.com has a comprehensive list of products and reviews, plus a regular schedule of DTV and HDTV programming updated every 10 days. CBS has its schedules available at www.cbs.com/hdtv, and PBS lists its schedule for the next few months at www.pbs.org/dtv.

Another good source for information is the AV Science website at www.avsforum.com, where there are thousands of discussions going on about everything from set-top boxes to antennas, DSS reception, programs, TVs, monitors, and projectors. I've posted several articles about terrestrial reception at www.projectorexpert.com, which may be helpful if you need more information about signal reception.

Don't Ask Me Why

DIGITAL TELEVISION IS ALIVE AND WELL, BUT YOU'D NEVER KNOW IT

My local DTV market in Philadelphia is one of the most active DTV markets and has been since 1998, with seven stations currently broadcasting.

There's only one problem: Hardly anyone knows about it!

Seeing HDTV for the first time is a revelation. After my HDTV Super Bowl party this year, I heard several guests mutter things like “pushing my old TV off the roof” on their way out the door. Even with a weak signal, the picture quality is top-notch — no ghosts, noise, or smeared colors.

Do you enjoy PBS programming? The recent Piano Grand concert from the Smithsonian Institute looked pretty good on regular TV, but was spectacular in 1080i HDTV. Are you a fan of NYPD Blue? It's now available in 720p every Tuesday night, complete with Dolby 5.1 surround sound.

Enjoy Jay Leno on The Tonight Show? It's available in 16:9 1080i five nights a week on NBC. Did you follow the AFC football playoffs and Super Bowl? CBS broadcast them in HDTV, and will show the US Golf Open in HDTV in June. Can't miss an episode of Ally McBeal or The X-Files? Fox has ‘em on in widescreen SDTV every week.

Now some bad news: Don't expect to find these listings in your local paper. Even though these are regularly scheduled DTV broadcasts, area newspapers and TV guides have yet to add any mention of these programs to their schedules. That's too bad, because Philly area viewers are really missing out on a good thing.

The rollout of DTV has been slow, and it will take a concerted effort by manufacturers and broadcasters to speed things along, just as RCA did in the '60s. RCA's sponsorships resulted in color TVs replacing black and white sets, so that people could watch Bonanza, The Wonderful World of Disney, and Star Trek in color.

Because consumers aren't getting enough information about DTV, the average viewer assumes there aren't any programs to watch. Au contraire! I've been watching DTV for more than a year now, but I've had to search on the Internet and check out network websites to find schedules for these programs.

Right now, the only way you can receive these local DTV broadcasts is with an outside or inside antenna. DTV channels won't be available on cable until the cable industry, broadcasters, and regulators agree on modulation standards and settle their differences over the “must carry” rule (understandably, cable operators don't want to carry two broadcasts from the same local station).

If you are one of the early adopters who's been watching DTV, why not take a few minutes to write to your local newspaper and ask that it print the schedules of HDTV programs — even a small “HDTV” logo alongside a listing would be sufficient. The more people know about DTV programming, the more likely they'll be to buy DTV receivers and monitors. It's a matter of supply and demand. --PHP

Continue the discussion on “Crosstalk” the Millimeter Forum.
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