Digital TV At Last?
Analog TV broadcasting is set to end in two years, but its legacy could make the digital transition anything but smooth
Editor's Note: We are posting this feature from our February 2007 issue because the transition to DTV has been back in the news.
February 17, 2009, is D-day -- when the term "digital divide" will take on a whole new meaning unrelated to computer access. That is when the nation's 1,700 analog television stations will shut down in the long-promised changeover to all-digital broadcasting. Cable and satellite viewers or those whose TV has a digital tuner will be able to watch CSI and American Idol unaware that anything has changed. But the 21 million households using a conventional set with rabbit ears or a rusty roof antenna -- typically people who are poor, elderly or living in rural America -- will turn on their TVs and see ... nothing.
Not since color made black-and-white sets passe has a new technology so compelled consumers to replace their primary entertainment appliance. In contrast to the variable radio waves of analog broadcasting, digital TV (or DTV) uses electrical pulses to transmit information precisely and efficiently. Thus, DTV offers startlingly sharp pictures, capable of revealing individual blades of grass on a field or the writing on a ransom note held in a fictional detective's hand. DTV also will enable new interactive features, thanks to its ability to pack enormous amounts of information in scarce bandwidth. For instance, it could let viewers viewers call up stats on a ballplayer during the game or view a recipe from a cooking show. Broadcasters will be able to offer even more channels in the available bandwidth, too. The freed-up space will make room for better communications for public safety agencies during emergencies such as hurricanes and for next-generation cellular services.
Several thorny technology issues remain, however. Even after the end of TV broadcasting as we have known it, analog TV's legacy will be with us for years to come. While analog-retentive households contemplate the grim reality of no TV at all, others who seem to be digitally outfitted will still experience stumbling blocks. Cable systems, which are already set up for DTV, may not actually be able to deliver purely digital signals, because many of their customers' older "cable ready" sets still have analog-only tuners. And even in areas where digital is already available, it has experienced service hiccups: picture problems and even clogged bandwidth. Perhaps it is more accurate to say that long after 2009, viewers will encounter a series of digital divides, between analog and digital and among different kinds of digital.
The idea of switching the country to digital TV first gained momentum in Congress during the 1980s, when the legislature became aware that Japan already had high-definition TV, albeit produced by an analog system. (There has been much confusion over the difference between DTV and high-definition television, or HDTV. HDTV is simply the sexier subset of DTV, and it has a few special requirements: more bandwidth to deliver it, extra capacity to store it, a higher-resolution screen to show it and a larger display to appreciate it.) The U.S. government proceeded to run a series of tests with competing manufacturers designed to determine a next-generation broadcast system. The initial results showed that high-definition broadcasting was not practical without compression -- and the most important thing to know about digital is that, unlike analog, it compresses video extremely efficiently. So the idea of retrofitting analog broadcasting for greater resolution was abandoned.
The Advanced Television System Committee, working with an alliance of companies that initially had incompatible systems, ultimately succeeded in unifying a standard. The consortium authorized 18 DTV formats, two of which -- 1080i and 720p -- are high-definition and meant for viewing on wide screens. The 1080i format puts 1,080 lines on the screen by transmitting the odd lines, then the even lines, and interlacing them. Hence the "i." The second puts 720 lines on the screen one after the other -- that is, progressively. Hence the "p." (In contrast, analog broadcasts offer up to 480 horizontal lines.) Debates over the merits of each are confined to broadcast engineers and videophiles, who cite the spatial advantage of displaying more lines (1080i) versus the temporal advantage of showing fast motion (720p). Most viewers do not care.
The first publicly available high-definition broadcasts in the U.S. began in 1998, as HDTV sets started going on sale. In the late 1990s stations were expected to give up their analog frequencies by 2006. But that plan fell through because too few people bought the expensive digital TVs or the set-top boxes for receiving the signals and because high-definition programming rolled out slowly as well. NBC, for example, offered only one series in high definition, The Tonight Show, beginning in 1999. It took another five years before the network showed all its prime-time dramas and sitcoms in 1080i. Broadcasters had little incentive to give up their analog frequencies. Compared with DVD, a home video format introduced just a year earlier that became the most successful new product launch in consumer electronics history, HDTV barely registered in sales or public awareness.
In March 2005, when manufacturers met in Washington, D.C., at an HDTV summit, there was still no definitive cutoff for analog broadcasting. But in early 2006 President George W. Bush signed a law compelling a transition in just three years. What changed? The name of the legislation was a clue. It was called the Deficit Reduction Act of 2005. The government expects to raise billions of dollars when it auctions off much of the 108 megahertz (MHz) of "returned" analog frequencies. Other factors that make analog's demise more likely this time are that DTV tuners are now mandated in all new TV sets with a screen size of 25 inches or larger (and will be required in all sets, regardless of screen size, by March 1 of this year), most prime-time network series and all major sports events are broadcast in high-def, and most cable systems carry from four to a dozen high-def channels (although that number still represents a mere fraction of their overall channel lineups).
The Long Good-bye Some argue that the cessation of over-the-air analog TV by federal law will be far more disruptive than when color elbowed black-and-white aside in the 1960s. After all, those silvery tubes continue to work even today. That will not be possible with conventional TV sets unless they have a digital converter box. Adding boxes, which are expected to cost about $60 for a no-frills model, to every TV in any given household could be an expensive proposition.
According to the National Association of Broadcasters, the 21 million homes that receive only over-the-air signals own a total of 45 million TV sets. If you add that figure to the 28 million second and third TVs in homes with cable or satellite where only the primary set is hooked up to the pay service, some 73 million TVs nationwide could go dark on D-day. (Because many of those secondary sets are attached to DVD or video game players, they will not necessarily become useless just because they cannot receive broadcasts.)
To take the financial sting out of the changeover, Congress has authorized the U.S. Commerce Department's National Telecommunications and Information Administration to spend up to $1.5 billion on subsidies. Starting in 2008, those who cannot afford a box will be eligible for two coupons worth $40 each toward their purchase. To record an over-the-air signal, older VCRs and DVRs will also have to be attached to a conversion box, although by July 1, 2007, any new device sold that includes a tuner (DVD player/recorder, DVR, computer TV card) must include a DTV tuner.
Even if your TV can receive over-the-air digital signals, that does not guarantee you can see the pictures. Analog offers what is called "graceful degradation": people in fringe reception areas can at least see something, even if the picture ghosts or fades in and out. DTV is not as forgiving. You either get it, or you do not.
Analog TV transmits a complete picture 30 times a second, a lavish waste of bandwidth from a digital perspective. Digital compression, on the other hand, is based on the premise that it is only necessary to transmit reference frames and intermittent changes. That is how the same 6 MHz allocated to a single analog TV channel can accommodate up to six standard-definition digital channels or perhaps one HDTV channel. But it also explains why momentary signal losses can be so disruptive to DTV reception. Without the luxury of analog redundancy, a DTV set may freeze up on the last reference frame it received, or the picture may break into a less than gorgeous mosaic or just go black. There is nothing graceful about any of those glitches, especially if they happen as the killer is revealed during a crime show.
And you do not have to be living in a valley 80 miles from the broadcast tower to feel abandoned by a DTV signal. Multipath reflection continues to be a problem within a city; the receiver gets multiple versions of the same broadcast because it bounces off buildings. The U.S. uses a transmission standard called 8-VSB (for 8-level vestigial sideband), which is more susceptible to signal woes than the European standard COFDM (coded orthogonal frequency division multiplexing).
Today's receivers can better compensate for this problem than ones manufactured at the dawn of DTV, thanks to more powerful processors. Newer receivers are using higher-performance chips capable of calculating a greater quantity of reflected signals and discarding them more quickly than the processors in earlier-generation DTV receivers [see "The Multipath to Clarity," by Philip Yam; Scientific American, June 2005]. But viewers may still have to reposition an indoor antenna when they switch to a channel coming from a different direction -- a frustrating exercise that recalls the days before most homes had rooftop antennas or cable. While multipath is DTV's Achilles' heel, the problem is restricted to a small portion of the 15 percent of American households not subscribing to cable or satellite service. Although there is something to be said for commercially supported "free" TV, more HDTV programming (including premium movie, sports and nature channels) is already available by subscription only than from over-the-air DTV, and the gap will likely increase.
Dual Broadcasts Until d-day, over-the-air stations will continue to simulcast analog and digital signals on their two allotted frequencies of 6 MHz apiece -- the federal government has given stations the extra space for digital during the transition period. The DTV frequency lets broadcasters do something they could not do with analog: multicast several programs at the same time. Whereas a station might choose to allot the entire 6 MHz to high definition, it could instead transmit several channels in standard-definition digital. One standard-definition channel could be accommodated around the clock -- even when the station is carrying the network's HDTV programs -- without a significant degradation in quality, the National Association of Broadcasters claims.
Those consumers whose signals travel by cable still will not escape analog after 2009. Operators would like to go all-digital because viewers prefer watching the high-definition version of a channel if available. Not only does an HDTV program's wide-screen format fit their new TVs' 16:9 aspect ratio, not to mention their old pair of eyes, better than standard definition's 4:3 shape, but they also can pick out much more detail. If CSI's mantra is to follow the evidence, then HDTV's two million pixels (on a 1920 x 1080 screen) point the way. The rising demand for high definition has, however, already become a problem for cable and satellite operators, who have a finite amount of bandwidth to divide among various channels and services.
It does bother me a little that all the cursing I sometimes do in my keynotes is going to become part of my story, yet I have to embrace it because that's just how my DNA expresses itself when I'm onstage. I want to be proud of what I do.