Questioning Technology: The Cliff Effect

Could the "cliff effect" become a Vietnam for American television broadcasters?No one quite knows yet, but some very smart television engineers are very worried about what might happen when the first new digital television stations go on the air in several major U.S. cities later this year.This little known twist in digital broadcasting technology (DTV) -- dubbed by engineers as the "cliff effect" -- means that viewers will either receive a perfect television signal at home or they will walk off the cliff and receive no picture or sound at all. Gone will be the days when a viewer can always get a fuzzy image on the screen with little more than a wire coat hanger.The cliff effect got maximum visibility at -- of all places -- a recent Sony press event in New York City. An odd forum, to say the least, since Sony is one of the world's major manufacturers of television sets. The public shot fired 'round the television industry came from Peter Dare, Sony's chief broadcast technologist, in answer to a reporter's question about reception of the new digital television stations in urban areas, such as New York City. The reporter wanted to know how well indoor rabbit ear antennas will work for city dwellers who cannot place conventional TV antennas on the roof of their high-rise apartment buildings.Dare's answer brought quite a few gasps from his audience. He suggested there's a good chance rabbit ears might not cut it at all for receiving DTV broadcasts. Not cutting it -- in DTV terms -- means no reception at all. as in a completely blank screen.Worse yet, a viewer might get a perfect picture one day and nothing at all the next. "If it rains or the trees get leaves, you may have a problem," Dare said. "If you are on the fringe and just a little above the (signal) threshold, I'd bet you'd lose pictures some days." One wonders how this might be explained to someone who just paid $7,000 for a new digital high definition (HDTV) television receiver.Another issue is multipath, a type of transmission interference in which the TV signal collides with itself, resulting from reflections off of buildings, mountains, the ground, etc. With the current analog television system, multipath interference shows up as double image "ghosts" in the picture. With digital television, however, multipath can cause errors in the received data. Rather than generating picture ghosts, multipath interference can cause a DTV receiver to go blank. This, said Sony's Dare, may be a problem in the coming months when DTV broadcasts begin.Worse yet, how will potential owners of DTV and HDTV receivers even know if they can get a reliable signal from broadcasters before they make the purchase? Without an onsite survey with an expensive piece of test equipment called a spectrum analyser, they won't. Even with a positive signal measurement, there's no guarantee that bad weather and the change of seasons won't cause the receiver to go blank later on, noted Dare.With these problems, why would anyone buy a pricey new digital television receiver that may or may not work? How is an urban consumer electronics store going to have a reliable source of high definition TV signals in order to demo the new sets for potential buyers? Short of an HDTV signal from a satellite source such as Hughes's DirecTV subscription service, the answer still eludes the television industry. "We don't have a good answer," responded Dare to a question at the Sony press event.Dare's comments caused surprise and shock among the public promoters of digital television, though his views were fully supported by his broadcast engineering colleagues. However, with the DTV sales season in full throttle, not one wanted to go on the record to express doubts about the new technology.One engineer noted that with all the sophisticated broadcast industry tests that have been conducted to date on the "cliff effect," no one knows yet exactly how it might play out in the real world. The only broadcasters who have delivered digital signals, he said, are the direct-to-home satellite services. That, of course, is a totally different technology than over-the-air broadcasting through an antenna on the ground.With billions of dollars on the line, the looming issue of consumer acceptance has some in the broadcasting industry worried. Home viewers have long suffered poor analog TV reception due to an unwillingness or inability to install a proper outdoor antenna. But these viewers now at least get a degraded picture. They'll have no such luck when DTV arrives.Another engineer suggested that the people on the hot seat who will hear from disgruntled viewers will be the broadcast station engineers, not the media executives, station owners and politicians who drove the political changeover to digital television. A huge broadcast industry educational campaign will be required, the engineer suggested, to embed in the public consciousness the idea that DTV will result in better pictures most of the time -- just not all of the time.Frank Beacham is a New York City-based writer and producer. Visit his web site at: Mail: 163 Amsterdam Ave. #361, New York, NY 10023. Email:


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