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News & Notes covers the DTV upgrade here (editorial).

Q & A

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1.  What is the Digital Television Transition?

The Digital Television (DTV) transition is a problem currently afflicting the United States. Existing Analogue broadcasting equipment and technology (STV) which works perfectly well and has certain advantages compared to DTV has arbitrarily been declared unsuitable by the Federal Government.

Since the majority of existing U.S. Television sets have analogue receivers these sets require conversion boxes to receive the new signal. Also, broadcasters have been required to purchase exceedingly expensive new transmission equipment to enable the digital broadcasts.

2.  Why does the DTV Transition Require new Equipment? the Color Upgrade did not

For the "NTSC" color TV upgrade a way was found to bundle the color information alongside the black and white information, this method is called YCbCr. In this method the Y (luminance) is derived from the existing black and white signal and the Cb (chroma-blue) and Cr (chroma-red) information are "squeezed" in alongside the Y transmission on a "sub-carrier" wave. The Green component needed to complete an RGB color image is matrixed out of the Blue and Red chroma information (via licensed witchcraft).

As a result of this, equipment that was not capable of decoding the CbCr information ignored it and decoded only the pre-existing Y information as a monochrome black and white image as before.

The digital transmission ("ATSC") is fundamentally altering the way that the image is encoded and decoded, thus existing decoding equipment in the receiver is now useless. It is necessary to intercept the digital signal and convert it into an analogue format to watch DTV on an analogue television.

3.  Why does The Vistua Network Organization Believe DTV to be Inferior?

VNS Organization does not believe DTV to be inferior per-se but rather believes that the benefit of DTV is outweighed by the financial cost, technical problems and inconvenience of deploying the new technology.

4.  What are the Purported Benefits of DTV?

DTV advocates make much of the supposedly improved picture and audio quality. While such measurements are subjective (witness negative audience reaction to removal of film-grain) image and audio information of greater resolution can indeed be transmitted

DTV advocates also make much of the availability of sub-channels within the DTV transmission, public broadcasting makes great advantage of this, deploying multiple sub-channels focusing on global news and information, arts and crafts, etc.

An additional minor feature is "datacasting" services such as electronic programming guides, vaugely similar to the ORACLE and CEEFAX type-systems that have been in use in Europe for decades.

5.  What are the Real-World Disadvantages of DTV?

Digitally encoded signals have unexpectedly different propagation characteristics compared to analogue signals. Signal propagation area drops of up to 50% have been reported although the drop-off normally seems to be less.

Digital signals are "all or nothing", whereas with analogue broadcasts, weak signal strength manifests as "fuzziness" or "static", which may be too slight to even notice, DTV signal weakness manifests as total disintegration of the picture and audio.

Digital transmission and production equipment is astronomically expensive.

All OTA transmissions are susceptible to "dynamic multipathing", a condition in which reflections of the waveform bounce off of flat surfaces or passing airplanes and become refracted and/or reach the receiver at slightly different times, in analogue television this manifests itself as "ghosting", the super-imposition of a slightly offset faint outline of the image. In DTV multipathing results in total image corruption.

Receivers situated very close to transmitter masts located at a greater height (such as upon hills or atop tall buildings) will suffer greatly from these problems.

Chyrons and other CG elements have perceptible compression artifacts around their edges. This is because the ATSC transmission standard includes an MPEG compression scheme.

The ATSC scheme inherits "interlacing" and all of its attendant problems, a great disappointment.

Inclement weather can lead to total loss of intelligible signal.

6.  What is the difference between DTV, HDTV/HD and DirecTV?

DTV refers to standard Over The Air Digital Television using the ATSC system standard in North America. It is free.

HDTV refers to any form of television which is broadcast in HD. HD is "High Definition", a very broad term for various A/V formats of higher than STV resolution. and most DTV broadcasts are in some form of High Definition. Cable and Satellite TV services can also be in HD, subscribers often must pay extra for this.

Some DTV channels promote themselves as offering HD television, when in reality some or all of their supposedly HD broadcasts, are nothing more than STV resolution programs stretched into HD size and format, this is effectively the same as the darkroom enlargement process that can be done on negatives, and has the same negative impact on the quality of the end product. Another technique used to pass STV programs off as "HD" is to frame the STV feed with animated side-bars to the left and the right, the combined image may be in an HDTV aspect-ratio, but the useful part of the image is not HDTV.

DirecTV is an unrelated satellite broadcasting system owned by Australian media-mogul Rupurt Murdoch's oddly mis-named News Corporation. It is a subscriber service, and offers HD channels. In spite of its deceptive marketing practices, DirecTV is not required to receive DTV.

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