Why digital TV ?

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shillyard
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Why digital TV ?

Post by shillyard » Mon Oct 23, 2006 4:36 pm

I don't understand the reason behind digital TV. A CRT cant produce a picture from digital information. So why produce video in digital just to send it to a DAC. It makes sense in a computer but not in a TV, at least no to me. Now I do understand a DVD will store data or video with no loss until you do physical damage to the disk . But for broadcast I don't understand this.
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FOLLOW THE MONEY TRAIL

Post by jollyrgr » Mon Oct 23, 2006 4:59 pm

FOLLOW THE MONEY TRAIL

It is as simple as that. There are several reasons for digital:
  • Broadcasters can control what you watch, how long you can copy it and save it (if at all). A digital set can be made such that you cannot change the channel during a commercial.

    The FCC gets to auction off all the analog spectrum no longer being used by analog TV stations. They get $$$ from Motorola, Cingular, Verizon, and other services to use the spectrum. TV and AM/FM radio spectrum cannot be charged for.

    There is some rumor that every house hold will get ONE OTA (Over The Air) tuner "rebate" check. In other words you buy a tuner for ONE TV and the government will send a rebate check for the approximate cost of the tuner. Have more than one TV? TOO BAD!!! You must buy the tuner or a new set.

    Many of the normal functions of your set will be lost for OTA as the set will have to be tuned with an external tuner. Want those functions back? Time to buy a new TV. Thus there is a new rush for TVs (yeah, right).

    So no rush to buy new TVs or tuners, what is next? You and hundreds of thousands of people not using cable or satellite pay services will now have to subscribe so that their old sets work. Remember: only the OTA broadcast signal must be digital signals; pay services like DirecTV, DISH, and cable TV DO NOT HAVE TO SWITCH the ANALOG output of their receivers off. Yes, the satellite services are already digital as are most cable stations. But their output will still be the same ANALOG signal called NTSC.

    Thank the greedy politicians and the broadcasters stuffing their back pockets for this change.
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Post by hp » Mon Oct 23, 2006 5:00 pm

Digital TV allows much more data to be encoded in the signal (including much higher resolution) then conventional analog broadcast.

When the color NTSC specification was devised, it was meant to be compatiable with older technologies, such as b/w tv. This signal can only carry a resolution of less than 640x480. This is very low compared to modern HDTVs (which can reach 1920x1080P).

A large portion of modern TVs are not CRT based. Many use plasma, LCD, TFT, and other technologies which have to be digitally driven. There is no point to feed these high resolution displays with old and outdated analog signals.

Harrison

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haklesup
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Post by haklesup » Mon Oct 23, 2006 5:14 pm

Many reasons.


1. The seperation band between channels is smaller so you can fit more channels in the same band. This is because a digital system can reject more noise.

2. The image of the picture is much better resolution. To get that resolution in Analog would require a significant increase in channel bandwidth.

3. Digital video comes with digital sound which has its own list of advantages. For example I don't think you can transmit 6.1 audio in analog. You have to use one of the older Dolby compression methods to get close.

4. Many Analog TVs (particularly with PIP) do already convert the video to Digital in an intermediate processing step.

5. with error checking of the incoming data possible, traditional forms of interference are obsolete. Say goodbye to multipath, weak reception and static'y audio among others.

6. Advanced services which we have yet to see are possible. New types of simulcasting as well as interactive TV/Internet applications may eventually appear.

7. Broadcasters get more channels to put programming on within their alloted channel. They can choose what mix of resolution and program material to put on.

Finally your assumption is incorrect. Though a CRT uses Analog Drive signals, LCD and plasma are true digital. In all cases, the digital signal is transmitted and recieved by analog circuits. For the most part, the draw is better resolution and the promise of more applications but it definately was not to make the circuits simpler.

In a way, its stuff like this that drives the economy.

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Post by jimandy » Tue Oct 24, 2006 4:40 pm

There is one problem that the industry is still grappling with. Over distance analog signals will fade and become snowy but you can still see (and hear) something until noise overcomes. With digital, however, you have the "cliff effect" when your picture simply drops dead if there is too little signal strength or too much multipath distortion. For rural folks they may have picture one minute then absolutely nothing the next. In downtown apartments you may have to constantly futz with antenna positioning to get any picture at all. Rabbit ears will become a thing of the past.
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Post by jollyrgr » Tue Oct 24, 2006 7:20 pm

jimandy wrote:There is one problem that the industry is still grappling with. Over distance analog signals will fade and become snowy but you can still see (and hear) something until noise overcomes. With digital, however, you have the "cliff effect" when your picture simply drops dead if there is too little signal strength or too much multipath distortion. For rural folks they may have picture one minute then absolutely nothing the next. In downtown apartments you may have to constantly futz with antenna positioning to get any picture at all. Rabbit ears will become a thing of the past.
I've played with digital signals from satellite for some time now. There is a cliff effect to be sure. But there is also the "snowy picture" with digital. A digital TV picture will pixelate and you will see blotches form in the scene and will hear pops similar to a skipping CD when the signal gets weak. During high winds with a big dish you will see a fine picture on analog. With super high winds you might lose the signal. Any significant wind (20MPH or so) will shake the dish and distort the picture and sound for a while. You will see squares form all over the picture. Hard rain and large thunder storm clouds will cause this as well. During blowing ice storms or blizzard conditions watching something like Dish or DirecTV gets real interesting.
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Post by Robert Reed » Tue Oct 24, 2006 8:43 pm

The "cliff effect" to be sure. I have one station in my area that broadcasts on digital. In an hour long drama show the signal will ocasionaly drop completly - no signal, blank sreen. This will usually occur during the last 5 minute punchline segment, leaving you forever wondering how the show ended. It seems the cliff effect is directly proportional to the most important part of a show or news broadcast. At least with analog I can still make out a snowy picture and get decent sound. With all the hoopla over digital, I still prefer analog for reliability.

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Post by Dean Huster » Wed Oct 25, 2006 5:41 am

I've never had high winds affect my DirecTV signal. Clouds don't either. It's the rain and snow that's produced and swirls around in the cloud cover that's the killer. Snap, crackle, pop and pixelate to be sure -- IF you're getting a signal at all. The wife HATES it when it does that, totally ignoring the 99.999% of the time it doesn't and she's got 2,356 channels available that can't be had OTA.

There is something to be said about analog's resolution, however. With a digital system and a large, near-black or uni-color area, you can see the "paint-by-number" effect as the system can't decide to go up or down by a single bit. Analog doesn't do that, mushing everything together into a nice, pretty picture.

Give me the electronics of 1963 any day.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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Post by bodgy » Wed Oct 25, 2006 5:47 am

You might need a better quality lead in cable and possibly antenna.

If you live in a dodgy reception area with analogue, you'll just love to hate digital if you keep the same aerial system.

You'll either get no reception or freeze frame effects with nice loud pops and squeaks and whistles as the DS processors try to make the picture intelligible.

The cable will need to be upgraded to a low loss type with better foil/insulation if you have a long run or live in blocks of flats whereby a master antenna is used and distributed by the building management.

Colin
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Post by jimandy » Wed Oct 25, 2006 4:39 pm

In the "tornado alley" area of the South, my area of Alabama in particular, rural folk depend on TV stations like ones in Birmingham and Montgomery for warnings and tracking. Of course, when weather like that threatens there is also rain and wind before and after. Sure those folk can listen to radio but it's the high powered, low channel (2 - 13) stations with their high towers that have the broadest coverage. When OTA stations go digital I suspect reception under such circumstances will be iffy and the government subsidized tuners will be useless.
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Post by haklesup » Thu Oct 26, 2006 11:18 am

That's why its a blessing to have an NTSC and ATSC tuner. When the digital becomes unreliable, I just flip over to the NTSC channel. That won't be an option forever though.

I suppose that problem is moot with cable and reduced significantly with satellite which in the future, the majority of us will be using anyway. I use the airwaves now becauase cable charges extra for the same channels I already get for free but that should change. Eventually most cable channels will be digital or HD and there won't be a premium to recieve them.

It's also likely that more sensitive tuners with better error correction will reduce the cliff effect in the future. Its a logical avenue for development, there's still hope.

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Post by bigkim100 » Sun Oct 29, 2006 6:07 am

To be quite honest ....no matter the technical reasons, the reason that jollyrgr gave is the real reason. My good old-fashoned 42 in analogue tv hooked up to digital cable is crisp, clean, with ZERO noise, snow, pixellation, etc...no matter what the weather.

Oh....and dont hold youir breath for government rebates on receivers, when your government cant even get its act together on other really important things... like inexpensive prescription medication...and the war.
Kim..The man with the cute little girls name...and Frankensteins face and body.

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