Why is SD content better via Cable Box, compared to regular SD from wall coax? - AVS Forum
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post #1 of 13 Old 06-14-2012, 06:53 AM - Thread Starter
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SImple question. I just bought a new HDTV, and I tested the SD channels both ways:

Method 1) Connected the TV directly to wall coax cable, and tuned all channels. HDTV channels picked up, as well as SD channels.
Method 2) Connected the TV to my TWC cable box, auto tuned all channels. HDTV channels picked up, as well as SD channels.

The difference is that the SD channels look TERRIBLE on method 1, whereas they look quite good with method 2. One looks real fuzzy, almost as if lower resolution. Like a really bad YT video. The other looks comparable to DVD quality, slightly less.

Realistically, I only have (and only want) one TWC digital box in my house, and that is in the basement HT room. For this other TV (family room) I was hoping to just connect to the wall. But the SD content looks so bad, this is not going to be acceptable.

Anyone have an explanation as to why SD channels can look so differently between the 2 methods?

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post #2 of 13 Old 06-14-2012, 07:31 AM
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Anyone have an explanation as to why SD channels can look so differently between the 2 methods?
Obviously there are two different processing chains here. You don't mention if your SD is analog or QAM. If they're Analog the TV's tuner is inadequate. If digital then it's likely the cable box is applying some kind of temporal filtering to the video when it processes it, which your TV isn't.
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post #3 of 13 Old 06-14-2012, 10:42 AM
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Do the SD channels have problems when just using the cable outlet from local broadcasters and are they in analog or digital format? You can use the INFO button on your TV's remote to find out what resolution it is receiving from the source you are using.
Do you use different PQ settings for the connectionn from the wall outlet that use for the connection from the set-top-box?
Does your TV have both an analog and a digital signal input connector?
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post #4 of 13 Old 06-14-2012, 12:21 PM - Thread Starter
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Not sure if my SD is Analog or QAM. Dont even know if my TV has a QAM tuner... !
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Originally Posted by olyteddy View Post

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Anyone have an explanation as to why SD channels can look so differently between the 2 methods?
Obviously there are two different processing chains here. You don't mention if your SD is analog or QAM. If they're Analog the TV's tuner is inadequate. If digital then it's likely the cable box is applying some kind of temporal filtering to the video when it processes it, which your TV isn't.

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post #5 of 13 Old 06-14-2012, 12:27 PM - Thread Starter
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SD channels seem to have no problem connecting my TV directly to the wall via COAX cable. The signal from SD channels appears to be analog, based on the description on the INFO menu. The HD channels say 1080i and say Digital. The SD Channels say 480i and Analog.

Same PQ settings on both inputs for sure, I set them to match, even though one could potentially have them different.

The TV has digital connectors (HDMI) as well as Analog connectors.

My two scenarios are:
(1) Wall coax jack -> Coax cable -> TV Coax input.
(2) Wall coax jack -> Coax cable -> Digital Cable box coax input -> HDMI cable -> HDMI input on TV.

Thanks for any help. I was wondering it maybe the TVs internal 'tuner' is just terrible at SD signals, whereas the Digital Box tuner is better at SD signals? The difference I am noticing is substantial, just to be clear.
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Originally Posted by walford View Post

Do the SD channels have problems when just using the cable outlet from local broadcasters and are they in analog or digital format? You can use the INFO button on your TV's remote to find out what resolution it is receiving from the source you are using.
Do you use different PQ settings for the connectionn from the wall outlet that use for the connection from the set-top-box?
Does your TV have both an analog and a digital signal input connector?

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post #6 of 13 Old 06-14-2012, 01:14 PM
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Originally Posted by gnolivos View Post

SImple question. I just bought a new HDTV, and I tested the SD channels both ways:

Method 1) Connected the TV directly to wall coax cable, and tuned all channels. HDTV channels picked up, as well as SD channels.
Method 2) Connected the TV to my TWC cable box, auto tuned all channels. HDTV channels picked up, as well as SD channels.

The difference is that the SD channels look TERRIBLE on method 1, whereas they look quite good with method 2. One looks real fuzzy, almost as if lower resolution. Like a really bad YT video. The other looks comparable to DVD quality, slightly less.

Realistically, I only have (and only want) one TWC digital box in my house, and that is in the basement HT room. For this other TV (family room) I was hoping to just connect to the wall. But the SD content looks so bad, this is not going to be acceptable.

Anyone have an explanation as to why SD channels can look so differently between the 2 methods?

Since you provide little about your cable system or STB, I'll answer based up the TWC in my area (and my received Cox Cable.)

More and more cable systems are using STBs that only have digital tuners, but still offer analog tiers of programming to their customers. So, they send the analog tier from their headend both as 6MHz-wide NTSC analog signals, and as QAM modulated ATSC digital signals. When you plug directly into your TV, you are watching the NTSC analog signals. Since they come from the headend as analog NTSC, they are susceptible to video noise and all of analog video's other maladies. The STB, however, has no analog tuner. It tunes a signal that came from the headend as a QAM digital signal, and doesn't suffer from the video noise, etc., as does the analog signal. Thus, the signal from the STB appears sharper, because it is. In a nutshell, that's the reason.
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post #7 of 13 Old 06-14-2012, 03:01 PM - Thread Starter
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Wow, extremely helpful reply!

Here is what I found out after further researching, combined with the information you supplied: Some of the SD channels I am receiving directly from 'the wall' and into my TV, are interpreted by the TV's tuner as Standard Definition Digital QAM ATSC, while other channels are seen as Standard Definition Analog NTSC. So I was wrong in assuming that all SD channels where analog signal, in my previous response. I think form what I can tell, the Analog NTSC ones look worse on the TV compared to the digital SD. Now, when viewed from via the STB, all SD channels look good to me, I assume because they are all received as Digital QAM. (cant confirm this, have not figured out how to determine that via the STB).

Now I don't understand WHY the TV itself is able to receive/tune only some SD Digital QAM channels, while tuning other SD channels in Analog. Why doesn't it do the same as the STB, (Tune all SD in digital QAM format) if clearly the TV has the capability of tuning QAM signals?

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Originally Posted by domino92024 View Post

Since you provide little about your cable system or STB, I'll answer based up the TWC in my area (and my received Cox Cable.)
More and more cable systems are using STBs that only have digital tuners, but still offer analog tiers of programming to their customers. So, they send the analog tier from their headend both as 6MHz-wide NTSC analog signals, and as QAM modulated ATSC digital signals. When you plug directly into your TV, you are watching the NTSC analog signals. Since they come from the headend as analog NTSC, they are susceptible to video noise and all of analog video's other maladies. The STB, however, has no analog tuner. It tunes a signal that came from the headend as a QAM digital signal, and doesn't suffer from the video noise, etc., as does the analog signal. Thus, the signal from the STB appears sharper, because it is. In a nutshell, that's the reason.

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post #8 of 13 Old 06-14-2012, 09:59 PM
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Originally Posted by gnolivos View Post

Wow, extremely helpful reply!

Here is what I found out after further researching, combined with the information you supplied: Some of the SD channels I am receiving directly from 'the wall' and into my TV, are interpreted by the TV's tuner as Standard Definition Digital QAM ATSC, while other channels are seen as Standard Definition Analog NTSC. So I was wrong in assuming that all SD channels where analog signal, in my previous response. I think form what I can tell, the Analog NTSC ones look worse on the TV compared to the digital SD. Now, when viewed from via the STB, all SD channels look good to me, I assume because they are all received as Digital QAM. (cant confirm this, have not figured out how to determine that via the STB).

The frequency of a received channel, and whether it is analog or digital, is reported in the STB diagnostic pages. Or, you can just give the model number of the STB. If it only has a digital tuner, it is only tuning digital channels.
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Now I don't understand WHY the TV itself is able to receive/tune only some SD Digital QAM channels, while tuning other SD channels in Analog. Why doesn't it do the same as the STB, (Tune all SD in digital QAM format) if clearly the TV has the capability of tuning QAM signals?

The ones you can receive on your TV are Clear QAM (unencrypted) signals. The other digital channels are encrypted (conditional access.)
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post #9 of 13 Old 06-15-2012, 04:16 AM - Thread Starter
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OK, so possibly what is going on is : the TV is able to 'see' both Digital and Analog signals for a given channel (example ESPN), but when the digital signal is encrypted, it chooses the Analog instead. (when Digital is not encrypted, it chooses that over analog). Whereas the STB can decrypt all digital channels, and chooses the digital encrypted over the analog ones all the time, when available.

Correct?

The STB is provided by TWC, it is a Samsung model SMT-H2360.

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post #10 of 13 Old 06-15-2012, 08:54 AM
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You said the cable box is connected to your TV over HDMI. This means that you have an HD cable box. Are you sure you aren't comparing HD channels from the cable box to SD channels on the TV? I think some cable boxes now automatically tune to the HD version of a channel if one is available.

Also your cable box is most likely upscaling the SD channels and outputting them as 720p or 1080i depending on it's settings. It is possible that you cable box just has a better upscaler than your TV (that seems unlikely though).

Have you checked to see what resolution your TV is reporting when you are using the cable box to watch a channel?
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post #11 of 13 Old 06-15-2012, 02:03 PM
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Originally Posted by gnolivos View Post

OK, so possibly what is going on is : the TV is able to 'see' both Digital and Analog signals for a given channel (example ESPN), but when the digital signal is encrypted, it chooses the Analog instead. (when Digital is not encrypted, it chooses that over analog). Whereas the STB can decrypt all digital channels, and chooses the digital encrypted over the analog ones all the time, when available.

Correct?

Close enough. The STB can decrypt all digital channels for which it is authorized. Plus, there is the matter of PSIP data, which is a topic you should Google or go to Wikipedia.
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The STB is provided by TWC, it is a Samsung model SMT-H2360.

Hmm...are you sure of that make/model number? It's not on my list.
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post #12 of 13 Old 06-15-2012, 07:59 PM - Thread Starter
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SMT-H3260. it was a typo!
(EDIT: Corrected model name again, N for M)
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Originally Posted by domino92024 View Post

Hmm...are you sure of that make/model number? It's not on my list.

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post #13 of 13 Old 06-15-2012, 10:25 PM
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Originally Posted by gnolivos View Post

SNT-H3260. it was a typo!
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Originally Posted by domino92024 View Post

Hmm...are you sure of that make/model number? It's not on my list.

Actually, it's SMT-H3260. I was able to find it anyway. Just a digital tuner.
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