Wikipedia:Reference desk/Archives/Miscellaneous/2014 August 26

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August 26

Are digital TV pictures broadcasted as one image?

I am watching TV on a new 1080p LED LCD TV with a coaxial cable plugged into the wall in USA. The building provides free cable TV, so I don't need a cable box or anything. I recently added a 90 degree coaxial elbow joint connector so that I didn't have to bend the coaxial cable because it was behind a media cabinet.

I'm not sure if I'm seeing some signal degradation or whether it's placebo. When watching a news channel, such as CNN, I noticed that the vector words such as the station logo or the headings are equally sharp. But I'm not sure if the reporters' faces are more blurred.

So my question is, are all the element of news channel (the logo, the title of the story underneath the picture, and the actual video image) broadcasted as one component? In other words, if the words are equally sharp pre and post adding the 90 degree joint, does that mean any perceived reduction in video quality is just placebo? Thanks. Acceptable (talk) 05:16, 26 August 2014 (UTC)

It's all one image (except for closed captioning). If it's analog cable, I suppose signal degradation could have a more noticeable effect on faces than on crisp shapes, though I'm not sure exactly how. If it's digital cable, signal degradation would show up as blockiness/stuttering, not blurring. -- BenRG (talk) 06:10, 26 August 2014 (UTC)

Thanks. Would it make a difference in terms of blockiness/stuttering reduction if I used a 15ft instead of my current 25ft coaxial cable? I am using it for indoors with DirectTV I believe. Acceptable (talk) 06:38, 26 August 2014 (UTC)

The difference in loss between the two cable lengths is so small that you will see no difference unless something is wrong with one of the cables or its connectors. 84.209.89.214 (talk) 15:50, 26 August 2014 (UTC)

You seem to be misusing the term "placebo". Also note that some display technologies can display a sharper image in some colors or screen regions, either of which may favor captions. This is true of CRTs, not sure of LCDs. Also note that 1080i images are "interlacedspersed", meaning they display every other line, then go back to fill in the missing lines. So, rapidly moving objects can look blurry, since you get 2 different, overlapping images. If the captions don't move, they should look clear. StuRat (talk)

The "i" in 1080i stands for Interlaced video. 84.209.89.214 (talk) 19:02, 27 August 2014 (UTC)

Thanks. StuRat (talk) 23:56, 29 August 2014 (UTC)

Digital video is not sent a picture at a time. They ensure the whole picture is refreshed every so often and in between they apply differences - which may include bits which move at a constant rate for instance. This is to cut down the amount of information that has to be transmitted. You might notice with bad reception the picture sometimes goes blocky or stops changing for a moment, this is because changes have been corrupted. Also the logo of a channel will be applied on top of an original video at the station and then an integrated video sent out.. If there are problems with the original video they will be reproduced but the logo will still be okay. Dmcq (talk) 14:32, 27 August 2014 (UTC)

Thanks for the responses. Either way, it would be a better idea to use a 90 degree elbow joint rather than trying to bend my coaxial cable to a very short radius 90 degree turn right? From my understanding, the latter will damage the cable over time? Acceptable (talk) 18:55, 27 August 2014 (UTC)

It depends what "very short" means. If the cable is actually kinked - if it's no longer circular in cross-section - then the signal will be degraded. This isn't damage "over time", it's immediate damage during the installation. However, a tight bend that doesn't distort the geometry is probably no worse than the loss introduced by an extra joint (especially if you use the ultra-cheap "twist-on" F type connectors). I'm assuming that once the cable is in place, you don't intend to move it about. Tevildo (talk) 23:43, 28 August 2014 (UTC)

However, there could also be damage over time, since there's a concentration of forces there. Thus vibrations will cause the metal to fail there. StuRat (talk) 23:54, 29 August 2014 (UTC)

Well, assuming the OP is using standard RG-6 cable, the plastic insulator will be damaged by excessive bending long before there's any significant strain on the centre conductor, and vibration shouldn't be an issue in a domestic installation. I would still recommend against using an unnecessary joint in the cable. Tevildo (talk) 00:22, 30 August 2014 (UTC)

There are all sorts of vibrations in a household. There can be trucks driving by outside, dishwashers running, people walking around, the bass from the TV, etc. I would expect the insulation to fail, too. I just tossed out a PC keyboard that had the wire fail in a very similar way, along with the insulation. StuRat (talk) 04:32, 31 August 2014 (UTC)