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Discussion Starter · #1 ·
As a complete newbie (only a few days with my HDTV receiver) I am VERY disturbed by some things I'm seeing with HDTV.


The much-lauded PBS demo is flat out STUNNING, that is unless it's displaying moving water, blowing leaves, etc.


The 76ers in HDTV (1080i) looked absolutely fabulous until the action started and then it was pixelation hell.


A nature show on PBS involving large cats (I don't recall if they were tigers, lions, jags, etc.) and lots of shots in the woods was virtually UNWATCHABLE due to all the artifacts.


What gives? From the newbie side of things NONE of this has been mentioned to us. We're all thinking HDTV is just as stable as regular TV with better resolution. Instead what I'm seeing is a bunch of bad artifacting. When those aren't there, as I said, it is often stunning but that illusion is quickly destroyed by the artifacts. Friends who saw the 76ers with me, as I'm the first of my friends to get HDTV went away saying, "Thank GOD I didn't spend money on THAT!"


Confused.... I'm assuming this is some sort of badwidth issue but I don't see why. The whole point of HDTV was to improve the quality. Not just tempt you with what it almost can do. Have I spent thousands of dollars and much headache for a technology that isn't ready for primetime?
 

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Some people are sensitive to the artifacts, and some aren't. Degredation of your typical analog signal results in blurriness, ghosting, and wavy lines. Pixelation, blocks, jaggies.... welcome to the 'digital degradation' of the 21st century!


Unfortunately I'm extremely sensitive to digital artifacts, having come from a video-oriented background. My parents have digital cable, and the picture drives me up a wall.


- Chris
 

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Sounds like a local station issue. Are you sure the stations you're watching aren't running any subchannels along with the HD feed? Your experience is not typical.
 

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Agrajag:


What you are describing is often the symptom of digital stations that are only getting "borderline" reception. Can you tell how your signal strength is on these channels you are describing?


First, you failed to mention exactly how you are receiving these local channels. Is it from an antenna, or from a Cable TV company's high definition package?


With analog channels, if the signal approached borderline reception, we always saw ghosting, snow, etc.


With digital, a lot of people claim reception is "all or nothing." In other words, you either see it, or you do not. However, I have found this is not 100% accurate.

In my experience, there are three types of reception: 1.) Rock solid... you might occasionally see a tiny bit of pixelliztion, but this is usually only when there are "hiccups" from outside interference such as weather, airliner interference, etc.

2.) Borderline... frustrating, because now you do see LOTS of pixellization, and also often experience audio dropouts and even complete video dropouts. You never see ghosting, or audio noise, or snow, or similar artifacts. But, the picture is "in and out," and it often breaks up digitally or "pixellates" when the antenna continually loses the signal.

3.) A black screen. The signal is there, but too weak for you to get a lock. Since it is not there, you get nothing.



Under normal circumstances, I may see pixellization perhaps once every week, or maybe twice a week. My signal strengths are all strong, I am viewing on a 65" Mits sitting 10 feet from the screen. I do not believe it is simply a case of not noticing -- I tend to be very picky of any degradation of image quality, including pixellization.


I could be wrong, and maybe you are just much more sensitive to this issue than I am. However, what you are describing is similar to what I saw when I was using an inadequate antenna, (indoor set top). Then, I saw LOTS of pixellization as the picture broke up constantly, and I also had a lot of dropouts. Once I upgraded to an adequate antenna for my location (outdoors, on the roof, a fairly large multi-directional), all of these issues basically disappeared.


Just some thoughts... If I am way off base, obviously, ignore this.


-Bruce in Chi-Town
 

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Discussion Starter · #5 ·
Quote:
Originally posted by vruiz
Sounds like a local station issue. Are you sure the stations you're watching aren't running any subchannels along with the HD feed? Your experience is not typical.
How can I tell? This is WHYY in Philadelphia for the PBS demo and Comcast SportsNet for the 76ers problem.


As far as being sensitive to them, you'd have to be BLIND to not see them on that nature show. I could have taken a snapshot and shown it to anyone and defy them to even tell me a living creature was in the picture let alone being able to see it as a tiger. The entire picture was made of of maybe 64 artifact blocks.


With respect to signal strength, this is all coming in via Comcast's HDTV receiver. I don't have much control over that. I'd consider an HDTV antenna but I'm a big Tivo fan so I'm not getting an OTA receiver until the DirecTV HD-Tivo is available. I can't see wasting several hundred dollars for a receiver that will only get a few channels and then not be able to record them, time shift them, etc.


I have been a DirecTV customer since 1994 so I'm VERY familiar (too familiar) with digital artifacts and getting near the borderline. This doesn't seem to be it as it's entirely predictable with respect to complexity of the image being displayed. If water is rough, it will be a mess. If water is calm, it will look fantastic. If players don't move, it's great. If they start bouncing around, it goes to hell.


And I am getting audio dropouts. They are brief but they happen often on nearly all the HDTV channels Comcast is providing. (ABC, NBC, PBS, HBO and Comcast right now).


No black screens yet.
 

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Sounds like you have a signal problem.


If you have a marginal signal, then static pictures (low bitrate) look ok. Moving pictures which involve a higher bitrate look bad.


If this is OTA then get a bigger antenna.


If this is SAT or CABLE then work with your carrier.
 

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> The entire picture was made of of maybe 64 artifact blocks.


I have never, ever seen artifacting that bad on any HD channel. The worst artifacting I have seen is certainly noticeable, but not anywhere near as obtrusive as what you're describing.


> With respect to signal strength, this is all coming in via Comcast's HDTV receiver. I don't have much control over that.


It could be that Comcast is overcompressing the HD signals that they send out to their subscribers, but were that the case I would expect multiple long threads dedicated to complaining about it, so I presume that isn't the case.


That leads to the possibility that the Comcast supplied box is defective, or for some reason the signal strength coming into your home is inadequate. Probably your best bet is to contact Comcast and let them know that either your box or hookup is defective, and have them replace the box or fix your hookup.
 

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Sounds like an issue specific to your particular Comcast cable network, as most Comcast subscribers are not seeing such things, certainly not to the extent that you are...I would call and complain.


I would also call the local PBS affiliate and complain about their PBS loop. Tell them the signal you are seeing on Comcast is so pixelated so as to be unwatchable. Perhaps they can work something out.
 

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I agree with bhummel2001 thoughts, but want to add my own. I 've been in the RF and installation industry for over 10 years now. What you are describing is almost 100% a signal issue. This is mostly due to bad rf connectors where the shielding is poorly connected to the connector resulting in an unbalanced signal to ground causing a lower signal to noise ratio (i.e. higher noise floor). This in turn lowers the bandwidth posible to transmit the digital signal to the tuner. I have only seen a few minimal cases (for cable) where the problem was outside the house. It's almost always due to poor connections throughout the home that causes the dropouts. Other than the aforementioned rf connectors, lower frequency taps and splitters produce horrendous signal problems. For replacement in cable, use 1Ghz splitters, in Sat systems, use 2Ghz components. Also the use of different sized coax on components cause problems as a splitter connector becomes "opened up" and not making a good connection.

I've had numerous discussions with homeowners who claim ther cables are perfect. I would merely take a 100ft or so piece of cable off a spool, put GOOD crimps on each end and run it from the source at the street or from the sat dish to the tuner provided. In each case, I was able to get the homeowner to see the error of their ways and they gladly paid me to rerun their coax throughout the home.


vegggas
 

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Quote:
Originally posted by Agrajag
As far as being sensitive to them, you'd have to be BLIND to not see them on that nature show. I could have taken a snapshot and shown it to anyone and defy them to even tell me a living creature was in the picture let alone being able to see it as a tiger. The entire picture was made of of maybe 64 artifact blocks.
You need to call Comcast and let them sort out the problem. Sounds like a bad STB.
 

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Discussion Starter · #11 ·
Well, let's hope it's a bad box though it could be a bad cable feed. The cable comes into the house, goes almost immediately to a wall plate where it then is hooked to the back of a wall plate via a small gold connecter and then then another cable goes from the wall plate directly to the box. I haven't yet seen where they've split it as it is split since I have a cable modem (which runs GREAT with no drop-off at all) and cable on the second floor.


Either way we'll get them on it.


I am VERY relieved (for now) to find out that this isn't the norm for HDTV. Thus, the picture should just stabilize from here.


That said, couldn't the cable company test the signal strength on the line itself going into the box and determine if that's the cause? If that looks strong then it IS the box.
 

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Quote:
Originally posted by Agrajag
A nature show on PBS involving large cats (I don't recall if they were tigers, lions, jags, etc.) and lots of shots in the woods was virtually UNWATCHABLE due to all the artifacts.


What gives?
First of all, it was in SD, not HDTV.
 

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Discussion Starter · #13 ·
Fine, the nature show may have been in SD but it was listed in their HD grid so that was my mistake. It was just widescreen SD apparently and this still doesn't help with regard to their HD demo feed or the 1080i live games that were NOT in SD.
 

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Well, the advice about calling Comcast should help. What you are experiencing is not normal, and is NOT a flaw with HD. There likely is a problem with your STB or your cables.
 

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While I certainly do not have this problem, some of what he is describing can also to some degree be 1080i motion artifacts. However, unless you are very close to the screen, you should not be able to see these. I do not see them at my sitting position 9 feet from the screen. I am using a 42" plasma. The same is true with my 34" direct view as well.
 

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One question: How close are you sitting to your HD display? The scenes you described -- running water and blowing leaves -- are among the hardest scenes to encode because of the almost random motion of similar-looking images. (Somehow I think you already knew that.)


HD was intended to be viewed at a distance equal to or greater than three times the picture display height. Compressing HD to 19 Mbits per second requires that you throw away A LOT of data. The intent was that any artifacts caused by this compression would be lost due to lack of visual acuity at that viewing distance or greater.


If you put your face close to a broadcast HD display you will see artifacts on some images. They are just not supposed to be visible at a distance from the screen. (Assuming your system is working well to begin with.) Signal strength should not be an issue. A busted decoder definitely will be an issue.


Also, a note to the KPHO viewers: Don't count KPHO out yet. There is some movement on the HD front. Even the 5.1 front. Be patient!
 

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Discussion Starter · #17 ·
Quote:
Originally posted by hphase
One question: How close are you sitting to your HD display? The scenes you described -- running water and blowing leaves -- are among the hardest scenes to encode because of the almost random motion of similar-looking images. (Somehow I think you already knew that.)
I'm 12' from a 58" screen. But trust me, what I'm seeing could be seen from 30' away easily. Motion artifacts are a problem but these are so poor and so frequent that I find it impossible to believe that they're right. As I said, that leopard show was nothing but a mess 30% of the time to the point of not being able to identify ANYTHING on screen. The 76ers game was almost as bad several times.

Quote:
HD was intended to be viewed at a distance equal to or greater than three times the picture display height.
Well, at 12' I'd be JUST under that. The set is just over 4' tall and that includes the base. I suspect they meant the height of the actual display in which case I'm MORE than far enough back.


My wife, who almost never sees DirecTV digital artifacts (and those of you who have DirecTV know how bad they can be) sees these with ease.


Comcast is due here between 2-6pm.
 

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Agrajag, What you described sounds like the perfect argument for 720P instead of 1080i. For really fast moving objects 1080i will have motion artifacts because of the interlacing. You mentioned that when everything is calm then the picture is stunning. If you do a search of 1080i vs 720P on the internet and the forum you can read up why many purists argue for 720P (I myself also see this and actually prefer 720P source to display than 1080i). HDNET on directv has awesome HD programming. However, sometimes they show some fast moving action with alot of fast water and you can clearly see that the cameras have a tough time with it.
 

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Compression artifacts are not specific to 1080i; they have nothing to do with interlace. You get them on overcompressed 720p as well. 720p does require less bandwidth than 1080i, so there may be fewer artifacts in a given [lower] bit rate.


If you try to do 1080i sports in 12Mbps, you are going to get a lot of artifacts, whereas you won't get nearly as many in 720p30 at the same bit rate. If you take an uncompressed HDTV feed, or provide 1080i sufficient bandwidth, you won't get any such artifacts, although you will still get that slight blurring / reduced resolution during fast motion.
 

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Well, I have to admit I've seen everything that he is talking about. Although Comcast Sportsnet HD broadcasts seem to be displaying a lot less of the artifacts than when they first started out. I don't notice any artifacts on the local ABC channel, but I have seen them on them on our NBC affiliate. If his STB is screwed up, mine must be as well. But I find it stange that ABC seems fine, except for those damn green lines that flicker across the screen every now and then.
 
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