Joe Schmoe

I have 2 HDTVs (1 32" 720p and 1 73" 1080p), and I have both connected to indoor antennas. The 32" is connected to Tivo, and the 73" is connected to an Onkyo receiver that is supposed to output everything in 1080p.

No matter which TV I watch CBS HD on, I see LOTS of pixelation during fast movment. At first I thought the pixelation was because CBS broadcasts in 1080i (instead of 720p), but NBC airs in 1080i too and I don't see any/much pixelation on NBC. (I don't see any/much pixelation on FOX or ABC either.) It's very annoying. Any ideas as to why the pixelation is worse on CBS?

Jay G.

1080i and 720p have the exact same amount of pixels/sec in ATSC. 720p is approx 1 million pixels every 60th of a second. 1080i is about 2 million pixels, but only half (approx 1 million) is shown every 60th of a second.

If you see pixelation issues, it's either in their encoding (to MPEG2), or possibly a reception issue.

Joe Schmoe

So if one network looks ok but another one doesn't and they both air in 1080i, would that make you lean toward encoding issues?

Solid Snake

why is this on the HD forum? I can SEE how it can seen as an HD issue but...it's not HD media.

BuckNaked2k

Yes, it is.

Alan Smithee

It depends on the local station too- especially if they have any "subchannels" with other (usually standard-def) programming on them, that takes bandwidth away from the main HD channel. Even stations in my area that don't have them often have a noticeable amount of compression artifacts, but there's a ton of other reasons why I don't watch TV anyways. Blu-Ray (and HD-DVDs) look great, and that's all that matters.

The FCC should have required minimum bitrates so pixelization didn't occur, but they're obviously more concerned with people saying naughty words.

Kevin M. Dean

From the top of the HD Talk page:

"HD Talk The place to discuss HD DVD, Blu-ray and all other forms and formats of HD and HDTV."

obidawsn

It's definitely either the encode or how it's being transmitted from your local station. Our local CBS affiliate has CW on their second channel, and there was one time they tried to do HD on both channels. The encode was horrible and everytime there was any fast movement on the CW (not sure about CBS as I don't watch anything on that network) the picture would break up tremendously. Not fun when you're watching Smallville and an action scene would come on. Needless to say, that didn't last long. The station I work for refused to have another channel for a long while as they wanted to use as much bandwidth as possible for their main channel, but money got the best of them I guess as they now have a second channel. I see pixelation on a lot of channels, though, but I think it's our cable company. Though it's weird that at one time we couldn't get Nick Jr. and our local PBS station in HD would break up every few seconds. I knew it had to be the cable as the PBS station's SD was fine and it should be the same signal. I was about to call the cable company about it, but we decided to move and everything works fine. Must have been the cable infrastructure at the apartment building where we lived.

One thing I would check is to see if your CBS affiliate has other channels on their signal. As other people have mentioned, that could be the problem. Funny thing, though, is our PBS affiliate has several channels (up to 5 at times, I believe) and no issues at all. Though they don't always have all 5 channels as some of them only show programming at certain times (I believe there are 2 of them that are the state version of C-span showing the state House and Senate) and at times they turn their main channel from HD to SD when they aren't showing HD programming to give more bandwidth to other channels. Their setup is pretty interesting and last I heard, our engineers have no idea how they're doing it. But they have a complex way of using their bandwidth and it looks like a good encoder for the HD channel.

milo bloom

Would you mind sharing your general location? There might be other folks that have noticed this in your area.

Solid Snake

well shit me in a box...I never went past Blu-Ray...lol

milo bloom

There is precedent for allowing tangent discussions. I recall years ago a mod had to come into the main DVD section and say it was okay to talk about LD and VHS collecting also.


And here in Chicago, the CBS station does seem a little iffy at times. Our first HD "device" was one of those crappy converter boxes on an older (but HD ready TV) and we couldn't get CBS for crap. After buying a new Samsung LCD last summer with a built-in tuner, it comes in great.

Not that we watch CBS, but, it's there

Alan Smithee

CBS = Can't Be Seen
CW = Can't Watch

Joe Schmoe

Boise, Idaho.

Joe Schmoe

This year the local CBS affiliate added one subchannel that's not HD. However, I noticed the pixelation before they added the subchannel.

naitram

Ah, that explains it. /thread closed

lizard

My guess would be a reception issue unless the measured signal strength is consistently high. Different frequencies, weather issues, the direction the antenna is pointing, and the distance from the transmitter can account for differing reception quality between stations. For me, the direction of my antenna is the biggest factor in whether or not I can receive a digital station well or at all.

You can find out the direction and distance of transmitters from your address at TVfool.com.

jjcool

I immediately thought "reception issue" as well. Are HD signals affected the way the old broadcast signals were with regards to which direction the antenna is pointing?

Anubis2005X

I dunno, but ABC HD doesn't look nearly as sharp to me as the other stations on Verizon FIOS. Don't know what the deal is...

milo bloom

I have my antenna in my attic, and I actually have it cocked a few degrees "off" the cardinal compass point to point it more directly towards downtown Chicago and it seems to be a little better.

lizard

In my experience digital OTA signals are very sensitive to antenna positioning. If I shift my antenna 90º to 180º away from the transmitter I get zip: no measurable signal at all. That's for UHF frequencies and a large rooftop style antenna (although mine is in a tree). Analog VHF signals were much more forgiving, although the picture was often poor. I do find that I can pull in a signal with the antenna 30º off-line with the transmitter if the signal is strong.

Distance matters a lot because the signal strength can be expected to decline by the square of the distance. The reason I mention this is because it is possible that the OP's CBS station is farther away or in a different direction from the other stations that come in without pixelating. Using indoor antennas requires a strong signal from a close or powerful transmitter. But I'm just guessing of course.


BTW, the "channel" of a digital signal is often quite different from the frequency used to broadcast it; digital channels are arbitrarily assigned. Again, I recommend TVfool.com for details about individual transmitters.

Alan Smithee

Compression artifacts don't vary based on signal strength- your tuner either 'sees' the signal or it doesn't. The only glitches you get are things like dropouts and picture freezing (I'm amused by stuff like the signal cutting out for a second, then you get a person in the next shot who's outlined by stuff from the previous shot.)

Joe Schmoe

The NBC and CBS stations are in Boise. I'm about 25-30 miles away from both stations, so I'm not sure why NBC would always look good and CBS always has pixelation during fast scenes. When there's no fast movement, CBS looks fine.

ABC is much closer to me (maybe 10 miles) than the other two and looks great most of the time. However, last night I noticed white specks during their HD broadcast (kind of looked like old fashioned static). It was very obvious in dark areas of the picture. I didn't think that kind of interference was possible with a digital signal. The other annoying thing my ABC station does all the time is when a show comes back from commercial the show begins in SD and then suddenly switches to HD. Sometimes the switch happens right after the commercial break, but other times it can take 10 minutes before it switches back to HD. What's up with that?

kefrank

+1

The symptoms of a reception issue are much more disruptive than the "pixelation" that the OP is referring to. This is almost certainly just a compression or local transmission thing.

On the reception note though, in my experience, getting a reliable OTA signal is pretty much black magic. You can be too far from the towers, but you can also be too close or in an area that is more subject to multi-path interference. Ultimately, that's one of the main things that drove me to Dish.

kefrank

Movement is much more challenging to compress than a static image. Fast movement generally always exposes compression artifacts more obviously than static images do.

obidawsn

Yeah, Analog signals were a lot more forgiving as Alan sort-of explained. Analog signals can be weak, but you still get the picture, though the picture may fade or go staticy. Digital signals are made up of 1's and 0's just like anything else digital. It's either there or not. You may get some pixelation in a weak signal, as some of the 1's and 0's get lost, but it's usually pretty major pixelation. It looks a little different than what the OP is talking about. I know we had that problem when we switched our live shots from analog to digital (thanks to the government selling the signals to Sprint and forcing us to change). We used to have live shots that would fade if the signal dropped, so we could still use it or know to get out of it. But with digital, you usually just go to black. Sometimes you get that digital break-up before, but not always. Gets frustrating as a director.


That's probably because their master control switcher isn't in HD. A station can show HD broadcasts from other sources, but not have their main master control in HD. We did that for a while as we can just send the network HD feed directly out bypassing the switcher (which was SD). When they go to commercial break, they have to go through the master control switcher, so the bypass gets switched back to the main switcher. When the operator goes back to network, they probably go to network on the main switcher (which would be in SD, even if it's downscaled from the HD signal) then switch the bypass to the HD signal. The various times it takes for that is probably how well the operator is paying attention to what he's doing. Our ABC affiliate was probably the last to go HD and they did that a lot. And anytime there was a weather alert where there was a crawl or weather "bug" in the corner, they had to go through the main switcher, so it was always in SD. Bugged me trying to watch Lost and having to watch the SD version. One way to see if that's the case with your station is to see if their local news is in HD or SD. If their master control switcher isn't in HD, their local news probably isn't either. And more than likely all their other programming as well (other than network).