Annoying "mosaic" in digital-to-analog TV conversion

[kx250rider]

Here where I live, we're forced to use CATV since we don't get any air signal; not even radio or satellite. The walls of the canyon are too steep to get line of sight to any DSS satellites. Our cable company, Comcast, is changing over to digital and we got a Motorola digital receiver (free).

When I watch anything on a new digital channel, I see a mosaic breakup of the picture for a split second each time the scene changes. I mean the same as how they distort the face of a child or a license plate sometimes on the news. Also, the sound track is off-sync with the picture by a slight amount. I'm not sure if this problem is an anomaly of watching digital TV through a converter box on an analog set, but it's really annoying! Annoying enough that I shut it off.

I sure hope this isn't how we will all be watching TV on our analog sets in a few years! Any opinions welcome...

Charles

[Chad Hauris]

I would call the cable co. it sounds like there is a weak signal or interference causing errors to be introduced into the digital signal. I have occasionally seen this on DirectTV reception but rarely. I don't think its an inherent flaw in digital TV but that there is some problem with the cable signal.

[kx250rider]

Chad,

That sounds encouraging... I'll put in a complaint and see what happens.

Charles

[RetroHacker]

About a year ago, we got digital cable, and we had it for about a month. It did this, and rather a lot - and some channels were worse than others. There were some channels that were almost entirely unwatchable. The cable company was out here a couple times, and wasn't able to get it cleared up. We're in a new neighborhood, in a new house, so it's not like they're going through outdated or old cable TV wiring. The digital reciever box was a nightmare and was slow changing channels. You'd press the button and a second or two later, the channel would change. The picture was a lot worse than the analog cable (while with the digital box, we still had analog service too). It was bad enough that we had a switchbox set up, so we could switch the set over to analog to watch most things, and only use the digital when it was necessary (some channels were only available on digital). We dumped digital TV a couple months later. It was such crap.

When they actually get this garbage to work, I'll think about it, but until then, I'm keeping my analog cable.

-Ian

[rca2000]

Yesterday, I had the "privlige" of going out to a new plasma instalation, to see why "things weren't right" with this guys tv set.

The problems were" the volume wouldn't adjust, the picture was in the "window" mode"(white bars on each side) and the picture, even in HD mode, looked like SHIT!!

I fond that the cable company had hooked up the audio out. from the box to the audio OUT of the set-- all that got through was a bit of "bleed" and so, that was why the sound was wrong. BUT-- the box must had been wrong, because I could NOT get the "window mode" problem cleared up, when I changed the aspect ratio on the set, it would shift the image to the right. It did NOT do this on a DVD, so the set was not the problem(I checked). It must be the cable box.

BUT-- on the HD channelss he has, (and is paying extra for) the picture quality is NOT much, if ANY better, than normal digital cable, which is only so-so, when the picture is NOT in pixelation mode(which happens too often. ) There was a noticeable grainess, from about 3 feet from the set, and it did NOT liook like the resolustion was any better, though the plasma said it was in the 1080I mode. SO, I tried to explain to the dissatisfied man, that" many of the super-duper pictures you may had seen, of this knockout, breath-taking picture in HD, in stores were SPECIALLY PREPARED, from a stream or a dvd, and that cable, even in HD mode, will NOT look anywhere near as good as those demos, at least around here, on Warner cable. He was not amused, but what else could I do? His is NOT the only set I have seen those "great" (as in pi$$ poor) HD images from, either.

IMHO, Digital and HD is a HUGE rip-off, and a LOT of people are paying extra money, for ... little of NO improvement in picture quality!!

[Eric H]

Man do I get tired of hearing how crappy HD is, personally I'm thrilled with it!

I can't say about Cable since I don't have it but HD from Satellite looks great, (Charles, I realize you have no choice and that's a bummer!) it suffers only from the occasional breakup or blackout but it's minor and no more annoying than the static, ghosts and other anomalies that analog has.

[andy]

The problem is that the cable compaines recompress the digital HD signal to save bandwidth. Even if they're keeping the full 1920x1080 resolution, they recompress it at a lower bit rate than what you get over the air. Recompressing MPEG is a bad idea and introuduces more artifacts. Cutting the bit rate makes this bad situation even worse. It's like converting a 160 kbit MP3 to a CD and then back to a 128 kbit MP3. The result is worse than if you had gone straight from an original CD to a 128 kbit MP3.

[3Guncolor]

I have a few questions for Charles,
What type of Motorola box did you get?
I take it he was using a NTSC set
What channels were you watching?
I don't want to get into the analog vs digital but good analog is better then low bit rate MPEG2.
Most data rates below 3megs per sec per channel will produce some of the problems Charles has reported.
Steve

[3Guncolor]

Andy,
Not all cable systems recompress their channels. I know this to be a fact.
There are always bad apples but there are systems that do care about their product and want it look good we do want to keep customers.
Steve

[kx250rider]

Steve,

The Motorola box is a DCT-2422 (with a long suffix of 10 or 12 numbers & letters). Photo below....

I don't have any tech details on the system we're on, but I will say that the problem I'm complaining about is ONLY on the digital channels. The analog channels received through the box are fine. But I also share Ian's problem with the D.E..L...A....Y.....S on switching channels!!!! Forgot to mention that. It's kind of like a Chevy truck I bought in the late 90s with an automatic transmission... You'd put it in reverse, wait, then BANG! into reverse. This was "normal" as I found when I demanded to test drive others.

The symptom of the "mosaic" flashing is also showing up when an object moves fast across the screen. I forgot to mention that earlier.

Eric H,

I agree with you on the DSS digital... I had that once before when we lived in Chatsworth. It was great; none of these problems unless there was a storm.

Charles

[Chad Hauris]

The delay on switching channels is in directTV too, it seems to take time to lock on to the channel. Usually I don't just click the channel key, I go to the guide screen to view what's available and then activate the desired channel so the delay doesn't bother me.

If you are getting true HD TV you really can tell the resolution difference and it is a lot better. Have seen HD from an antenna and from DIrectTV satellite and it really does look good, not so much to make me want to pay thousands for the TV set and new satellite receiver though! I get just as much TV enjoyment from the 23" Zenith ChromacolorII as from HDTV.

[andy]

The picture shouldn't block up, but you will see MPEG artifacts. Every digital cable system I've seen massively overcompresses the channels. Any fast motion will block up like something you downloaded from the internet.

The delay is normal and is a result of MPEG decoding. MPEG works by not sending every frame as a complete image. It only sends the difference between frames most of the time with an occasional complete frame. The box has to wait for one of those complete frames before it can display a picture.

That's an old box, so the computer that runs it is also slow and will make the menus sluggish. You might ask about getting a HD box. Many cable companies don't charge extra for a HD box. A HD box will work with an NTSC TV and the menus are much faster. Even HD channels look better on an NTSC TV because there are fewer noticeable compression artifacts. The component and S-video outputs also improve the picture.

[3Guncolor]

Charles,
It is true that all digital services have some lag when changing channels it does take some time for the “box” to do it’s thing. If you are not using HD TV I would not recommended getting a HD box they seem to have more issues with the standard channels. While that box is not the latest and greatest Motorola box it should have the same picture output.

I will use one channel let’s say “the Disney channel” we receive that channel from Disney using their digital feed we take the their digital output combine it with other channels and send it out. We do not add any compression to it. At my system we try to keep the channel loading under 100% at all times so there is almost never any “rate shaping”.

This would be the same signal the dish people would use. Most of the programmers are using digital satellite feeds now so we try to use their digital feeds if possible. Again I can’t speak for all cable companies and I don’t work for Comcast.

It always bothers me when the cable people always seem to get the blame when at times we are sent poor video or over compressed digital signals to begin with.

I have a Zenith 1977 cromacolor II set that I bought new from the store I worked at as a kid, it has very low hours and works great. I have it hooked up to a Motorola DCT2500 and now most of the channels are digital and it is the best picture I have even seen on that set. We are in the process of simulcasting our analog channels too. But at this time customers can still use the old analog channels if the wish by not using a box and going cable direct to the set.
Steve

[andy]

It's nice to hear of a cable company that cares about quality. This is far from typical.

Rant warning------

My town has Adelphia and the general rule is that if there's a picture, it's good enough. If there's a problem, it's always the customers fault. It took 2 months for me to get semi reliable internet. They blamed my cable modem, computer, splitters and house wiring. In the end it was the underground line from the box to the house. Quess what they did to fix it? They swapped my line for my neighbor's line. This was 4 years ago and they still haven't bothered to run a new line for my neighbor. I still have flaky internet service, but it's usable most of the time.

[Eric H]

FWIW the Standard Definition on Satellite is pretty bad!

It's very compressed and soft looking, not to bad on a 27" set but very noticeable on a big screen.
The tradeoff is that there's no interference and the picture is at least clear.

The best thing about Sat TV is the reliability, I can only recall one time in the last 5 or 6 years that it went out.
Now if the Martians ever shoot down the satellites we might be in trouble