Artifacts with HD DVR - AVS Forum
HDTV Technical > Artifacts with HD DVR
maxim0512's Avatar maxim0512 07:33 PM 09-30-2009
I'm an avsforum n00b, so apologies in advance if this is in the wrong forum.

I recently got a 42" Vizio 1080p set and connected a Sony Blu-Ray and a Comcast (greater Boston) HD-DVR, both with HDMI.

Everything from the Blu-Ray comes through flawlessly.

Watching the HD-DVR (a Motorola DCH3416), however, I often get digital artifacts, especially horizontal bands of pixelation. I've tried swapping the HDMI cable, removing my cable splitter, and moving the cable away from power cords and speakers, but none of these had any effect. The HD-DVR is outputting to the TV at 1080i. It seems like *maybe* the artifacts occur a bit more often when the device is recording one show and displaying another (the DCH3416 has two tuners), but I see the artifacts frequently enough (a few times per minute) even when just watching live TV to think it's not just that.

Has anyone else experienced this? Might it be a bad box? Or is it typical of Comcast HD? Any other ideas for troubleshooting?

Thanks!

maxim0512's Avatar maxim0512 07:39 PM 09-30-2009
I should also mention, although I'm not sure it's related, that certain SD content coming in via the DVR (some commercials during HD shows and certain shows from SD channels) displays with a thin flickering horizontal bar across the top. This goes away if I have the TV zoom the image, cutting off the top edge.
demonfoo's Avatar demonfoo 09:27 PM 09-30-2009
Quote:
Originally Posted by maxim0512 View Post

I should also mention, although I'm not sure it's related, that certain SD content coming in via the DVR (some commercials during HD shows and certain shows from SD channels) displays with a thin flickering horizontal bar across the top. This goes away if I have the TV zoom the image, cutting off the top edge.

That's actually NTSC line 21; that's where the closed caption data (and sometimes other bits of data) are passed on analog TV programming. That's normal behavior with analog programming, and even sometimes on certain digital SD channels (though it's not supposed to, it's still done sometimes anyway).

As for the artifacts you mention, it might be a signal problem, or it might be a box problem, or it might be bandwidth starvation on the channel you're watching. Do recordings at different times of the day exhibit it more or less? Do recordings from a specific channel have more notable macroblocking/pixelation?
Mike99's Avatar Mike99 12:13 AM 10-01-2009
My last DCH3416 displayed a few pixels every so often which I never noticed on the previous DVH3416. These were recycled units so who knows what they've been through. I finally got a brand new DCX3400 a few weeks ago & have not noticed the pixelation. Since the new one does not exhibit the same problem I'd have to conclude that on my end the old DVR was the problem, not the signal.
maxim0512's Avatar maxim0512 01:54 PM 10-01-2009
Quote:
Originally Posted by demonfoo View Post

That's actually NTSC line 21; that's where the closed caption data (and sometimes other bits of data) are passed on analog TV programming. That's normal behavior with analog programming, and even sometimes on certain digital SD channels (though it's not supposed to, it's still done sometimes anyway).

That makes sense, thanks!

Quote:
Originally Posted by demonfoo View Post

As for the artifacts you mention, it might be a signal problem, or it might be a box problem, or it might be bandwidth starvation on the channel you're watching. Do recordings at different times of the day exhibit it more or less? Do recordings from a specific channel have more notable macroblocking/pixelation?

I've eliminated the signal as a cause, as the same artifacts do not occur at the same place/time if I rewind and watch the same scene again. So, it's something happening during playback, in the path to the TV, or in the TV itself. Since I've tried a couple HDMI cables and the behavior doesn't occur with Blu-Ray, I'm guessing it's happening during playback.
maxim0512's Avatar maxim0512 01:56 PM 10-01-2009
Quote:
Originally Posted by Mike99 View Post

My last DCH3416 displayed a few pixels every so often which I never noticed on the previous DVH3416. These were recycled units so who knows what they've been through. I finally got a brand new DCX3400 a few weeks ago & have not noticed the pixelation. Since the new one does not exhibit the same problem I'd have to conclude that on my end the old DVR was the problem, not the signal.

Thanks for the info. It does seem likely that it's a problem with the box, though from your experience, it's not clear if it's an inherent problem with the DCH3416 (i.e., fixed only by getting a different type of hardware) or a pair of bad units that you and I each ended up with. Sounds like a visit to the local Comcast office may be in order in either case.
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