Converter box blurring picture?
March 26, 2009 12:45 PM   Subscribe

Is a new TV converter box blurring my digital picture?

My new analog to digital converter box (Channel Master 7000) gives an DVD quality picture to my old analog TV except when the camera pans. At that point the picture gets noticeably fuzzy. For instance, when slowly panning across a brick or stone building, the joint detail disappears and the building facade looks smeared. (Signal is strong and this is not visually similar to the pixelation caused by a weak signal.) If the TV cameraman is walking along following a moving object, the whole picture suddenly degenerates from a finely detailed broadcast image to something akin to a Youtube video or an old VHS tape copied at lowest quality. The Channel Master box has been highly rated for picture quality so I'm wondering if this is a problem endemic to converter boxes, or to digital television or a compression artifact that this brand of box is creating. Have others noticed this problem? Should I switch to a different brand? (TV is Toshiba, using composite video connection)
posted by bbranden1 to Technology (4 answers total)
Fast pans are a problem generally for digitally encoded broadcasts with a fast codec such as MPEG2 (which I believe is standard for US ATSC digital TV), but you shouldn't theoretically see anything worse than an equivalent fast pan on a DVD, which also uses MPEG2 - which by the sounds of it are fine on your TV.

The problem could be either bad encodes by the station broadcasting, or a limitation of the digital-analog converter chip in the Channel Master 7000. Also, composite is a pretty crappy quality standard these days; if your TV supports the svideo available on the CM7000, I'd definitely switch to it, though obviously if your TV doesn't support than then you don't have a choice.

One possible way to isolate the problem would be to compare to TVs using built-in digital decoders, or at least digital inputs like HDMI (but test receiving the same SD channel you are) - if the same broadcasts still looks blurry on pans there, then the problem is the encodes at your provider's end. If they don't suffer from blurring, then it's likely the channel master 7000 at fault. Whether there's another model on the market that does a better job, there I'm afraid I can't offer any advice.

You could test quality on friend's TVs, and you might be able to get a look at broadcast quality TV at a TV shop, instead of just the shop's own advert video or DVD playback.
posted by ArkhanJG at 1:25 PM on March 26, 2009

Does it do this on all channels? In the past, I noticed that sort of quality on certain stations that hadn't yet converted their broadcast facilities to digital. In other words, their digital signal was being encoded off of their old-school analog signal. And the encoder wasn't doing a very good job. But I doubt that's the case now, most stations should have converted over.

More likely is that the converter box is doing a bad job of converting the digital signal from the antenna down to whatever analog output its doing. It's probably messing up the conversion from progressive to interlaced.

It's probably not the TV, that's not something I'd expect a TV to do to a composite signal. (Unless the TV has some kind of error correction mode, you'll have to go through the menus.)
posted by gjc at 4:06 PM on March 26, 2009

Response by poster: It's starting to look like this problem might be limited to one digital PBS station (Oregon Public Broadcasting 28.3) broadcasting at 480i. The picture from this channel also shows what looks to me like very slight compression artifact and a tiny image softness even in static scenes similar to what I've seen in Tivo recordings even at highest quality, so maybe all that is tied together. Just noticed the problems today and there haven't been enough action shows on yet to check out all the stations in the market.

Thanks for your thoughts. Others?
posted by bbranden1 at 4:29 PM on March 26, 2009

A lot of stations are choosing to hold back bandwidth on their over the air digital broadcasts so they can use to for alternate program streams. It looks like OPB is a good example of that. They have an HD stream, an SD version of the HD stream, and then an alternate stream on 28.3.
posted by Good Brain at 4:57 PM on March 26, 2009

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