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Discussion Starter · #1 ·
I've got the Audio Authority VGA to component transcoder hooked to my HTPC. I'm driving an 848x480p signal to my Toshiba 56H80.


While my output is certainly better than S-Video, it still had more fuzziness than I would like. I've done a full service mode convergence. When I run the resolution pattern on Avia, it looks like I am getting about 325-350 lines of resolution before the pattern becomes indiscernible.


My old Toshiba SD-5109 easily beats this mark, driving well past 400+ lines of resolution on the same pattern.


When I look at the AA pattern, it looks like I am getting what I would best describe as "ghosting" (thou of course I am not driving an over the air signal... it just describes the effect).


So this begs me to ask a few questions:


1. Is anyone else out there using an AA transcoder and getting more than ~350 lines of resolution from Avia?


2. Is the Key Digital transcoder better in this area? Has anyone tried running Avia to check the resolution on the Key Digital?


3. Is 350 lines of resolution the best I can expect with any VGA output from an HTPC, no matter the transcoder?


I would really like to retire my old 5109, but to be honest the picture quality of my HTPC just isn't as good as the 5109. Can anyone help?
 

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mine is keydigital is great, i`ll buy it again if it went bad after 2 years warranty
 

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I have the AA 9A60 transcoder connecting my HTPC to a Panasonic PT-56WXF95 RPTV. I don't have the Avia DVD, but in both 848x480p and 960x540p I get a very crisp image. Every pixel is clearly visible.


I made some test pattern images back when I was calibrating the set that can be used to test the resolution. They indicate that well over 1000 lines of horizontal resolution are visible (when displayed in higher resolution modes such as 1920x1080i, the limit for 848x480p is of course 848). This indicates that unless you have a faulty transcoder then it's not to blame.


I'm guessing since you said the set the set got better results with a standalone DVD player that the problem is with the way the DVD data is being displayed by the computer. If you are playing the DVD in 848x480 mode then the problem is likely due to resampling artifacts. If displayed in a 16x9 aspect ratio the 720 horizontal lines of resolution on the DVD are being resampled to 848. Since 848 isn't much higher, the resampling will introduce nasty artifacts which have the effect of reducing the resolution and creating alternating areas of slightly reduced and greatly reduced resolution at the "beat frequency". If the pattern is being displayed at a 4x3 aspect ratio then the 720 horizontal lines of resolution on the DVD are being resampled to only 640. This will not only reduce the resolution because of the lower line count but also introduce resampling artifacts similar to the 16x9 case, making it worse.


I would suggest creating a resolution with either exactly 720 pixels across (stretched to a 16x9 aspect ratio) so there is no resampling at all when viewing anamorphic DVDs, or with a much higher horizontal resolution such as 1440 which will greatly reduce resampling artifacts (although it may not be quite as crisp as 720). You will need to tell the DVD software to unlock the aspect ratio or fit to the window/screen since the pixels won't be square. Keep the square pixel 848x480 resolution for desktop use or games. You may even want to consider setting up a 16x9 720x480p mode embedded in 540p timings to eliminate overscan and see the whole DVD image without resampling (See the thread: http://www.avsforum.com/avs-vb/showt...34#post1540334 )


- Dave
 

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IMHO the AA transcoder does degrade picture quality a little bit, though it's subtle. When I ditched the AA and started just using RGB there was a slight improvement. The newer Key Digital transcoder is supposed to be very good, but it's also quite a bit more expensive.


I agree with Dave your biggest problem is the resolution you're running, scaling 720 to 848 is going to produce artifacts. Fine vertical lines such as on the Avia Sharpness screen will make this really obvious. I would recommend a 1440x480 desktop running within a 540p timing. Doubleing the horizontal resolution won't produce any scaling artifacts, but at the same time will smooth out the picture somewhat, getting rid of any jaggies you might see running at 720x480p. Don't worry about the fact that it's not a 16:9 resolution, just uncheck the "Keep Aspect Ratio" option in your DVD software.
 

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Discussion Starter · #6 ·
Thanks for all the help! I really appreciate it.


I tried the switch to 720. It did make a difference, but did not solve my problem.


Per my original post, I am getting what I can only describe as "ghosting" or "ringing" on my display. As the term implies, the ringing causes an afterimage which is offset from the original image by multiple pixels. It almost looks like the worlds worst case of scan velocity modulation, except that I have disabled SVM on my set by unhooking the cable.


I'll try to get my digital camera out when I get home tonight to see if I can capture it and upload it to this thread.


As an FYI, can someone tell me what kind of signal\ iming my off-the-shelf DVD player would be sending to my TV? When I send a signal from my HTPC, my TV's convergence gets really whacked out. I have to make extensive adjustments to the convergence. Then when I hook back up my DVD player, the convergence is then all screwed up for it.


I understand that different timings between HTPC and DVD could easily cause convergence differences. But I'm basically wondering if my TV would be "happier" if I matched my HTPC powerstrip timings to my DVD players timings. I'd like to try that experiment, except that I don't know what timing my DVD player uses!


Thanks again for all your help.
 

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I have visible ringing and ghosting on my display as well, mostly in 1280x720p. I too was concerned that it was caused by the AA transcoder and purchased a VGA to component breakout cable for use with my AccessDTV card (in component mode) to see if that made a difference. I also tried a Key Digital transcoder. The ringing did not go away with the breakout cable or Key Digital transcoder. It was hard to see any difference between the three except for some wavy lines at the top of the display caused by both transcoders. Since it did not work any better for me, I sent the more expensive Key Digital unit back. I am now convinced that the ringing on my set is caused internally, possibly by some sort of edge enhancement circuitry (I disabled SVM already). The ringing is very subtle in 480p and 1080i modes, and doesn't interfere with DVD resolution images. In your case the ringing might be caused by the cables connecting the transcoder to the set, or a faulty transcoder.


This web page http://web-star.com/hdtv/projspecs2.html has some tables containing timing and resolution information for DVD players (regular and progressive scan) and HDTV modes. The purple colored table lists resolutions, scan rates, and pixel clocks. Try to make your timings as close as possible to these and see if that fixes it. This chart could be helpful to anyone trying to create any TV or HDTV compatible mode.


- Dave
 

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Discussion Starter · #9 ·
OK, so here is my best attempt at getting a digital photo. It is really hard to capture what the human eye sees.


I see two different problems. First is what I would call "luminance ringing". You can see it next to black shapes. The lighter areas extend out on either side for 5-6 pixels.


I call this "luminance ringing" because the problem persists even if I unhook the two color bearing component cables and only leave the luminance component cable plugged in (Y).


The second problem is "color blooming". You can see how what should be pure black has green and red artifacts. Nothing in the whole picture should have any color, but the image is full of green and red.


This problem goes away if I reduce the color setting to zero on the TV settings.


As you noted, I really fear that these problems are caused by some stinking edge enhancement circuit in the TV that I can't control. But that really confuses me, as my DVD does not show this kind of behavior. I don't know what would be different from my HTPC.


I think I'll try a key digital transcoder just out of desperation. It's cheaper than buying a new TV!
 

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In a roundup, the Key Digital transcoder was found to be better than the AA or RCA unit. The reviewers said it was essentially lossless up to and including 1080i conversion.
 
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