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Discussion Starter · #1 ·
Just wondering if anyone out there has experienced this same problem or has any advice on how to remedy.


I'm in the Phoenix area and can receive all the OTA feeds at a good signal strength. I'm using a DTC-100, RCA VGA to Composite Video converter, and a Toshiba TN55X81(4:3). For the most part, it's GREAT. My problem is when my DTC-100 is in 16:9 mode there is visual static that appears with some content between the picture and letterbox. The problem is consistent with each station:


NBC, ABC - All national feed content (except HD content) displays static at top of picture. Disappears with local content.


FOX - Local content displays static at bottom of picture.


It has been suggested that this static is closed-caption data being displayed in the Vertical Blanking Interval of my set and that I need to increase my overscan.


While I agree, it sounds like it is probably a problem with Closed-Caption data, my question is will adjusting overscan on my set really remedy the problem? I guess I'm not totally clear on where the letterbox is generated. I thought the image, along with the letterbox, was generated by the DTC-100 and the entire signal sent to the monitor. If this is correct, I would think that increasing overscan would just make the letterbox narrower and push the image off the sides? The reason I say this is that I've played around with the WID and HID settings and it does just that, increase/decrease the size of the entire picture, including the letterbox, not just the image portion.


Any advice would be GREATLY appreciated. I've gotten to where I just ignore the static, but my wife finds it annoying and I end up having to switch the picture to 4:3 mode (yuk!). Not only is the picture quality noticeably worse, but it really bothers me not knowing what I'm missing in the outer thirds of the picture!


Thanks in advance!
 

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There are actually two data signals that might be visible. One is closed caption and V-chip data on line 21. This would look like fairly wide bars that appear in nearly random bursts. The second is the Nielsen 'AMOL' data on line 22 that is used to automatically verify that programs and commercials are being broadcast correctly by local stations. This signal appears as much narrower dots that often appear to flash at a once per second rate. Depending on a station's upconvertor settings these might be passed through as video and be visible even with the gray bars.


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Discussion Starter · #4 ·
Thanks, Bill! Turning the grey bars back on definitely covered it up.


So does this mean that turning the gray panels off does not make the panels black, it makes them disappear? If so, then where is the letterbox generated (by the DTC-100 or the TV)?


Also, when the gray bars are on, it seems to chop off a bit of the top and bottom of any HD content. Does this sound right?


The reason I'm asking (and pardon my ignorance) is I would like to get rid of the gray bars by making the proper adjustments wherever needed. It sounds like I need to increase the overscan somewhere so it pushes line 21 and 22 into the letterbox, but as I said in an earlier post, it seems that any adjustments I make to the TV only increases the size of the entire picture including the letterbox, not just the picture area.


What am I missing???



[This message has been edited by tmharper (edited 03-19-2001).]
 

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The original intent of putting Closed Caption and other ancillary data at the very top of the video was to be able to provide these services without affecting what the viewer sees. In most cases, "standard" TV sets significantly overscan hiding the data. If you have an older analog TV (one with a vertical hold control), you can cause the picture to slowly "roll" vertically by turning the vertical hold control and see the hidden data.


Newer TV sets, especially projection sets, give the viewer the ability to control the amount of overscan; indirectly causing the data to be viewable. When viewing an analog signal, there is nothing the TV station can do to hide this data. In the digital signal, we are looking at ways to move this data into the bitstream we are transmitting - again hiding it from viewers. Unfortunately, the standards are still either not completed or have not been implemented by the stations or the equipment manufacturers.


In the past, when our plant was analog, I could insert a piece of equipment that strips the data before sending the video to be converted to digital and sent to the DTV transmitter. While converting our plant to digital resulted in a very noticeable improvement in our signal quality, it also means we don't have a data stripper we can insert before the DTV transmitter.


That doesn't mean we have stopped trying to solve this problem, but there are other priorities - like porting closed captioning to DTV, getting the PSIP working 100%, solving the glitch when we insert local commercials into true HD programming, completing the automation, etc...


I've sort of gone off track - to answer some of your questions... The grey bars does mask some of the video, very much like your analog TV's overscan masks the video. Turning off the grey bars simply allows you to see what the TV station is transmitting.


The letterbox can be generated in several places. At KPNX, the letterbox can be generated in the upconversion process (normal programming) or the programming can be sent in letterbox mode (ER and true HD programming). Certain TV sets can also stretch the picture to create letterbox. I believe most HD sets will display KPNX's digital signal in the mode we create it in.


I hope this answers your questions. Feel free to contact me directly if you have any others.


Karl Voss

KPNX-TV/DT

[email protected]

 

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Discussion Starter · #6 ·
Thanks for the reply, Karl.


So based on all the feedback I've been given up to this point, it seems my only options are to keep the grey panels on, watch the effected content in 4:3, or just ignore it.


The lack of threads regarding this issue just led me to believe there was an adjustment that could be made somewhere in my equipment to eliminate it.

 
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