VBI "noise" caused by broadcasters - AVS Forum
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post #1 of 6 Old 10-11-2008, 04:21 AM - Thread Starter
 
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Several boxes such as the CM7000 and DTVpal and Zinwell ZAT show "garbage" at the top of the image. These lines are mostly digital data such as closed captions being sent "above" the actual image on old NTSC analog signals. They are part of the signal's vertical blanking interval (VBI) and normally are hidden by the plastic edge of your set.

While watching NBC's Today show, they displayed a 4:3 videotape surrounded by a graphic on the left & right side of the image. The pillars on the left and right looked flawless, but the center part of the image had a visible VBI.

This indicates to me that it's not the box that is the problem (otherwise the VBI would be imposed across the entire width of the image). It is the *broadcaster* incorrectly framing the image, making visible part of the 4:3 analog videotape that was supposed to be invisible.
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post #2 of 6 Old 10-11-2008, 04:42 AM
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I've never noticed it on Digital or even on my LCD screen on analog. I used to see it all the time on my old CRT screen.
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post #3 of 6 Old 10-11-2008, 05:24 AM
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According to someone I talked to at a station a few years ago, it can be removed by the station (assuming someone working there actually knows how to fix it, wants to and has permission). IOW, not likely.
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post #4 of 6 Old 10-11-2008, 06:41 AM
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What box do you have? I've got a Zenith DTT-901 and have never once seen the VBI.

My friend who has a Westinghouse LCD TV and OTA DTV sees the VBI a good part of the time.

Usually, it's kept in there for CC data.

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post #5 of 6 Old 10-11-2008, 07:02 AM
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Quote:
Originally Posted by mattdp View Post

What box do you have? I've got a Zenith DTT-901 and have never once seen the VBI...

I see VBI on my Zenith DTT-901. But only on a couple of channels. I do not see it on my HDTVs, but they aren't letterboxed, either, so slight overscan takes care of it.
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post #6 of 6 Old 10-13-2008, 04:10 AM - Thread Starter
 
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In the example I cited, the VBI was only on the 4:3 part of the screen, not on the NBC "pillars" on the sides. NBC had improperly converted their 4:3 analog tape.
Quote:
Originally Posted by mattdp View Post

What box do you have? I've got a Zenith DTT-901 and have never once seen the VBI.

The Zenith chops-off the top 5 lines of the picture, while the other boxes display everything. The VBI is there, but the Zenith crops-it out. Unfortunately that also means it crops-out part of the actual picture.

The easy fix is for stations to stop capture exactly one NTSC scanline per DTV scanline. NTSC's visible frame is 486 lines, and DTV is 480, so if the analog-to-digital converter is properly centered, you won't see any closed captioning data. Unfortunately the broadcasters don't properly center their devices.
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