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  #1  
11-15-2012, 08:27 AM
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Hi, When we do a loop of pback and record it then playback the recording and record it again and playback and record this we notice the brightness level decreases each time, may we ask what can be done to keep the brightness level constant and general picture quality. Is there a device that can go between the player and recorder for the loop to be successfull? Is dc restoration to do with this?

Regards John


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  #2  
11-15-2012, 08:29 AM
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This is often referred to as "nth generation" copying -- aka, a copy of a copy of a copy of a copy.
The further you get from the original, the more loss there is.

It's by far the worst on video tapes (analog playback/recording), but the same is true of compressed digital formats like MPEG-2.

What is your playback and recording media?

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11-15-2012, 08:14 PM
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Hi DAQ. We thought using a digital video camera and a dvd recorder would keep brightness level constant and video quality but no. Is there a circuit to build or device for such a process?. Thanks DAQ
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11-15-2012, 08:41 PM
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Yes a device with something called procamp settings would let you adjust the brightness to be slightly more, which should equalize out your recordings. Another solution is to use PC based capture rather than a DVD recorder; this is because the capture software will have a brightness adjustment. Even so, there may be a slight change in brightness if you continue to do enough loops; for example after 4 loops you might have to move the brightness one click down for one loop, then put it back to the optimal level.

I've also done this in video by: set your PC to dual monitor mode with clone, then on one of the outputs attach a VGA to S-video converter, and send that directly to the video capture card, then display the capture on the screen, and you will see the feedback live.
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11-16-2012, 07:36 PM
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Hi Jmac 698 and thanks so much for the update m
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11-18-2012, 06:42 PM
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What you want is a proc amp. The Elite Video BVP-4, SignVideo PA-100, and older Vidicraft units are commonly suggested.

While software proc amps can work, it heavily depends on the quality of the hardware, and the capturing software. And whether you can use it depends heavily on the CPU and RAM available on the computer. It goes both ways -- sometimes the software proc amps work great, and sometimes they're almost useless. And then some can cause dropped frames, audio sync issues, and what-have-you. So be aware of that.

The hardware is generally more foolproof, though you want to use good quality shielded cables, as well as clean power sources. And then because all of this gear will be used, you'll need to verify it's in proper working order. They usually are, but some are pretty beat up.

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