It's been awhile so this may be a bit rough around the edges.
A comb filter is used to separate the color signal (3.58Mhz) from the luminece signals. Way back when color TV was being introduced they found they did not have enough bandwidth to keep all of the signals necessary for a color picture seperate from one another. They are beat together to reduce the bandwidth requirement. Essentially it is just a notch filter to remove all of the color signal from the luminence(brightness) The little color dot crawl is one symptom of a bad filter. A digital comb filter is just a better form of notch filter.
Yes, it will make any RF signal better.
I don't think it will help on gamecube or a DVD. The signals are already separate and the comb filter has no effect on s-video or component video. It will help if you use composite inputs.
You will see some but not an overwhelming improvement on a 20" TV between a digital comb filter and a 3-line comb filter.
cnet
In order to transmit a color TV show to your home, a station must combine the audio and the composite video channels, which it broadcasts as an RF signal. Then your TV has to separate the sound and the picture so that you can view your show. However, you'll get cleaner pictures and sound if you don't combine the signals. And that's why you find separate audio and composite-video cables on most VCRs, satellite boxes, and video game consoles.
vidgames.com
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