Notch Filters

[number_15]

Hello again, could someone please just answer a couple of quick questions. I have read that a notch filter is just a simpler and less effective method of improving edge colour detail than a comb filter. I have also read that comb filters only work on composite signals because they are not needed with better connection types such as RGB. I was just wondering if notch filters were similarly redundant with RGB? I have a Sony FX65 and use the RGB scart for my dvd player, I was trying to improve the known ghosting problems etc and just wondered if turning the notch filter on (default is off in the service menu) would help matters for dvd playback or otherwise? I was reluctant to change any service menu settings whose uses I didn’t fully understand (I’ve read that setting the TV with features it doesn’t have can cause major problems).

Thanks Again
Billy

[symanski]

Ah, notch filters. What these do is to act as a block to a certain frequency, creating a notch in what frequencies they can pass. When designing these, you've got to be careful that you've got just the right frequency otherwise your notch will be sitting to the side of the frequency you want.

So how does that help you here? Well, with a composite signal you've got the colour information mixed in with the luminance. These interfere with each other at a particular frequency, and you've guessed it, that frequency is where you put your notch filter! A comb filter does this even better.

But the best way is to avoid the problem in the first place! You only find the problem with composite video, which is why us Home-Cinema buffs avoid it like the plague! RGB, Component and S-Video don't suffer from cross-colour interference because the colours are never mixed up like they are on a composite signal.

If you have a ghosting problem with your DVD player, this is probably a completely different problem. Can you elaborate further on this? First suggestion would be to buy a better SCART cable, but if you've already got one then the problem must lie elsewhere.

All the best,

Dr John Sim.

[number_15]

Hi and thanks for the help it’s greatly appreciated. Unfortunately the ghosting problem is a known “feature” of the FX65 and is talked about readily on the KV-TWEAK site amongst others, I might buy a different scart cable though (I have a better than poor one but not a great one).

Regarding the notch filter, will setting this to “on” improve the picture on the standard aerial RF feed? Has anyone tried it on this set (obviously I don’t want to damage the set by fiddling with settings)?

Thanks Again
Billy

[symanski]

Sorry, not up to speed on the FX65 "feature".

Yes, use the notch filter on the RF input, as well as any composite inputs. If you're using S-Video or RGB, you should keep this filter off.

All the best,

John.