Digital Comb Filters on HDTVs

[BrokenVisage]

So I'm about to pick up an HDTV, the 2 TV's I came down to were one with no HDMIt a 3-line digital comb filter and one with DVI but only a 2-line digital comb filter. The one with HDMI like 50 bucks more and had a few little nic-nac's from Philips on it too so I got that (should be here in a week). I got a little spooked when I read a review on this TV that said watching sports was impossible because of dot crawl during fast motion video (the type of thing I thought comb filters were suppose to fix). Now I'm thinking I should have got the one with a 3D filter and am just crossing my fingers that my set doesn't have this issue since I plan to watch NOTHING but sports on this TV. Could someone explain exactly what a comb filter does and maybe give your experience with watching sports on HD if you have a TV with one? Thanks.

 

[BrokenVisage]

*burp*

..excuse me!

 

[BrokenVisage]

 

[YOyoYOhowsDAjello]

I have no idea on this one.

Try AVSforum?

 

[BrokenVisage]

Originally posted by: YOyoYOhowsDAjello
I have no idea on this one.

Try AVSforum?

Yeah I would've in the first place but figured to give Video a try before having to create an account over there.

 

[Pete]

Maybe wikipedia has detailed info, but I believe those filters (2 line, 3 line, "3D," "3DYC," etc.) only work on the RF/coax input (e.g., analog cable or an OTA SDTV antenna) and *maybe* composite. I don't think it affects S-Video, component, DVI, HDMI, or any other, newer interface.

I *think* 3-line is better than 2-line in that it filters across more of the screen, but don't quote me on that. There may also be differences in implementation, so A's 2-line filter may be better than B's. Google should provide a more definitive answer.

 

[xtknight]

Originally posted by: Pete
Maybe wikipedia has detailed info, but I believe those filters (2 line, 3 line, "3D," "3DYC," etc.) only work on the RF/coax input (e.g., analog cable or an OTA SDTV antenna) and *maybe* composite. I don't think it affects S-Video, component, DVI, HDMI, or any other, newer interface.

I *think* 3-line is better than 2-line in that it filters across more of the screen, but don't quote me on that. There may also be differences in implementation, so A's 2-line filter may be better than B's. Google should provide a more definitive answer.

Well doesn't the Y/C separation imply S-Video? (edit: never mind)

http://en.wikipedia.org/wiki/Comb_filter
Confusing.

Here's some decent info: http://members.aol.com/ajaynejr/vidcomb.htm

 

[BrokenVisage]

Originally posted by: xtknight

Originally posted by: Pete
Maybe wikipedia has detailed info, but I believe those filters (2 line, 3 line, "3D," "3DYC," etc.) only work on the RF/coax input (e.g., analog cable or an OTA SDTV antenna) and *maybe* composite. I don't think it affects S-Video, component, DVI, HDMI, or any other, newer interface.

I *think* 3-line is better than 2-line in that it filters across more of the screen, but don't quote me on that. There may also be differences in implementation, so A's 2-line filter may be better than B's. Google should provide a more definitive answer.

Well doesn't the Y/C separation imply S-Video? (edit: never mind)

http://en.wikipedia.org/wiki/Comb_filter
Confusing.

Here's some decent info: http://members.aol.com/ajaynejr/vidcomb.htm

Wow, good info, thanks guys.

Pete: So you're saying if I connect my cable box to the TV through regular (if you consider $40 shipped monster cable 'regular' ) componenet RGB cables, the comb filter doesn't even come into play? So with everything being equal, the comb filter (digital or not) doesn't effect HD signals sent over the cables you mentioned above and I probably shouldn't worry about just having a two-line digital filter ruin any fast motion sports I watch?

 

[xtknight]

Nope, the comb filter doesn't even come in to effect unless you use the coax, I believe, but don't hold me to it. 'Digital' comb filter refers to the fact that it's digitally implemented so it can do its job a little better.

 

[Pete]

I don't know how HD changes things, but AFAIK, the comb filter only comes into play with coax. Again, you'll want to find a second (and educated) opinion on this. Looking at that wikipedia page, I'm not sure an HDTV decoder counts as an NTSC TV decoder, so I still believe (read: that's a weaker endorsement than think, let alone know) comb filters still just apply to a standard-def signal coming into your TV via coax.

That second link says, "A comb filter is needed for the TV to show fine picture detail from standard broadcasts, laserdisk, and other composite sources." Without having read any further than that, I'll take an educated guess that that supports my contention that the comb filter is used with coax and extends it to the ubiquitous yellow composite connector. The reason? I believe only those two "composite" both luminance and chroma on the same line, whereas S-Video, component, DVI, and HDMI all separate the two.

Actually, FiringSquad wrote an article on Monster Cable vs. regular cables for consoles a few years back, comparing S-Video cables, IIRC. Maybe that has info on this in layman's terms. But xtknight's links probably hold your answer, if not in the easiest-to-digest terms.

 

[xtknight]

Well there is nothing to separate or fine-tune in an HDTV MPEG-2 transport stream. The comb filters are definitely not used for digital sources. There's something worth noting however: if you have an external HDTV tuner like me, it will output coax (among other things). Once you route that coax to your TV (whether analog or digital), the TV will use its comb filter.

 

[BrokenVisage]

Nice explanations fellas, I think I finally wrapped my mind around it now.

Originally posted by: xtknight
Well there is nothing to separate or fine-tune in an HDTV MPEG-2 transport stream. The comb filters are definitely not used for digital sources. There's something worth noting however: if you have an external HDTV tuner like me, it will output coax (among other things). Once you route that coax to your TV (whether analog or digital), the TV will use its comb filter.

I'll be using a STB tuner too with my digital cable box, so the coax cable will go into that box with has component outputs that go to the TV. So in that process I do use coax to receive the cable signal but it doesn't go directly to the TV, would the filtering take place in the STB then?

 

[Peter]

If you're receiving progressive format HDTV (those resolutions that have a "p" suffix), you don't need a deinterlacer anyway. It seems that most stations are shooting for 720p, so this might just as well be a non-issue in real life.

 

[xtknight]

If Device A inputs coax, Device A's comb filter will be used. So whatever you input coax in to will have a comb filter unless it's a splitter or something.

 

[Mark R]

I'll be using a STB tuner too with my digital cable box, so the coax cable will go into that box with has component outputs that go to the TV. So in that process I do use coax to receive the cable signal but it doesn't go directly to the TV, would the filtering take place in the STB then?

There should be no filtering in that situation. The comb filter is used for one purpose only - it's used to process a composite (analogue) signal for display or recording.

The cable signal is digital (so comb filtering is not required) and a new analogue signal is generated by the decoders in the STB. Because the STB is generating the analogue signal (and not processing one that is already available) there is no need for comb filtering in the STB.

Only an RF, or composite video connection to the TV requires comb filtering. S-video and component don't require filtering - the comb filter is only used to seperate the luminance and chrominance where they have been combined onto a single wire.

 

[BrokenVisage]

Originally posted by: Mark R

I'll be using a STB tuner too with my digital cable box, so the coax cable will go into that box with has component outputs that go to the TV. So in that process I do use coax to receive the cable signal but it doesn't go directly to the TV, would the filtering take place in the STB then?

There should be no filtering in that situation. The comb filter is used for one purpose only - it's used to process a composite (analogue) signal for display or recording.

The cable signal is digital (so comb filtering is not required) and a new analogue signal is generated by the decoders in the STB. Because the STB is generating the analogue signal (and not processing one that is already available) there is no need for comb filtering in the STB.

Only an RF, or composite video connection to the TV requires comb filtering. S-video and component don't require filtering - the comb filter is only used to seperate the luminance and chrominance where they have been combined onto a single wire.

So for something like hooking up a PS2 to the TV where video is only going through the one wire a comb filter is used. But not for something like a DVD player using component cables where 3 wires are used to transfer video. It just seems like not a big deal for these high priced home theaters where everything is digital anyway, but it could just be another thing to put on the stat sheet to try and sell somebody with features.

 

[Peter]

If the DVD player is feeding a progressive signal not an interlaced one. It can't feed progressive through the SVideo cable. On the component cable, it can, but it doesn't have to.