Are you in PAL territory (EU) or NTSC territory (NA)? I seem to remember France from our conversation about the wolf the goat and the cabbages. That would mean PAL and instead of 60 the refresh rate would be 50, and the Horz. rate would be different too (one of us would have to look it up, and since you're the one who actually needs the infomation... ). How are you connecting to the "TV", is it an S-Video or composite video (the yellow RCA phono jack) connection? Or are you connecting with a VGA/SVGA, DVI/HDMI, ... or similar type of thing like a monitor?

As I understand it, the Dot Clock Frequency is associated with your graphics card, not the TV.

If you really want to try and understand how the modelines work, there's some really nice links to some websites from the Knoppmythwiki. I learned a lot about TVs, displays, and modelines from there. I suggest trying the XF86Config-4 HOWTO. There's good links in that how to.

tjc: yes I'm french but I live in Canada now. (Montreal).
So I'm using NTSC-M amd 60Hz, (I think). I'm using S-VIDEO for TV.

gamelyn31: ok, but I wanted to know what it was for.
I looked at KnoppmythWiki but I don't understand yet.

I'd like to set my TV as good as possible. The picture of TV, or recorded shows is great on my TV, but the OSD and the GUI are too large for the screen. If I decrease OverScan, TV picture becomes round (not square anymore) and a wave effect appears on the top.

Moreover, small letters in GUI are totally blur and xterm is not readable at all.

So , that's why I'd like to know and understand everything to try different settings which could optimised my display.

zetoune - try this link from the wiki: http://knoppmythwiki.org/index.php?page=HDTVSetupHowTo

in Section 3c. of the howto, there are three links about "do it yourself modelines." Those links should answer most of your questions, including Dot Clock Frequencies. I'd try to explain it to you myself, but I'm still pretty new to this as well, and I'd probably make mistakes.

Thx gamelyn31. I think I understand now.

To sum up, to get a good modeline
- I need the resolution I want (what is the best resolution for a standard 27" TV? 800*600, 640*480, 720*480, 480*480, something else?)
- DotClock frequency of the videocard (and my TV as well)
- maximum vertical frequency of my TV (it's 60, isn't it?)
- min & maximum horizontal frequencies of my TV (it's 30-50, isn't it?)

Do I have to check "interlace" in modeline? (Also, Do I have to uncheck De-Interlace in setup?)

You don't need the dot clock frequency, it's redundant. Don't obsess.

Since standard-def TV is limited to 480 lines, you're fine with 640x480 (which is a common resolution for TV-out on a video card--not sure whether 720x480 or 480x480 would be supported).

I don't think checking "interlace" helps any as the composite or s-video output is already necessarily interlaced.

Have you seen the FX5200 example on the wiki? It's what I use on a 27" NTSC TV connected via S-Video. This of course presumes that you're using an Nvida based video card...

I manage overscan using the nvidia-settings utility. There are several adjustments you can make with it which will give you smoother text crawls and sharper characters in crawls, xterms and the like.

tjc : I have a FX5200 and I've ever tried sample shown on the Wiki.
But with this XF86Config file, I got oblique strips in my TV. That's why I kept the nvidia tv-out sample.

For overscan I use nvidia-settings too. it's great. But I played with "sharpen effect" and I couldn't get a sharper image.

I'm stilling searching

Dialing down the anti-jitter control (I forget the exact name) can help improve sharpness significantly. It's usualy set too high by default.

No idea about the funky diagonal stripes thing. It usually means you're not getting good sync.

The fx5200 example uses the 800x600 modeline by default. You might have better luck with one of the 640x480 modelines...

to force the use of 640x480, I just have to comment lines where is 800x600?

I'm gonna look for the "anti-jitter" control. It's in the nvidia-settings too?