[lug] Monitor/Card tweaking - was Re: Color tweaks

John Starkey jstarkey at advancecreations.com
Wed Feb 21 22:33:23 MST 2001

I changed the subject line hoping to promote more people, I know there are several
experts on here who I'd also love to hear from (if they can forgive me for my
inadvertent spam, the move of the week for me, sheeesh :} )  I think this is pretty
important since, for one, the fatigue from HSync can send you home ready for bed. I
felt it at 60Hz and didn't really know why the screen had become so annoying until i
saw it in my peripherals. :}

> There is a modeline FAQ or HOWTO out there somewhere, which I haven't
> looked at in a VERY long time (though I see below you have found it).
> I'm not sure what each timing is, but think of them in general as a
> specification of things like compensation for lag (e.g., an artifact of
> inductance), periods in which things must be blanked, and correction for
> general distortions. Timing issues in general to fine tune your
> particular monitor/video card setup. Anything closer in description I
> couldn't comment on, but there IS a FAQ out there somewhere, I remember
> seeing it a long time ago. You might find more help and information at:
> http://www.hut.fi/Misc/Electronics/faq/vga2rgb/calc.html

This is a great link. Just playing with it for a couple minutes taught me a lot
about the relationships between the vars. Thnks.

> Up until you reach monitor limitations, there is a tendency to gain a

> better picture as greater bandwidth is supported. Bandwidth is a product
> of horizontal scan rate, vertical scan rate, color depth, and
> resolution. Increasing any one item decreases how much total bandwidth
> is available for the others. The dot clock, that faster it is able to
> run, I think increases the possible resolution for a given scan rate.
> However, as a dot clock approaches its limits, its signal might lose its
> nice square form, and start distorting or rounding, which degrades the
> quality of what you see. So you would consider your maximum resolution
> based not just on whether or not you can reach a particular resolution,
> but also on whether it starts losing quality...a better dot clock means
> you get get closer to the max bandwidth before it distorts. Take this
> whole paragraph with a grain of salt, I haven't investigated too closely
> what I think is probably correct.

I follow you. Audio is the same. (as I said, it's the only thing i have to compare
to). I guess you can't distort the input of the card right. It's a set voltage and a
square wave. But once it's analog going out it's possible to distort the input of
the monitor? My monitor is 65MHz. So anything more from the card is gonna bloat the
signal. But distortion in the sense that your talking about is dynamics not
frequency based. Is it possible to create a frequency based distortion by cramming
too much, a harmonic distortion? I know you said you weren't sure.... just thought
I'd ask.

> > 3) Sync pulses, positioning them.... This just determines where the new line
> > will start and end right?
> Yes.

So my monitor has an adjustment for screen width and height. Is it changing the sync
pulses? Makes sense that it is. So i could easily defeat the purpose by raising the
horizontal sync and closing the viewing area in with the monitor. Would the monitor
be more efficient at this than X? Take a load off by lowering the HSync in X and
up'ing it on the monitor?

Thanks again Dean, you wrote a lot, much appreciated.


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