Re: [gentoo-user] multiple monitor refresh rates and broken brains (was: fonts and bad eyes)

[Joakim Gebart]

On Sat, May 17, 2014 at 9:37 PM, Greg Turner <gmt@×××××.us> wrote:
>
>
> On Sat, May 17, 2014 at 4:21 AM, David Haller <gentoo@×××××××.de> wrote:
>>
>> Oh, and _very_ importantly: get a _GOOD_ matt monitor if you haven't
>> yet.
>
>
> Apologies, David, for hijacking your really good question-thread, which I'm also very eager to hear people's answers to.  But, this reminds me of something I've been pondering lately...
>
> I think maybe refresh-rate discrepancies are subtly evil in multi-monitor setups.  When I look at my 59.9 kHz apple cinema next to my 60 kHz POS Dell throwaway monitor, something spooky clearly happens in my brain -- if I get up close and look carefully, the pixels seem to rather dramatically "swim" near the bezels between the two monitors, in a way that reminds me of a migraine prodrome (perhaps because, to some degree, that's exactly what I'm inducing in my brain, by exposing it to high-frequency polyharmonic interference (presumably, there's a >0.5 MHz harmonic between those two displays, no wonder my brain doesn't like it!).

From your description I am suspecting that your problem is not due to
59.9 Hz vs 60.0 Hz but rather poorly tuned analog to digital
conversions in one or both of the monitors, you could use a
high-frequency test pattern such as [1] and press your monitors'
"Auto" button (or select Auto configuration from some menu). The high
frequency pattern will help the monitor during the auto configuration
and let it tune the phase of the analog signal more precisely. This is
if you are using a VGA cable and not something digital, such as DVI or
HDMI. If you are having the same problems with digital signalling you
probably have a bad cable.

>
> In practice, I don't seem to have had any huge problem from this (and I'm going to get rid of that crappy Dell soon, anyhow) but I have heard reports from people claiming this type of thing caused eye fatigue and headaches.
>
> My semi-baseless theory is that, so long as the remainders of the greatest common multiples of your various monitors' refresh-rates form nice clean ratios like 1:2, 2:3, etc, you probably won't fry your wetware input circuitry looking at them.
>
> However, if, as above, there are ugly harmonics, I suspect it might be pretty bad for some people.  If, like me, you're too cheap for the 100% solution of buying identical monitors, maybe just try to ensure everything you buy supports standard 60kHz standard modes, or even go read the 1990's-era ModeLine authoring FAQ's and attempt to actually understand the problem and fix it, if you're feeling ambitious :)
>
> Anyhow... we now return to our regularly schedule programming...
>
> -gmt

[1]: http://pixelmappat.nu/

Best regards,
Joakim