On 2018-03-20 15:18, Xianwen Chen wrote:
Dear Mihai, Although your tone in your email was not pleasant,
You are posting to OpenBSD-misc. Objectionable tone is very common, particularly for users who *appear* to be complaining about immeasurably-small problems that aren't actually significant in the real world. If you wish to remain an OpenBSD user, get used to people being rude. (I am not going to speculate whether this is good or bad, but it is the case.)
If you are right that humans are not able to see the difference between 60 Hz and 59.95 Hz, then something is wrong with xrandr that the actual refresh rate is quite below 60, not as much as 59.95 as reported by xrandr, because I can clearly see the flickering. I do not think that this is a minimal thing, because the flickering screen makes my head dizzy.
Then my suggestion would be to replace the lights in your room, not try to fix a 0.05Hz deviation. The vast majority of systems I own report that the LCDs actually run at 59.95Hz; I've only seen one or two that ever reported 60Hz. This is normal.
In a worst-case scenario, room lighting that is at a very slightly different frequency can cause odd effects, this is known as interference, and can produce a "beat frequency". If the difference is small it's possible you could experience this as flickering. (I believe the flickering is actually an neuro-optical illusion, but you might still be experiencing it.)
I do not think that there is problem with the connection cable, as there was no such problem when the same external monitor is connected to a ThinkPad R52 using the same VGA cable a couple of days ago. I can check the cable connection again tomorrow.
That is irrelevant. You have measured one VGA driver against a completely different VGA driver. Different laptops = different electronics = different results.
I am sceptical whether there is any other source of distortion. I don't know where to start if there should be distortion.
Fluorescent lights, or cheap LED lights - anything that needs a ballast or rectifier. Any of these things can cause not only the beat frequency optical interference mentioned above, but ALSO can cause electromagnetic interference in the cable. Oh, and cheap USB chargers are another common source of really bad EM interference.
And guess what's almost immune to this type of EM interference? HDMI, DVI-D or DP cables. Guess what's REALLY susceptible? VGA cables. Hmm.
The exact frequency of a monitor, regardless of type, is almost always irrelevant to human eyes. Whether it's 30Hz, 47.8Hz, 59.95Hz or 60.0Hz
As you are apparently experiencing real problems, I would check, in order: 1. your cable - switch to HDMI (or HDMI->DVI or HDMI->DP) and get rid of VGA **immediately**. 2. your lights - try it with all the lights EXCEPT regular incandescent / halogen lights turned off. 3. your eyes - get a thorough examination by a doctor; there are some rare conditions that could cause odd things like this. 4. your brain - make sure you don't have a brain tumour (yes, I'm serious, it can cause things like this!)
As to the VGA cable - this is such an important point that I agree with Nick - please go away and don't complain further until you have switched to a digital connection of some sort. I recall that my Dell E6430 was quite capable of producing so-called "120Hz" digital signals, and yours is a generation newer than that. I am 99% certain that your problem will go away with a different cable. (If you want DVI + DP connectors instead of HDMI, buy a Dell E-series dock on eBay for $50.)
-Adam
