Flickering Curiosity?

N8F8 writes "Why do some people see monitor flicker more readily than others? I happen to be one of the lucky folks who can spot a 60Hz monitor from across the room. Most people seem oblivious to this flicker. Other people can only see it in their peripheral vision. I tried researching an answer and I stumbled on plenty of information about something called 'Critical Fusion Frequency'. There even appears to be quite a bit of research into this phenomena but I couldn't find much information on why flicker perception varies so greatly. Can anyone shed some (flicker-free) light on this?"

Comments

I see Flicker at other refresh rates....

[haplo21112]

...it seems to depend on the day and the lighting, my level of awakeness...and seemingly even mood...

Often if I change from using my laptop on LCD, or Projector back to monitor, I will be bothered by flicker no matter what refresh I set for a while.

flicker sucks.

[grub]

I can walk into an office at work and spot a 60Hz monitor flickering instantly. Usually I'll ask if the person's eyes get tired, etc. and fix it for them. More often than not they report the eye irritations are reduced.

Re:flicker sucks.

[SilverspurG]

Usually I'll ask if the person's eyes get tired, etc. and fix it for them.

Wrong spin. The person's eyes have adjusted to by in sync with the 60 Hz refresh and they are not bothered by it. Your eyes, for some reason, never figured out how to sync.

My eyes sync at whatever refresh is available.

also

[same_old_story]

distance plays a big role on this. from a distance (6 feet +) you can usually spot flickering monitors very easily.

Not just 60 Hz

[Alternate Interior]

There are a number of refresh rates that I notice.

• 60 Hz is painful
• 72 and 75 are usable, but I notice
• 85 looks natural
• 90 is similar to 75
• 100 and 120 looks similar to 85

It doesn't make sense that 90 is worse than anything else at 85+, so perhaps it's just the particular monitor. And I won't claim I can identify everything. I can't differentiate 85/100/120, or 72/75/90. But amongst the three groups of refresh rates, I can identify the group.

Re:Not just 60 Hz

[Anonymous Coward]

Is your computer illuminated by flourescent tubes? Might be something to do with harmonics if you're living in 60Hz Frequencyland.

Hey, tell me I'm wrong. I'm just winging it here.

Fluorescent Lighting?

[Sparr0]

Sometimes I can see it when it coincides with the frequency of the lighting in the room, or is off by some small amount.

Everybody's different

[jgardn]

I'd like to think that I have the same ability because I have spent so much time in front of monitors. But I know a lot of people who have spent many many more years and who still can't see it.

I've marked this one up long ago to one of those weird attributes we're born with or we learn or that is a combination of both. I know that a lot of people thank me for raising their refresh rate, but there are some who can only work at about 60-65Hz and can't stand 75Hz or 80Hz, which is where I am comfortable.

I've also fallen in love with LCD screens. I can finally work without getting tired! Now if only my mind could keep up with my eyes.

I still use a CRT at work and that's led to the pile of notes and graphs and charts I've draqwn up and strewn about my office. I have to take a break from time to time or I can't look at the screen.

Re:Everybody's different

[Anonymous Coward]

I'm with you 110%. As a long-time tech, I've seen the same things for ages. I have to bump up the refresh to gain comfort for myself; I even have had to wear glasses (tinted, polarized, no correction) when I work long hours in front of a CRT. Not so with a LCD, however. And, as you've stated, it varies with other folks, some at higher freqs and others at lower freqs.

Now, for something new (and related). I also tend to see the flicker in the florecent lights. To make matters worse, the two (lights and CRT) are never in sinc with eachother, greatly increasing the effect. This makes headaches more common. Some people are sensitive to the lights, but not the CRTs (if they've been adjust out of the 60hz range here in the US). For clients who are sensitive, I usually end up replacing the lights and the CRTs to get rid of their issues completely.

And, on a slightly different angle, I can also tell you when your flyback transformer is going bad in your TV because.... You guessed it, I can hear the dang things! This leads to the obvious question: are the two sensitivities related? Again, I know people who can hear the buzz of a TV and others who think we're all nuts (I am, but that's unrelated). It isn't just the transformer going bad that is noticeable, but the screen itself to those of us who are very sensitive.

Now, to tie it all together, I have circamstantial evidence that all of this runs in families. My family has it up through my mother's line. Most of my friends not only do not have it, but it doesn't show in any of the family members that I've asked about this (that's most of them, I'm also an Anthropologist). I have found a couple other families where there is a line of parentage with this 'ability'. Not all offspring will inherit it, but, it seems that most do (dominant trait, possibly).

Anybody have anything on all of this?

Lucky?

[Tom7]

Why do you consider that lucky?
I'm often annoyed by effects that other people don't perceive, and I personally find it, well, annoying.

I didn't read TFA, but...

[xami]

..Toshiba, I think, made some tests in cinemas with 30fps and 70fps movies to see howmany people could distinguish between single frames.
Surprisingly, a lot of them couldn't even notice the difference but there was a significant number (15% afaik) who could even notice single frames in 70fps

Audio corollary

[MrScience]

I can pick of the horizontal frequency of almost any television from more than 10 feet away. I can tell when the TV is on before I even enter the room... but everyone else in my family doesn't seem to pick up that frequency (15750hz?).

Re:Audio corollary

[cniebla]

I can pick that noise too, but with an interesting twist: I actually can use it like some kind of sonar, really. Sometimes I'm on my laptop, giving my back to the door in the room, and to avoid a "comming-from-the-back-making-no-noise" joke, I just turn on the TV, with the sound mutted. It can give to me the actual position / movement from even a cat coming by, so no more jokes ;). By the way, where you found that freq.? (15750hz)

Re:Audio corollary

[Flying Purple Wombat]

You mean that most other people can't hear that noise? I thought that most everyone could, and I was the only one who was really annoyed by it.

Most people can't hear it. It used to drive me crazy, I could hear CRTs, ultrasonic motion detectors, and other things that most people can't. As with many things, this is an individual variation. My son inherited this ability, but my daughter did not.

Now that I'm 0x29 years old, I can't hear a CRT unless my left ear is within 6 inches of it (my right ear can't hear it at all). High frequency hearing loss is common as age increases. In my case, loud music and pyrotechnics accelerated the process.

Re:Audio corollary

[cavemanf16]

I get so annoyed with my wife for always forgetting to turn the TV off after turning off the stereo and other A/V equipment because I can hear it, even from a couple of rooms away. I also notice the 60Hz flicker in computer CRT screens, but 75Hz+ is fine. My eyes actually get really tired when trying to use a 60Hz monitor.

I actually think this phenomenon has to do with brain power and raw brain ability for intelligence. I remember my wife mentioning that she read somewhere that if a cat is prone to watching TV, it's slightly retarded because to a normal cat the frequency of images appearing on the TV is too slow - hence it usually ignores it as "motion" since to the cat it's just a picture hanging on the wall that changes too slowly to be considered interesting I guess. Interestingly, we have two cats in our house. I've caught the dumber one looking at the TV every once in a while. I measure dumbness in our cats based on how well they respond when their name is called, whether they are capable of informing me when they need food, how "sneaky" they are when trying to jump on the counter, etc. One of them is good at all of that, the other is definitely NOT. The stupid one just lets our dog pester her to death and starts crying when he's getting too rambunctious, the smart one knows where to "escape to."

I'll have to try that whole "mute the TV" to act as sonar thing sometime though and see if it works for me.

the sound is unbearable

[St. Arbirix]

Who else can hear the sound a television or monitor makes? I can tell from another room when a TV has been turned off because the high-pitched squeal goes away. Those electronic mosquito repellers are equally annoying.

I've read in various places that women can hear higher pitches than men but I've yet to meet anybody male or female who could hear some of the crap I put up with. Walking into a computer lab is the same to my ears as diving to the bottom of a pool.

Re:the sound is unbearable

[dpbsmith]

Hee, hee... when I was a kid I could hear the 17,750-cycle horizontal scanning frequency (as it was then... it became 17,734 at about the same time it became "Hz") clearly. I'd ask adults about it. And none of them knew what I was talking about. When I was about ten I finally insisted that someone turn a TV off and on, with the volume all the way down, in an adjacent room, so that I could _prove_ that I could tell whether the TV was on or off and wasn't just imagining things.

When I was in my twenties, I went to a dentist who used an "ultrasonic" cleaning device that was audible--and painfully loud--to me. I complained. They insisted that I couldn't possibly be hearing it because it was "ultrasonic." I said, "Oh? How do kids react to it?" They said, "Oh, we don't use it on kids, they jump out of the chair when we do." But they still didn't believe that it was because I, and the kids, heard it.

Also in my twenties, I visited the mineral and gem room of the American Museum of Natural History, which I had visited many times with pleasure, and this time I confronted with the loudest "ultrasonic" sound I've ever heard the displeasure of hearing. I'm pretty sure it was higher than 15,750 Hz. Heaven only knows how many DB it was. It didn't even sound like a high-pitched done; it sounded like someone was clamping my head in a vise. It gave me a splitting headache within about five minutes. There was obviously some kind of standing-wave effect because if I moved my head or walked around it would fluctuate; I probably could have determined the wavelength if I'd thought about it, but I didn't.

It got louder whenever I got near some little boxes mounted on the wall about ten feet. They were inconspicuous and painted black but in plain sight.

I went to the guard, and said that it was daytime and he was on duty, would he mind turning off the ultrasonic burglar alarm because it was giving me a headache. He sort of freaked out. He said that they didn't have any ultrasonic burglar alarm and what was I talking about? I said I was talking about the extremely high-pitched, extremely loud sound that was coming from those boxes on the wall, and pointed to them. He insisted that they were not part of a burglar alarm system and were not making any noise.

I don't know if he a) thought I was delusional, or b) was upset because the system was supposed to be top-secret, or whether c) I _was_ delusional... you figure it out.

Well time took its toll on the old hair cells, and I got the twentieth-anniversary special CD of Sergeant Pepper's Lonely Hearts Club Band in 2000 and listened to the band that supposedly has an ultrasonic tone at the end of it... on my headphones... with the volume turned pretty high... and you know what? I couldn't hear a thing.

Maybe I can visit the American Museum's gem room in comfort now.

Re:the sound is unbearable

[ballpoint]

Typical TV sets whine at 15kHz. That's not a very high frequency; most of us _should_ be able to hear that. CRT monitors are a different beast; the >60kHz line refresh should be unhearable, were it not for subharmonics. Try filling your screen with 5 lines of white alternated with 5 lines of black. Chances are you'll hear something. (for the clueless: don't bother to try that on your LCD).

Some other loosely related stuff:

- More than twenty years ago remote controls used ultrasound. I could hear them from across the room, even though they were 40kHz or so. Subharmonics at play again ?

- I used to be bothered by an irritating feeling while studying in the evening in late spring (in addition to have to study during spring evenings). I quickly found out that the cause were bats. My desk was facing a window, which was opened 45 degrees to the inside. The pings from the bats reflected on the glass pane, right into my ear.

- As to flicker: anything less than 100Hz bothers me. I find (compact) fluorescents with a non-electronic ballast intolerable. Things may be better in the US (120Hz instead of 100Hz here).

Re:the sound is unbearable

[St. Arbirix]

Well time took its toll on the old hair cells, and I got the twentieth-anniversary special CD of Sergeant Pepper's Lonely Hearts Club Band in 2000 and listened to the band that supposedly has an ultrasonic tone at the end of it... on my headphones... with the volume turned pretty high... and you know what? I couldn't hear a thing.

CDs, with a 44kHz sample-rate, can only play sounds up to 22kHz. I'd bet anything that the ultrasonic tones can be heard on the LP version of that album. I'd also bet that that section of the album would be perfect for figuring out if you need to replace the needle on the record player or if the album has become too worn.

New LED tail lights...

[Drunken_Jackass]

are annoying to me. I can see them flicker in my peripheral vision and it's damned annoying. I figured that they musts oscillate around 60Hz or so, but does anyone have any more information about them?

Re:New LED tail lights...

[Flying Purple Wombat]

The brightness in some LED assemblies is controlled by pulsing the current at a varying rates. Changing the ratio of on/off time changes the percieved brightness. They really do flicker on the dim settings.

variable refresh rate

[Froze]

Others have mentioned that they only get bothered when switching from one display to another. I think this is because your brain (optic whatever) can vary the uptake rate of information from your eye.

Test it out, try laying on the floor beneath a ceiling fan on low or medium. If you watch fan long enough you can stabilize the apparent interference rotation rate of the blades.

When you can vary the rotation rate at will, you have less chance of being annoyed by flicker since you adjust rapidly. If you can't see the rate change then your eyes can't compensate for the flicker. Hence they get tired more easily.

Nerves and the brain...

[tRenn]

Ok, I'd like to know if there's a fundamental frequency that the average human's optic nerve/brain refreshes that make us comfortable with viewing CRTs at various refresh rates?

Human Perception

[Anna Merikin]

Human perception varies widely. In the season he hit .406, Ted Williams, in answer to the question, "How do you hit so well?" replied, "I wait till the ball is as big as a watermelon and I can see the stitches and the printing on the hide and then I smack it."

To explain how he alone avoided a terrible accident around a blind curve during a Grand Prix roadrace, Juan Manuel Fangio explained that as he drifted around the turn at about 120 mph, he became aware that the crowd along the side of the track was not watching him, but had turned their faces ahead and that gave him the clue to slow down as there must have been big trouble in the curve.

Human perception varies greatly, or did I already say that?

I do not usually see flicker, but some CRTs are better or worse than others. I cannot tell the difference between smoothed fonts and others. But I can sure hear a tiny bit of distortion above 10kHz! Even so small an amount that others cannot detect it drives me into the pain zone, so I have to choose my audio components very carefully.

Human perception varies greatly.

Re:Shouldn't it be?

[Nynaeve]

What's the refresh rate on life?
5.391 × 10^44 Hz

Re:Beats

[Fascist]

A/C is being provided at 60 Hz.

Most countries privide AC at 50Hz. Only a handful of countries use 60Hz, even though it is the most effective for delivery of AC over long distances. Nikola Tesla recommended 240V at 60Hz after experiments with AC.