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Why Does a Screen Re-Draw Make Noises?
grungy asks: "On several computers I have owned, I have noticed an audible noise related to large screen re-draws. A hardware guy once hypothesized that the large memory-move operation was creating electronic 'noise' which was then picked up and audibly amplified by my speaker. I unwired my speaker, removed it from the machine and put it in a different room, and the phenomenon still occurred. At this point I assumed it was something going on/emanating from the monitor itself. Now I have a TiBook laptop with an LCD panel. At quiet moments I can still hear it when I drag windows around. I have tried doing big memcpy's & the like, I don't get the same noise. I've been wondering about this for years. Anybody know what gives?"
Whenever you have a flow of current, you will have a magnetic field generated, and that field reacts with the environment to cause motion. Even though computers are 'digital' doesn't mean that some how they are immune from the all the laws of electromagnetism we use to design analog devices like speakers - it's all the same thing. If nothing else, there is always the earth's magnetosphere to react with like a speaker's coil to it's magnet.
It's the same reason electrical transformers hum, and fluorescent lights buzz.
"I don't know that atheists should be considered citizens, nor should they be considered patriots." George HW Bush
I have noticed an audible noise related to large screen re-draws.
Do the noises sound like sounds?
Do the sounds sound like words?
Are they talking?
Talking to you?
Telling you to do something?
Something like...
Kill! Kill! Kill?
Kill the nassssty hobbitses?
For the precious, preciousssss, preciousssssss
Ring?
Yessssss. Yesssssss. Kill the hobbitses!
Opinions on the Twiddler2 hand-held keyboard?
or at least get them from the grocery store instead of collecting them out in the forest.
That should solve the problem quick.
The hissy-screechy-screech-screech that you're hearing might also be coming from the power supply. To the extent that it would carry into your audio circuit, electrical noise would easily translated to acoustic noise through your speaker/headset.
However, it's also possible that you have a marginal power supply that operates at switching frequencies that approaches human-audible frequencies; or the actual current draw changes from high-speed memory transfers within the graphic sections (board) has a human-audible frequency component to it that actually emanates from (say) the torroids in the supply.
People with very sensitive high-frequency hearing can sometimes tell the brightness of a television screen just by listening...
This could also happen from other activity -- I once had a 386 PC which, when running DOS, would emanate the tell-tale sound when it was waiting for keyboard input. It was kinda neat, actually -- I could go read other things while waiting for a program to finish its calculation -- and I didn't have to keep looking up at the screen...
Just to add to that, there are quite a few people that can hear the extremely high-pitched whine of CRT's scanning - we can tell if a TV is on in a room without looking with it on mute. The channel changing sound is much lower pitch so almost anyone can hear that, not to mention the static discharges that can occur. It's no surprise to us that electronics make noise, in fact sometimes it can be downright painful. I used to have this 32" inch TV that would whine to the point of pain until it warmed up 5-10 minutes later. Of course as I cover my ears everybody else doesn't notice a thing. Good ears can be a curse :(
"I don't know that atheists should be considered citizens, nor should they be considered patriots." George HW Bush
*Turns Calendar Page*
Looks like it's Duplicated backplane dereferencing signal.
You see, the operating system has to keep a buffer of the screen in memory, and similar to dereferencing a pointer, the dereferencing of this backplane, or buffer, temporarily distorts the signal on monitors that haven't been serviced lately.
{DUMMY MODE ON}
Luckily, this is something you can quiet fairly easily. Do you have a screwdriver?
You are hearing noises from yout computer?
Ok, this is what you need to do:
Listen to music. LOUD music. For years on end. Eventually, you will get to the point where you will no longer hear the noises coming from your computer. Problem solved!
Ehh? What did you say? Speak up, son!
I haven't lost my mind!
It is backed up on disk...somewhere...
LCD actually change physical state, i.e. there is a mechanical change. Enough of those at the same time, and there will be some sound. A little like piezo-electric shriekers, but much smaller, and with much smaller movement, and only a single pulse of movement rather than repeated oscillation.
My Psion 5 used to sing a merry song to me all the time as things changed on screen. Almost everything LCD makes these noises in some quantity. I do have very sensitive ears though, so perhaps not everyone hears them.
YAW.
Your head of state is a corrupt weasel, I hope you're happy.
They are all wrong...
It's a little guy in the computer with chalk, drawing the pictures on the screen. Sometimes when the screen "freezes" - it's him taking a break.
After a long spell at the coomputer you can usually hear him gasping for breath.
When he has run out of colours and he only has blue left - that when you get the BSOD.
For problems, seek only the simplest solution, complexity brings with it more problems.
Presumably you're refering to this event at the Homebrew Computer Club back in 1975... (snipped from this article)
The Altair may have been frustrating, but it drove the nerds to experiment, finding real uses for the useless box, turning it from a curiosity to a computer.
Lee Felsenstein
Steve Dumpier set up an Altair, ehm laboriously keyed a program into it. Somebody knocked a plug out of the wall and he had to do that all over again but nobody knew what this was about. After all, was it just going to sit and flash its lights? No.
Roger Melen
You put a little eh transistor radio next to the Altair and he would by manipulating the length of loops in the sofware - could play tunes.
Lee Felsenstein
The radio began playing 'Fool on the Hill'....Da da da, da da da....and the tinny little tunes that you could tell were coming from the noise that the computer was generated being picked up by the radio. Everybody rose and applauded. I proposed that he receive the stripped Philips Screw Award for finding a use for something previously thought useless. But I think everybody was too busy applauding to even hear me.
Roger Melen
It was a very exciting thing, it was probably the first thing the Altair actually did.
On a related note, my old BBC micro used to pick up interference on it's internal speaker, which could actually be used for some basic debugging. You could tell if it had crashed, or whether it was still running round a particularly heavy maths loop, etc...
I'm amazed at the number of answers from the "Slashdot experts" and yet I don't see the correct one yet.
The noise you hear is actually fairly simple to explain. First of all, people should realize that this is not RF noise coming through the speaker, as you tried to explain. This is a noise generated by the vibration of a system component.
Your graphics card is the culprit. Remember that your hardware is full of clocks(vibrating crystals) and switches(transistors). These microscopic components move or vibrate at very high frequencies. Vibration creates noise, as we all know. But, the vibrations(or frequencies) change when the image on the screen changes. Certain colors and certain movements on the screen create frequecies that are perceptible to human hearing and you hear a slight buzz or high pitched whine form your video card.
If you want to test my answer, try changing the frequencies for your display and you will hear the sound come and go. You will also notice the pitch will change when different frequency setting are used.
Some hardware is less prone to this because of thicker cladding or more secure mountings but, they all do it. It's just that some equipment is louder than others.
...bury you TiBook in the forest and leave it there....does it still make screen redraw noises? ;-)
'we can also hear the so called "silent alarms" used in some banks'
What exactly is it you do for a living?! Do you hear these silent alarms often?