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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
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...
Not quite true.
Remember that light itself is electromagnetic radiation. The change in screen color (as suggested by one comment) might be enough to make some small amount of noise.
More likely, it's an induced response from the screen material to the changing charges across the screen. An LCD works by putting an electric field across a liquid crystal to allow/block light. As you redraw, those electric fields are changing. Those fields might have a small effect on actual material the LCD is made of. Those materials might have a small sensitivity to electric fields, and there is almost certainly some small charge even from dust on the screen.
So... after all that, it's my guess that the clicking noise (I've heard it too, you're not insane) is portions of the plastic on/in the screen either expanding out or contracting in with the field, essentially "popping" in an out.
Another thing it might be is electrically charged dust (dust does not have to be neutral) moving around on the screen. Try dusting your screen and seeing if that does anything.
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.
You got an MSI for a reason.
;-) Designed for overclockers, with the stability overclockers (not sysadmins) expect. Usually the higher cost for these boards nullifies overclocking benefits, but just like people who add "Type-R" stickers to their cars, the people buying these boards don't care.
From my experience, here's what I've found as to why to buy from different motherboard manufacturers:
Soyo: A value board. Lots of stuff crammed on for a good price, or hardly anything on it for a bargain basement price. Not a bad board, but not top notch.
MSI: The die-hard motherboard. Might not be a cadillac, might even have some annoyances, has no luxuries at all (usually), but dammit, they _always_ work, and are reasonably priced.
Asus: The "high-end" motherboard. Just like cars, where more money gets you some bells and whistles, but not always more reliability, Asus motherboards are bought by people trying to show their box is "awesome" because it cost more. If you look past the pricing, quite a good board. Lots of support, too.
ABIT: The ricers mobo.
PC Chips (aka any weird Chinese name you can think of): When cheap-enough (Soyo) isn't. Zero support, stolen/fake parts, and a high failure rate. But look at those prices! Often found in low-end Brand Name machines.
ECS: PC Chips "top-notch" line. A well supported stolen/fake parts brand motherboard.
A-Open: Overall, pretty good stuff. Good in most categories (price, support, quality, performance) but fell out of favour with after providing me with a broken BIOS for an old board, ruining it (didn't have an EEPROM burner at the time). Definately not an overclocker's board.
Shuttle: Haven't had enough experience with their product. Boards I have seen were reasonable.
Tyan: Haven't seen too many of these boards, but people I know tend to regard them as a good for a frankenserver board.
There's others (gigabyte, biostar [pc chips?], intel, DTK, etc) but I simply don't see these boards in operation much anymore.
So that's why they sold you MSI. You came in telling them your board was causing you hell, so they gave you the bulletproof one. I'd have reccomended you to stick with it and buy a PCI sound card (heck, if it were my store, I'd probably just give you a used SB PCI128), but hey, that's just me. Then again, I'd have replaced your board with an MSI with the Nforce2 chipset, so you'd have decent sound to start with.
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
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.