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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?"
Is it associated with a large change in brightness? Like in drawing a white box on top of a black area?
It could be static electricity, as it is suddenly going from one number of electrons to a very different number of electrons hitting the screen.
Gee, it's great to have an electrical engineer as a dad...
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
Maybe it's all the little ``gates'' opening and closing inside the computer as the electrons flow through system. I have created this same noise effect by ping flooding a host in a test lab environment on a 100Mps Full-Duplex switched network---the network card was actually a four port and I may have been pinging all four interfaces from different systems.
LCDs do not have the electro-magnetic radiation that can be picked up by passing DOJ vehicles for license validations.
In late 1997, a secret comittee was formed and ushed in a new era of aural-based tempest radiation sensors. They created a bill that stipulated all LCD monitors needed audio broadcasting capabilities for governmental remote viewing. It was rushed through congress during secret underworld briefings and eventually passed at the Grand New World Order Council, codified in January, 1998.
Today these signals are still somewhat perceptible in the lower frequencies, but they emit a wide spectrum for large data broadcasts. Simple listening devices can pick up many user metrics, and are not limited to merely what's displayed on the screen.
I hope this answers your question.
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?
have you tried turning /up/ the volume of the speakers? /internal/ speaker?
yes, I know "The speakers unplugged blah blah blah", I'm not saying that it doesnt exist when there are no speakers, but the speakers could indeed pick up the noise.
When I heard this noise, however, I looked up on google, it said to turn your soundcard volume down from 100%, and boom it goes away.
Now let me ask you this: have you unplugged your
-- 'The' Lord and Master Bitman On High, Master Of All
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...
I've heard this on every computer I've owned, going back 14 years to my Apple IIgs. Any CPU operation (tight loops reading memory especially) could be heard as pitched tones on the audio out, especially noticable when listening with headphones. On the IIgs, I had a stereo "Audio Animator" card and always figured it was crappy RF shielding. You could hear a scale, tones changing as you moused over each item in a menu.
;)
But it happens on my other computers too, to larger or smaller degrees. On my TiBook, it's pretty noticable when the fan/drive are spun down. I program in Cocoa/GL and you can hear the tone change just by creating an NSTimer with different frequencies, and using it to do graphical operations. Most of the time, this results in a low 60Hz "hum."
I think it's due to RF interference between the audio portion of the board and whatever else is nearby. It seems more prevalent on laptops where everything is packed closely together but it's not limited to laptops, or LCDs.
Somebody should write an app that plays one-channel melodies with the RF noise...
*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...
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.
Before, with CRTs and cheap LCDs, anytime that I moved a big window (typically bright, say all white), and wiggled it around the desktop, I heard something similar to a, "wheeeee, weeeeee" kind of sound (the 'wheee' matching the window movement). Of course, this was a very very high pitch sound; a quieter and higher pitched version of the whine that TVs and crappy old CRTs make. Now I have a new and really nice LCD... I can't really hear anything, but then again, maybe I'm just getting old.
;)
Isn't it great to know you have good hearing though?
This is a little OT but... back when I was a kid, I think I had even better hearing... I used to stay at my grandparents' house, and I could sense people walking down the hall to my room, no matter how quiet they were. The floor didn't squeak, and my grandmother used to walk around softly. But I could tell when she was coming. Basically, I would hear what seemed to me a lack of noise approaching; there was a lot of ambient noise from the living room (the windows were open which means lots of trees, birds, wind, etc. to hear), so someone walking down the hallway towards my room from the living room seemingly blocked some of the sound. It was very slight, but it was enough so I would usually be looking up at my grandma when she turned the corner to my room. I've had other experiences, like hearing if someone was sticking their hand in front of my face when I was blindfolded (it had to be in a fairly quiet room however).
Sigh, I miss having my good hearing. 25 years and lots of concerts, New years festivals and 4th of Julys will do that. It would be so helpful now to have that hearing, especially when my boss walks to my cubicle
0- Eamonman Proud member of DNRC
When capacitors are charged and drained quickly, they can emit sound. As the charge changes, the two plates that hold the charge will try and move closer or further apart, in a similar way to a speaker. Unlike SRAM, DRAM is actually made from banks of tiny capacitors. In older machines, you could often hear the memory singing while the bootup memory check was in progress.
While you can't hear a bit changing here and there, when changing large amounts of memory very quickly, such as changing/redrawing a screen, the sound soon mounts up, and you can hear it.
--[me]
When you do stuff, the CPU draws more current. This could affect all the chokes and stuff in the power supply. Small chopper PSUs such as those used to regulate down the 5v/3.3v rail to the 1.5~odd volts that modern CPUs need have several inductors, which could vibrate and make noises. Especially when attached to a big wobbly fibreglass sounding board.
Properly designed hardware should not do this.
A few weeks ago, I thought my Soyo Dragon motherboard had gone flaky because I was getting massive fs corruption when copying between drives. I panicked and went out and bought a new motherboard without having done any research. I told the guy I wanted to replace a Soyo Dragon and had 5 IDE devices, including 3 7200 RPM drives. The moron gave me an MSI KT3 Ultra2. That is not a replacement for a Dragon. The onboard sound doesn't even have digital audio outputs. I was using the Dragon's SPDIF to connect to my speakers. It sounds very nice.
I tried it out anyway. One thing I noticed right away was that I could hear noise whenever I selected text or moved a window. I took it back (for other reasons as well) and got my money back. The fs corruption was caused by the power supply unable to put out the power so I got a new one.
Right now I'm using the Dragon's analog out and there's no noise at all at any normal volume. If I turn everything up to maximum, I can barely hear something above the fan noise, but if I play something at that level, my ears would hurt.
Plugging in your monitor to your PC turns it's cable into a giant antennae. Just like TEMPEST. When a bunch of changes are made on screen the signal going to the monitor fluxuates dramatically. This fluctuaion is picked up by the antennae that is your speaker leads.
RF shielding and those magnetic cylinders on the cable help to reduce this.
However you still have an energized cable with radiply changing frequencies flowing across it. And those frequencies radiate and are picked up by other antennae and transmitted along their length.
Have fun sometime and put your cellphone next to a boombox with the volumed cranked up on a dead source. Then call the phone and listen to the funkiness.
One good thing about music... when it hits you, you feel no pain. So hit me with music. -Bob Marley
I have the same problem with my LCD iMac. It's not attributable to simple CPU usage, but rather the interface. When I drag windows, move scroll bars, access menus, etc., I hear a slight grinding sound (sort of like a hard drive but considerably quieter).
Then again, when I've got iTunes blaring it doesn't really matter.
Gabriel Ricard
On that laptop there's a power inverter board right near the back of the unit, near the built-in speakers. If that unit is not performing correctly then the power change needed to actually change the million pixels on the LCD will cause a fluctuation in the EMF it emits. Being so close to the BUILT-IN speakers, you'll likely hear the buzz there even if the sound is turned off as the EMF itself is driving the speakers.
Does the sound change when the brightness is turned down? If the above is right, then the sound will not be as loud when the brightness is turned to one notch above off.
My vote is for the RF noise being picked up by the unshielded soundcard. Just think --- the companies making the cards are constantly trying to find ways to make them cheaper. I mean, just how far can they go adding new features before the average person can't tell the difference anymore. The only thing left at that point is to find ways to make your product more cheaply than any of your competitors, and one way to do that is to not bother with the engineering involved in making an RF shielded card... "Hate my people? I love my people! PULL!"
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? ;-)
--
Evan
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
'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?
Since I haven't seen a cogent explanation posted yet, I'll take a swing.
Fact 1. 60 Hz transformer hum is unrelated to what you're hearing. (That would be at 120 Hz and relatively independent of screen refresh, which doesn't match your symptoms.) As a sidebar, 60 Hz hum is caused by the Lorentz force between the electric current in a transformer coil and the magnetic field that the current induces, which produces an radial outward force on the coil. (This effect is what limits the size of magnetic fields we can create in the laboratory -- no one wants an exploding electromagnet.) As the 60 Hz alternating current runs back and forth through the transformer, a 120 Hz mechanical vibration is induced.
Fact 2. It's also not directly related to "CRT whine". We can tell this because: (a) CRT whine is independent of whether screen contents are changing, and (b) CRT whine is a directly audible mechanical vibration, not a crosstalk into your audio out line. CRT whine is caused by the electronics that drive the electron gun's horizontal deflector. For example, if you scan 500 lines 60 times a second, the signal on the horizontal deflection plates is at 30 kHz, which some people can hear. Most modern computers have enough scan lines and a high enough refresh rate that the signal frequency is too high for anyone to hear, making this not a common problem with newer computers.
Fact 3. What you're hearing is caused by capacitive coupling between signal lines (wires) inside your computer. Because of the electric repulsion between electrons, high-frequency signals can "conduct" across the air between separate wires, especially if the wires are close together. In your case, it's crosstalk between the display and audio circuitry. This crosstalk interference can be reduced with grounded metal RF shielding, but it adds cost/bulk/weight and so manufacturers try to minimize the amount they use. An audio company would shield the DAC and preamp components carefully to bring the noise below a perceptible level; a typical computer manufacturer will just make it sound ok for ordinary use.
My guess... ...is that you have an active-matrix LCD screen, not a passive LCD or CRT. The reason is that you only hear the noise when the screen content changes. Unlike the other two, an active-matrix screen has transistors at each pixel that remember their state. Thus there is a drive signal to the screen only when pixels are changing. Only if relatively large portions of the LCD are being continually rewritten will the duty cycle of this drive signal be substantial, and therefore the crosstalk be audible.
Conclusion: It's annoying, but there's not much you can do about it without buying a higher-quality (i.e., better-shielded) audio card.
My hearing isn't all that great - I think I've suffered damage from listening to music too loud in headphones and later playing in a few bands (the amps went up to 11!). It manifests itself as muddy hearing of words, though - I tend to snap to alertness at a small noise.
As a music lover, it's depressing. As someone who worked with the blind (DOS users might remember txt2b and txt2b2, text to grade 2 braille translators I wrote), I'd rather lose my sight than my hearing.
--
Evan
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
I'm amazed at the number of answers from the "Slashdot experts" and yet I don't see the correct one yet.
Yet you also fail to give a correct answer too.
Even though some claim they (dogs probably can) hear their video card HSync signal, most of the time what you hear when the speakers are off is static electricity discharges like when you degauss your monitor.
On the other hand the sounds the original poster refers to are most probably caused by the induced voltages in the speakers from **changes** in the nearby electromagnetic fields emanating from the front and back of monitors (especially the cheap ones with crappy farady cages), as the screen content and colors change. Conditions that maximize this would be high contrast patterns, like alternating bands of bright and dark, since those cause more change in the electromagnetic field, which maximizes inductions in nearby conductors, like the coils fo your speakers.
On several computers I have noticed sounds (it's a clicking or thumping sound) that occur when the mouse is moved, proportional to how fast it is moving. Does the sound only occur when moving a large window, or does mousing while the window (or similar screen content, e.g. white background etc.) is visible?
Caveat Emptor is not a business model.
What exactly is it you do for a living?! Do you hear these silent alarms often?
He said he's 100% Irish. I think that's explanation enough.
Any more of these probing questions and we'll probably be seeing your name in the papers, and I don't mean the funnies.