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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?"
I hear noises too... but my doctor solved that problem :-)
But seriously, could the monitor cable be near a power cable or speaker cable? I can hear interference whenever the two are nearby.
Can you hear the noise even if speakers are not connected or nearby?
Maybe this page (see the section "noise interference") may help: http://www.smmpa.org/atwork/pwrqual.html
that might be true if it were a crt, but it's an lcd. there are no electrons hitting anything, just crystals interacting with light.
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
...When you're 40, you won't hear it anymore. Young ears hear much higher-pitched noises than old fogie ears.
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
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.
You can DEFINITELY hear sounds of this nature (during screen redraw) come out of the speakers of many older computers. I had this issue with my Amiga.
If the noise is actually originating in the video card, it's probably due to poor design in terms of RF, and the noise is probably being put out onto the ground of the motherboard, and thus transmitted to the sound card.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"