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?"

Comments

Re:Wow!!!!

[drinkypoo]

I think you're probably wrong. I think it's far more likely that the sounds being heard are related to the power supply of the monitor. We all know that monitors make a number of sounds during normal operation and that they have a lot of high voltage inside of them.

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.