April 18, 2006

Curious George: My computer puts out some pretty annoying static on the audio line.

I've discovered that it has to do with the cable going from the motherboard to the front-panel audio connector, which is apparently picking up interference. Disconnecting it solves the problem, and I'll probably just use a splitter cable to get the same functionality. However... This is where it gets weird: certain actions on the computer will cause the static to cut out entirely. For example, scrolling in Opera. Scrolling graphics-heavy pages cause the static to cut out entirely, while text-only pages only cause it to stutter. Another, stranger, example is in Forte Agent, my email program. holding down the mouse button and moving it to the left edge of the screen causes the static to cease. Pressing the button down when the mouse is already at the edge doesn't. Neither does doing the same in other programs. All these effects are perfectly repeatable. My question: what's going on? What could be happening? Can I get it to happen all the time, to shut down the static? Should I just wrap the cable in tinfoil (and tape)? It is a (small) mystery. Anyone here know how to solve it?

posted by exppii 18 years ago
  • The only thing I can think of that those random actions might have in common would be spikes in CPU usage. One way to tell if this is the case (in Windows 2k/XP) would be to open up the task manager and watch the CPU usage on the performance tab. If you're playing other sound (e.g. music) at the same time, do you hear the music fine without the static when scrolling in Opera? Or does the music become choppy as well? As for why, that is one of the entirely weirdest computer idiosynchracies I've ever heard. It could be that a busy CPU is a less disruptive electromagnetic pattern in your case. Or else the tied up computer might be less likely to use some peripheral component on the motherboard which happens to be the one causing the disruption. I guess one useful thing to clarify would be where the sound is coming from. Do you only hear the static if other sound is playing, or is it constant? What if the PC is powered off? Do you hear the static when the OS is muted? What if the speakers are turned all the way down with their own "physical" volume control?
  • Bang on-- CPU usage is absolutely it. Other sound plays just fine, so causing CPU usage to spike like that does make it sound a little better. The mute button/master volume control has no effect on it. I guess this means I should start running SETI@home in the background, or something. As for when the PC is powered off, I'm going to bed now so I'll listen for it and tell you in the morning. Wacky li'l thing, ain't it? Now I have to figure out how to quiet down some of these fans, so as to enjoy my silence better.
  • My PC laptop is an absolute symphony of weird sounds. If I plug in a pair of headphones I can pick up exactly when it accesses my SD card reader, whenever the graphics board has to do some heavy processing, when the wireless port is doing something like scanning all channels, and if I insert a CD the sounds become overwhelming, discrete little beeps and whines, too. This is the case with every laptop I've owned, and also the desktop PC in the other room does something similar but not as interesting that seems to be bound to CPU usage and optical drive spinning. I thought this was just something everyone lived with with computer sound hardware, though maybe I could get a job like that blind guy who can diagnose telephone switchboard problems by listening to the clicks when you pick up a receiver.
  • "Should I just wrap the cable in tinfoil (and tape)?" That probly won't work & might short something. What this sounds like is ultra cheap components. Any electical device in use will give out radiation that interferes with audio signal, often varying with current etc. Normally audio cable is manufactured to beat this issue. You need a cable that is professional quality, with decent shielding. Buy a decent connector cable from the computer shop. If the problem persists, then the motherboard must be badly made. Get it replaced. I've never experienced this problem on any 'puter I've owned, & I work with extensive audio stuff on my PC, with & without a sound card. Make sure your cables do not touch one another. Make sure that audio cables do not come into proximity with power cables. Fields from a power cable can bleed easily into adjacent audio lines. If this problem continues, then maybe there's a bad solder or something on the motherboard or shitty component somewhere.
  • Only time I get static on my line is if I plug headphones in to my speaker jack. With most 'phones it isn't a problem, but using the iPod earbuds I need to turn the volume almost all the way off and I still get some background humming. It's weird.
  • The likely cause of this problem is poor grounding of the computer. Is it plugged directly into a three-prong wall outlet?
  • Motherboard is always poorly shielded. My comp does the same thing, but not quite as bad. Just changing the geometry of the cable might help, but You might also try carefully arranging some copper foil that is grounded to the case to shield the noisy parts. Just don't blame me if you short anything.