Subject: Re: noise on pci bus?
To: None < (rfc822 Compliance issue To>
From: Brian Rose <>
List: current-users
Date: 01/17/2005 10:32:04
Sean Davis wrote:

> I have no idea what's causing this, but I'm experiencing what I can best
> describe as "noise" coming over the PCI bus. At least, that's my guess. For
> example, it's happening under the following circumstances:
> root is on wd0a (SATA, onboard viaide)
> anoncvs mirror is on wd1a (SATA, onboard viaide)
> music is on wd2a (ATA100, onboard viaide)
> sound card is a PCI SB Live! 5.1. I have an onboard auvia, but for various
> reasons (such as support for it being even worse than support for emuxki), I
> don't use it.
> When I was playing .flac's from a directory on wd2a, and did an rm -rf of
> the anoncvs mirror, the music started getting distorted. Not skipping, but
> getting staticy.
> Any ideas?

The noise is probably coming through the power pins on the bus. Most 
inexpensive sound cards do not have discrete amplifiers and do not 
adequately filter the incoming power from the PCI bus. As a result, you get 
distorted sound. I have one machine that does that and you can "hear" what 
the computer is doing by the chirps and tones coming through the sound card.

The best way to solve this is to get a better sound card. Look for a lot of 
electrolytic caps (little "trash cans") on the board. Some of the _really_ 
nice boards pull their power from the power supply and not the PCI bus 
power rails.

The cheaper boards do not have this because they integrate everything into 
an IC to cut down on costs. Since the amplifier is inside the chip, there 
isn't a reliable way to improve the situation. If you are adventurous, you 
could try placing a capacitor between the power and ground rails on the 
card. This will smooth out the sound card's power supply, which should 
improve the situation a bit. But noise generated inside the chip itself 
will likely leak onto the line.

Onboard sound cards _might_ be better, but probably not. A good amplifier 
section simply takes up too much board space and very few motherboards are 
sold for the qualify of their sound.

Also, If you have a digital outputs, use those.