[linux-audio-user] noise from soundcard

Mark Knecht mknecht at controlnet.com
Thu Oct 16 18:06:45 EDT 2003

> This is a little off-topic, but I hope you don't mind.  I get quite a
> lot of noise from my soundcard.  There is a pulsing that sounds
> something like a very fast morse code at a consistent pitch, and it's
> unacceptably loud.  I notice variations in this noise based on how I
> move my mouse.
> At first I thought this was just because of my shoddy 5-year-old
> Soundblaster Live, but I have a new Audiophile 2496 and it does the same
> thing.
> Today I tried removing the stereo mini plug from my soundcard and
> touching it to the metal on my case.  The sound was nearly identical.
> >From the little that I know about electronics, I conclude that the
> problem is voltage fluctuations in the metal of the case.  Does this
> mean my case needs to be grounded somehow?
> What can I do to fix this problem?
> Josh

   Not at all sure about the case grounding part. That's pretty strange.
Maybe your external speakers and your PC are on different power grounds?
Watch out if either is 2-prong. People get killed in the US every year due
to our unsafe power system.

   The mouse part of this is a great example of what happens in some systems
when the sound card IRQ is 'behind' the mouse IRQ, or possibly shared with
the mouse IRQ. The 'IRQ ordering' in a standard PCI (non-SMP, non-IOAPIC)


(sometimes the #8 is replace by the #2 - don't worry about that.)

Do an lspci to see what IRQ's you mouse and sound card have.

The reason you'd get a noise when you move you mouse is that the mouse
interrupt handler is called, it takes time, and that delays the sound card
doing it's work. This delay empties a buffer or something and that causes a

A consistent sound could be some other device, like a disk drive, creating
interrupts and your sound card being on a bad IRQ.

If you put a sound blaster on IRQ 5, 6 or, then in my experience I have had
a lot of problems.

This could all be correct and solve your problems, or it could have nothing
to do with your system. ;-)

Hope this helps,

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