Sound card noises on graphics card access

Thomas Schuerger schuerge at
Tue Jun 10 23:45:53 PDT 2003

> > I have the following problem with FreeBSD 4.7-STABLE (running XFree86
> > 4.2.0).
> >
> > Recently, my AGP graphics card (Matrox G200) stopped working (a hardware
> > defect), so I used a rather old PCI Mach64 card instead. I also have
> > a Soundblaster AWE 64 (ISA, using pcm) in my box.
> >
> > Now, whenever the PCI bus is accessed while the soundcard plays something 
> > (e.g.
> > by moving windows around or playing a movie), I can actually *hear* the 
> > bus
> > accesses in my loudspeakers (very short and frequent pauses and clicking
> > noises - several per second, which sounds rather strange).
> >
> > It was the same (but the noises where extremely rare) when my MGA 200 was 
> > still
> > working, but with the PCI card, it is really horrible.
> >
> > When using Win98, my system behaves normally (no strange noises can be
> > heard on graphics access).
> >
> > I figure this being a driver problem. What can I do about that? Are
> > there any parameters I may have forgotten to set?
> Had the same type of problem when I initially tried BeOS and FreeBSD after 
> living in the Win world.  Whenever I moved the mouse cursor the sound card 
> emitted a noise like a motorboat - even increased in frequency as the 
> cursor accelerated!
> I think it's likely the sound card is picking up changes in electrical 
> field from the old video card.  Separate the two within the case as much as 
> possible and see if that helps - when I did it here, it put the "motorboat" 
> in permanent drydock.  :)

It's not that the video card electrically influences the sound card
that way. The sound is actually also delayed a bit upon PCI bus
accesses (which could not happen if the audio signal was simply
influenced by induction, also, this would happen when using Windows,
too). It may be an interrupt problem or something else (some sort of
bus contention?).

Perhaps FreeBSD uses the same interrupts for both cards (remember one
is a PCI card and the other one is an ISA card) and Windows doesn't.


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