[UFO Chicago] static on dsp when screen redraws?

[Neil R. Ormos]

On Fri, 4 Oct 2002, Peter A. Peterson II wrote:

> In the reinstall of flynn, I threw in my SBLive! card, and
> it works great, except when the screen is active. When I'm
> playing a video, or even when mozilla redraws -- like when
> a new page is loaded and the whole screen is redrawn --
> there is static on the dsp. It doesn't sound traditionally
> "choppy", it's sounds more like static. I should test to
> see if the static is present even when no sound is
> playing... that'd be useful to know.

> I wondered if maybe it was an IRQ-sharing issue, but the
> video card is on 9 and the sound card is on 10. The cards
> are also not directly next to each other, and moving the
> wires around in back doesn't seem to make a
> difference. (Like, moving the speaker wire away from the
> monitor cable.)

> You guys have any idea what the deal is with this? It's a
> dual-PII 333 -- it should be capable of playing a 300x400
> mpeg without choppy sound. Or much less, redrawing the
> screen without distorting oggs.

Have you tried to eliminate (analog) hardware issues as a
source of the problem?  You might start by plugging in a set
of non-amplified Walkman-type headphones to the sound card's
line out jack.  If the problem goes away, then it's probably
related to the speakers (well, more particularly, to the
power supply or amplifier associated with them), but there
could also be a ground loop or power supply issue on the
sound card.

You might also try making your sound software quiescent and
listening carefully to detect whether there's noise you can
correlate with system activity.  Also, are you sure the
static is correlated with video display activity, as opposed
to, say, disk activity?

Finally, you might carefully inspect the sound card to see
if there are any loose connections, cold solder joints or
broken PC trace.  The problem could be caused by a
disconnected bypass cap.

  --neil