G35: crosstalk from integrated GPU to sound chip

[Rainer Dorsch]

Am Sonntag, 8. Juni 2008 schrieben Sie:
> On Sunday, 8 June 2008 15:25:32 Rainer Dorsch wrote:
> > Hello,
> >
> > I am running Debian lenny on a G35 chipset (ASUS P5E-VM HDMI) and I
> > observed that the sound chip (?) picks crosstalk from the integrated GPU.
> >
> > It continously picks some noise. When one or several blocks of the screen
> > change, I can hear a "clack" sound. Also when I run glxgears the noise
> > level increases significantly.
> >
> > The noise does not change when I plug off the DVI/HDMI cable at the
> > computer or when I use a headset instead of the speakers. Thus I think
> > the crosstalk happens inside the system. The glxgears setup indicates
> > that it has something todo with the integrated GPU.
> >
> > Anybody seen something like this before?
> >
> > Any suggestions are welcome.
>
> I guess this is normal _if_ your sound card supports so
> called analog loopback (= you hear what is on its inputs)
> and you set input gain to maximum.
>
> If I do so, I can hear lots of things, like moving a mouse, running
> infinite loop on CPU, accessing hard disk, etc...
>
> I guess that everything is connected via ground, thus some small crosstalk
> is normal.
>
> I have seen this on several PCs

Good hint, thanks.

kmixer shows me a "Front Mic" and a "Front Mic Boost". They heavily influence 
this stange noise. Switching them off eliminates them.

Thanks,
Rainer

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Rainer Dorsch
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