[proaudio] Re: [proaudio] Hello all! General linux daw question. Problems with x and h/drive events creating interference..

[Dominique Michel <dominique.michel@xxxxxxxxxxxx>]

Le Thu, 25 Jan 2007 09:43:54 +1300,
"independent commercial" <independentcommercial@xxxxxxxxx> a écrit :

> I think this is the first time I've posted here, so thank you all for your
> advice and especially to the devs who created this overlay.
> I am having problems with my amplifier amplifying noise from what seems to
> be activity on the PCI busses.
> First, a little bit of history.
> 
> I've been using this overlay for a little while and apart from
> underestimating my need for space on my /usr/ partition have had reasonably
> good luck with the setup. I have an A7m266 asus (AMD northbridge)
> motherboard with a Barton mobile cpu pin modded to 2Ghz. No problems there,
> runs well with cpuburn for some time. On the first slot is an LSI scsi card
> connected to 2 drives which have the root/swap and home partitions mounted
> on them respectively. Unfortunately no matter how much swapping around and
> fiddling in the scsi bios even though I am only using one channel and the
> other channel seems to be disabled, the second channel always takes a good
> IRQ. So, I've used that channel for the drives and the first, so-called
> disabled channel shares with the Matrox G550 card which drives a Dell
> 1920x1200 lcd monitor. Was the best I could do. The card has AGP 4x and
> FastWrites enabled in xorg. My kernel has the realtime-lsm module enabled
> and working, no preemtive RT patch. No problems there with xruns. The card
> is on the third slot and is an M-audio delta 66, it has it's on it's own IRQ
> of 9. There is nothing in the second slot. I realise if I moved the SCSI
> card to the second slot then the card wouldn't have to share with the AGP
> card but then it /always/ shares with the audio card which I figure is
> worse.
It is better if the sound card is on its own IRQ. As you are not using a
rt-kernel, you should be fine with shared IRQ with the graphic card from a
stability point of vue.

But the fact is at some graphic cards can be very noisy. And I think at
a shared IRQ on the graphic card will not help. I don't know the matrox driver,
but is it possible to completely disable the 3D hardware acceleration with it?
As example, with a nvidia card, you can use the nv 2D driver and it will spare
the IRQ as it is no 3D.

 Plus the actual SCSi channel sharing with the AGP card has nothing
> running on it (the drives are the channel which has it's own IRQ). I've read
> the d.robbins article on irqs but will have another look to see if there is
> anything I missed.
> 
The asus manual for your motherboard must show you which pci slots and
devices have shared IRQ.

> Here is the gripe and really is a strange one and I was hoping someone here
> might be able to point me to the right direction.
> Ok I am getting noise from x and drive events from the (admittedly average
> quality) amp, but not from my headphone amplifier which is connected to the
> other 2 channel outs on the card. Is it possible the amp is feeding back
> into the card through the rca cable to create these noise issues? I've
> swapped channels from the headphone amp and integrated amp on the audio card
> and still the same results.

Try another x driver, a general one. You will not get all the features of your
card, but it can help. Another test can be to use the in-board graphic card on
the motherboard. As long at you don't need hardware 3D, it will not be a big
difference between 2 different sound cards or drivers for a work as audio work,
but it can do a difference with the noise.

You have 2 sources of noise, the scsi and the graphics card, but as they are
shared the same IRQ, it can be very hard to diagnose the correct source of
noise. My guess is at it is the graphic card in combination with the shared IRQ.

If nothing help, you must consider a shield near the sound card, but be
careful. Put some pieces of hard paper or plastic between the shield and the
other hardwares, and don't cover a fan or something like that with the shield.

If the noise is coming from an input, jaaa can be useful to diagnose it. I
think at you already know at mixer as kmix are not reliable, so use something
as the alsamixer.

A last thing, you must be systematic, look at one thing after another.

Cheers,
Dominique