[mythtv-users] Re: HDTV digital static with DVB

[ffrr]

sean.walsh at agincourtgroup.com.au wrote:

>
> > I chased video glitches from my DVB setup for ages, and with a lot of
> > help from the list, I finally nailed it. It was the Si 3112 SATA
> > controller chip doing nasties on the PCI bus and corrupting the mpeg
> > stream from the DVB card.
> >
>
> I've recently had a similar issue migrating to FC4 and a new 300gb SATA
> drive.  I was getting the same "poor reception"
> on DVB when the SATA drive was working hard. I was able to confirm 
> that it
> was the SATA drive alone through experimentation under my prior FC3 
> set-up.
>
> My motherboard (gigabyte GA-K8NS Pro) has two pairs of SATA connectors 
> - one
> pair near the edge of the card (and adjacent the outer most PCI slots -
> where my DVB cards are) and another pair near the CPU socket.  The 
> pairs use
> different SATA controllers - one a Sil3512 and the other nVIDIA 
> nForce3 250.
>
> I observed a vast improvement just by swapping to the pair furthest 
> from the
> DVB cards (nForce3).  I still get occasional interference artefacts at 
> times
> of high IO - but I'm hoping to play with shielding to resolve this. The 2
> controllers are pretty much right next to each other but the Sil3512
> controller that serves the outside pair is also a little closer to the 
> DVB
> cards slots.  I don't know whether proximity to the DVB cards or the 
> chipset
> is to blame for the interference.
>
> Does anyone have any suggestions for effective shielding of either the 
> cards
> for the SATA controller/cables?

That's not going to be easy to do.  

But one question here first.  If there's so much
electronic noise coming from the SATA controller/cables/disks, why don't 
we hear it in
the audio?  That's usually the first thing to suffer in an electrically 
noisy environment.

You say that it is a lot better when you use the nForce controller.  
Well given that the
early Si 3112 chip was so bad it even corrupted file systems, I can 
believe your later
one is still inferior to the nForce chip.  I guess I am saying it might 
be a better engineered
chip that's producing the improvement, not proximity to the DVB card, 
and that it might not be
electrical interference, but the way it uses the pci bus.

This is not unheard of.  I remember early graphics cards, under Windows, 
would cause
audio glitches when scrolling the screen (as in scolling a web page 
under IE) because
the drivers were tweaked to give good benchmarks.  In fact, they didn't 
obey all the 'road
rules' on the pci bus, and jumped all over other card's useage of it.  
It made them run faster though :-)