Re: [gentoo-user] Problem with xf86-video-ati & nvidia-drivers

[meino.cramer@gmx.de]

Grant <emailgrant@gmail.com> [11-07-13 03:13]:
> >>> When I was using an Nvidia video card, I noticed a strange sort of
> >>> fuzzy edge effect if I used nvidia-drivers.  xf86-video-nouveau didn't
> >>> have the same problem.  Now I've switched to an ATI video card and
> >>> unfortunately I have the same problem with xf86-video-ati.  I tried to
> >>> enable the new modesetting radeon driver in the kernel to see if that
> >>> would help but it doesn't work with my HD4250 card yet.  Does anyone
> >>> know how to fix this?  Here's a photo of the effect around the mouse
> >>> cursor:
> >>>
> >>> http://imageshack.us/photo/my-images/804/cursor.jpg
> >>>
> >>> - Grant
> >>>
> >>
> >> Hi Grant,
> >>
> >> just a shot in the dark:
> >> The image looks to me as thos would be an analog instead of
> >> an digital problem.
> >> May be both propietary drivers switch to the highest possible
> >> data transfer rate and this triggers the problem.
> >> To check, whether this may be the problem:
> >> Instruct the driver to use either low resolution or low refresh
> >> rates. Check both.
> >> If the problem changes signifiently: Change the cables.
> >> May be only a pluf is not inserted correctly.
> >> Addtionally you can move the cables arround to see whether
> >> this will change the shadows around the cursor in any way...
> >>
> >> Good luck! :)
> >> Best regards
> >> mcc
> >
> > Thanks for that.  I'm still working on it but adding radeon.audio=0 to
> > grub cleaned it up about 75%.
> >
> > - Grant
> 
> It turns out the radeon.audio=0 setting disables HDMI data packets and
> puts the HDMI port in DVI mode.  mcc, I'm starting to think you had it
> pretty right on.  I've tried two different cables with the same result
> but I'm thinking this may be some sort of electrical interference
> issue.  I deal with stuff like that in audio.  There's a USB isolator
> which cleans the sound way up when used with a USB sound card:
> 
> http://www.analog.com/en/interface/digital-isolators/adum4160/products/product.html
> 
> Now I wish there was something like that for HDMI.
> 
> - Grant
> 

Hi Grant,

another shot into an even much deeper dark .... ;)

May be you have a problem here, which it is called "Brummschleife"
in german...sorry dont know the English equivalent...may be something
like "buzzing loop"...but this looks more like a strange translation 
made by google than by any other, human being ;)
Anyway....

A "Brummschleife" happens when doing something like this:

              +----+                          +-----------+
--------------+    |-(1)----------------------+ monitor or|-------------
mains         | PC |-(2)----------------------| amplifier |        mains         
--------------+    |    (audio/USB/video or   + or.....   |-------------
-+------------+----+     another low voltage  +-----------+-----------+-            
 |                       thingy)                                      |            
 (3)                                                                (4)
 |                                                                    |            
 _                                                                    _            
 ground                                                               ground       


 Normally all protective earth's connection should end in ONE point: A
 copper rod or someting like this.
 BUT often the wires between them are too long or there are two or
 even more end points. Result: HF from near by broadcast stations,
 60Hz mains frequency, ham radio station, microwave ovens and anything
 which can emit energy, pushes protective earth to another electrical
 potential than 0V.
 Since both, PC and -- in your case -- the monitor are using
 protective earth, they may be put on "another", may be even
 varying (over time) electrical potentials. Since they are connected 
 via a two-wire connection WITHOUT protective earth (no, the shielding 
 is not for that purpose) the difference in the potential earth put 
 both ends to different electrical reference points.
 This way you get an amplitude modulation of the signal between both
 endpoint. In case of 60HZ you will hear a "Brummschleife" sound on
 audio connection (a buzzing sound), in case of frequencies near 
 those of the video signal you will get "ghosts" in the monitor picture.

 Now, how to avoid that.
 Hit the one who have made the protective earth connection in your
 house.
 While you are searching for that person, you can try the following:
 Put all mains connectors of you PC rig into ONE wall connector
 with something like this (ok I miss some words here again and 
 since a picture says more than even thousands of /missing/ words
 here comes an image of what I mean:):
http://www.reichelt.de/Steckdosenleisten-ohne-Schalter/6-FACH-DOSE-WS-5/index.html?;ACTION=3;LA=2;ARTICLE=108651;GROUPID=4281;SID=11Thz@On8AAAIAABaBBrE9f5418078c2ea9fe6608e9765d978595

This way, all protective earth ends up in the same contact. No
differences in the electricla potential of the protective earth
anymore.

Why does the those USB-isolatore-like cables help here?

These small air core transformers (or in other words: There is
no core at all... ;) ) do a (german, sorry...)
"Gleichtaktunterdrueckung" which means, that any
potential difference (which is: the signal itsself) between
wire (1) and wire (2) is transmitted, and any modulating 
difference of electrical potential between (3) and (4),
influencing (1) and (2) at the same time the same way will
be suppressed by the transformers.


Hopefully the theorectical aspect of this will not surpress
the practical success here ;)

Good luck!
Best regards,
mcc