[mythtv-users] HD-PVR horizontal bands
beww at beww.org
Wed Nov 17 17:20:43 UTC 2010
On Wednesday, November 17, 2010 10:11:58 am Robert McNamara wrote:
> On Wed, Nov 17, 2010 at 9:09 AM, Christopher Meredith
> <chmeredith at gmail.com> wrote:
> > I've been noticing this for a while now and finally want to fix it.
> > I'm noticing that on any content captured by the HD-PVR, there is
> > a thick band of discoloration that slowly moves up or down the
> > screen. It's very faint, and the effect is usually just to make
> > the "banded" area a shade lighter. In complex or fast-moving
> > scenes, it's virtually indiscernible. But you can definitely see
> > it in slow pans or dark scenes. I've tried using a different
> > component cable but it still happens.
> > Does anyone have suggestions about resolving this?
> It's good that you tried a different cable as that would have been my
> first suggestion. I don't see anything like this, and given you've
> tried another cable, my next inclination would be to say try
> capturing off of a totally different piece of hardware (ie, a DVD
> player, XBox 360, whatever) and see if things are different. My
> thought is that your current STB and the HD-PVR disagree in some
With NTSC, 60Hz. "hum" will show up as a single or double bar moving
slowly up through the screen (because the NTSC field rate is not quite
the 60Hz. of the power mains).
If you replaced the cable with an identical one, it might not have
helped. You might try one with better shielding.
But the problem may be that all your grounds (earths) are not at the
same potential, and what you are seeing is AC hum, the amount and
direction would vary with the frame/field rate of the video and the
frequency of your AC power (50 or 60 Hz.).
Grounding is a very complicated issue, and simply grounding everything
is site is usually not the best solution, as you get multiple paths and
varying potentials all over the place.
The best treatment of grounding issues I have seen is in Tremaine's
"Audio Cyclopedia", but that section is hundreds pf pages long.
But I suspect your problem is either induced signals due to bad cabling,
or "common mode" problems due to poor grounding.
More information about the mythtv-users