[mythtv-users] HD-PVR horizontal bands

[Christopher Meredith]

On Wed, Nov 17, 2010 at 2:56 PM, Greg Oliver <oliver.greg at gmail.com> wrote:

> On Wed, Nov 17, 2010 at 2:46 PM, Christopher Meredith
> <chmeredith at gmail.com> wrote:
> > On Wed, Nov 17, 2010 at 2:00 PM, Greg <greg12866 at nycap.rr.com> wrote:
> >>
> >> On 11/17/2010 12:20 PM, Brian Wood wrote:
> >>>
> >>> 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
> >>>> fashion.
> >>>
> >>> 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.
> >
> > Thanks all for the good suggestions. I think I am going to experiment
> with
> > the cable more. The first one I was using was the one Comcast gave me
> with
> > the STB (because it was already connected). Then I replaced it with the
> one
> > that came with the HD-PVR, since I assumed that would be best suited for
> the
> > device (since they included it, and all).
> >
> > Interestingly, I have had this same problem with two different STBs
> (first
> > was the SA3250HD, second is a Cisco RNG-150). I think I'll see if I can
> find
> > a higher quality, shorter component cable, and if that doesn't work, look
> > into the ground loop isolator. As a side note, aren't there devices that
> can
> > be clipped on to an existing cable? I seem to recall seeing these
> somewhere.
>
> Yeah, you can get magnetic ferrules for the cables, but if your hdpvr
> came with the same cables mine did (the 5 wire joined cable), it is
> very high quality (at least mine is)...
>
>
Yeah, that's the one I'm using. I wonder what the problem is, then...
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