[mythtv-users] HD-PVR horizontal bands
Greg
greg12866 at nycap.rr.com
Wed Nov 17 21:28:34 UTC 2010
On 11/17/2010 03:46 PM, Christopher Meredith wrote:
> On Wed, Nov 17, 2010 at 2:00 PM, Greg <greg12866 at nycap.rr.com
> <mailto: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 <mailto: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.
>
>
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I think you are thinking about a toroidal coil..Simple to make if you
have the parts...
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