[mythtv-users] HD-PVR horizontal bands

[Christopher Meredith]

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.
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