[mythtv-users] HD-PVR horizontal bands

[Greg Oliver]

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)...