[mythtv-users] PVR-500 picture quality
cbeerse at gmail.com
Sun Feb 7 15:52:15 UTC 2010
Joey Morris schreef:
> I'm new to MythTV, and I've installed a PVR-500 to capture standard
> def programming from my cable company. The picture quality of the
> captured streams appears to be slightly lower than what I see when I
> connect the cable directly to my standard def TV. This is true for the
> card's coax connection (connecting directly from the wall) and for its
> composite and S-Video connections (connecting from the cable box).
> I've made sure the recording resolution is 720x480, I've increased the
> bitrates to 7000/8000, I'm using a G210 card with VDPAU enabled, and
> I've tried using a signal amplifier. I think I may be maxing out my
> PVR-500's performance.
> The quality is certainly tolerable. Although I notice the difference
> when comparing them side-by-side, I'm not sure I would if I viewed the
> card's output in isolation. Is the slight drop in picture quality just
> the nature of analog capture? Those of you using the PVR-500s, do you
> just live with it so you can enjoy the numerous benefits of MythTV? Or
> are there other things I can try to make the picture quality match
> what I see when I connect the cable box directly to the TV? If I
> eventually move to HD, can I expect a similarly slight quality drop
> when using the component output to an HD-PVR?
With analog capture cards, there are 2 ways to look at the quality:
There is the analog quality and the digital quality.
Digital quality is easy to see as it mostly can be described as on/off:
There is singal or there is no signal. All pixels are there or some
pixels are missing. That is also the base of artefacts and such.
With analog signal, there are way more ways of signal quality.
First thing to keep in mind is the type of signal. Analog TV broadcast
(air or cable) is in about 400 till 900 MHz. Most computers operate at
this speed (or faster). Hence they also broadcast signals in this range.
So for your antenna/cable connection to the computer, be sure to use
very good quality, specially in the sheelding. Most connector cables
that you get for free with your vcr or such are relative poor in
quality. Best to create a new one with metal connectors and good quality
If there are still analog signal problems, you best have a look inside
the computer. If the card can be moved to an other connector, away from
other devices, better do so.
Then there is the wiring of stuff like sata-disks. Those also operate in
the 100MHz range. be sure they are away from your capture card.
If it is for your future, most HD signals enter your house digitally.
Hence, they work or they don't work. If they don't work, it can still be
an analog problem. In the end, these signals (specially DVB-T and DVB-C)
are still in the 100 MHz range. Hence good sheelding both inside and
outside the computer is needed.
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