[mythtv-users] Picture Quality...

Brian Wood beww at beww.org
Mon Oct 9 22:15:15 UTC 2006

On Oct 9, 2006, at 3:49 PM, David Brodbeck wrote:

> Brian Wood wrote:
>> TV tuners are pretty much commodity items these days, and whether
>> they are going into TV sets or tuner cards they are essentially the
>> same thing. I haven't seen any real difference between them.
> I've found that TV tuner cards, living as they do inside an  
> electrically
> noisy computer, often have one or two channels where the picture is  
> poor
> compared to a TV set due to interference.  On other channels  
> they'll be
> fine.  Also, maybe because of this noise pick-up problem, tuner cards
> often seem to have less gain than a regular TV or VCR.  With a good
> cable signal you won't notice, but if the signal is a bit weak the
> picture from the card won't look as good.  I had one card for a while
> where the manual actually recommended using an external pre-amp.

There's no doubt that the inside of a typical PC is an incredibly  
hostile electrical environment. The DC power busses can be pretty  
crappy as well.

I had a frame-grabber card a few years back that had all kinds of  
noise in the output, I was able to improve things a lot by simply  
soldering the press-on metal lid of the tuner shield can at several  

As for pre-amps, there are many situations where using one,  
especially a cheap one, can make things worse not better. A tuner  
driven with too much signal on many channels can cause all sorts of  
intermod beats and that sort of thing.

It would be nice if the manufacturers simply told you what the  
optimum input level was, but OTOH not too many users are going to  
have a signal level meter to check that with.

Considering that a truly high-quality demodulator, like a Tektronix  
or a Rhode and Schwartz, costs over $20,000, I guess we can't  
complain too much about the performance of a $99 card:-)

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