[mythtv-users] tuning two-card systems ?

Phill Wiggin wigginp at mantech-wva.com
Tue Oct 19 15:04:17 UTC 2004

Adam Felson wrote:

>>I just managed to build my two-card (bttv cards!) system.  It works
>>fine I guess, when recording two channels it is 0% idle, but still
>>everything appears to get to disk just fine for now.  I've seen no
>>jerking or hiccups or artifacts.  More on that setup below. First my
>You're still misreading your cpu useage.  There's *absolutely* no way
>you're running two cards with no cpu useage.  
Oh for crimeny's sake. Actually _read_ his post:

"when recording two channels it is 0% idle"

Not 0% CPU usage.   He's saying the CPU is pegged at 100% usage.

>Impossible.  Absolutely.
>When I ran two cards on an Athlon XP 3000, I typically got 30% useage
>for the card processes alone and another 25% per transcode process.  If
>I did mpeg4 encoding in real time, I got 30%/card.
>Nowadays I'm running two pvr-250s an one bttv (bt878) card.
>>I notice that my two bttv cards are not what you'd call exactly in
>>sync, where the tuners are concerned.  If one card gives good picture,
>>the other is just slightly off-channel so the colors are too
>>pronounced, or I get stripes and other interference.  Now what I wonder
>>is this, can one finetune channels per-card, or is the channel
>>frequency globally defined for all cards ?
>I've never had color problems.  Perhaps you have a defective card or are
>running an old version of video4linux.
I suppose the card could be defective, but there are quite a few 
alternatives.  If the cards aren't the same make/model, you might have 
an incorrect tuner associated with it. The signal might be screwy 
(pardon my lack of technical jargon here.. I don't know that much about 
cable signals).  Personally, my problems with my bttv card were a 
combination of an incorrect "tuner=" line in my module configuration and 
a crappy old cable.  Once I fixed the "tuner=" line and replaced the 
cable, my bttv card worked fine.

>You shouldn't need per/card finetuning as they're receiving the same
>signal.  Spend the $35 and replace the defective card.
A person very well could use per card finetuning.  If the cards aren't 
the same make/model, one or the other might need tweaking. 

As to spending "the $35" to replace the card... If your time is worth 
more than that $35, that might be a viable option.  But, if you enjoy 
tooling with the hardware, you could always try removing the card that's 
"working" and see if you can get the other card working correctly by 

I don't know whether you can finetune an entire card, but you could try 
to mess with the 'finetune' values on a per-channel basis. (I'm 
currently looking at it in the webmin interface, but I believe it's 
accessible through mythtv-setup.)

Good luck!

--Phill W.

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