[mythtv-users] Getting sound from LiveTV through PCI bus

Bruce Markey bjm at lvcm.com
Fri Mar 26 00:54:35 EST 2004

Mike Jasper wrote:
> Bruce Markey wrote:
>> There is an unstated premise here that has tripped up many before
>> you. That is that if the analog to digital audio capture comes
>> from the TV card then that must be somehow better. I don't believe
>> this is true. Either the sound is digitized by a DSP on the TV card
>> or a DSP on a dedicated sound card. The analog signal travels for
>> miles from your cable head end and six more inches of wire isn't
>> going to kill the sound.
> If you have an analog signal (e.g., regular cable), how would you 
> deliver the audio to the sound card?

That is what the bttv card patch cable is for. The analog signal
from the coax frequency is passed thru over copper wire to the
soundcard. The analog signal that reaches the DSP on the soundcard
should be virtually the same as the analog signal that reaches
the DSP on a TV card that has one.

>  If you have digital cable you 
> could run a cable from the set top box audio-out to the sound card.

Exactly. There are actually two choices in that case. You can
plug directly into the sound card if the cable box is the only
input being used. Some people use both s-video from a settop
digital cable box and coax for regular cable. In that case, it
is better to connect the cable box audio into the line-in of the
TV card (apparently not all cards have a line-in) then use the
patch cable from the TV card to the soundcard. The reason for this
is that the TV card can switch the audio source when you change

> Or are you saying that by running a patch cable from the tuner card to 
> the sound card you'd bypass the tuner card's DSP and send the signal 
> straight to the sound card, where it is then digitized?

Correct. Not all (in fact, very few) bttv cards have a DSP
that can be used with btaudio. 

> ...I have two PVR-250's...

Well then this is all irrelevant to you because the PVR cards
do and must digitize on the card so that it is multiplexed in
the encoded audio and video stream that comes from the hardware
encoding card.

>  on an ASUS P4P800 mobo with an M-audio 
> Audiophile 2496 sound card.  I get really excellent audio with mythmusic 
> and mythvideo, but the audio from live tv or recorded shows has these 
> annoying artifacts.

In that case you should check out the IVTV site and mailing
list for more info. Your soundcard isn't used for recording but
only playback. If the soundcard doesn't have problems with playback
from other sources, the problem with recording may be the ivtv
driver or it's parameters.

--  bjm

More information about the mythtv-users mailing list