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

Joseph A. Caputo jcaputo1 at comcast.net
Thu Mar 25 16:02:45 EST 2004


On Thursday 25 March 2004 15:27, Bruce Markey wrote:
> Peter Shipley wrote:
> > Interesting...I had forgot to load btaudio but the output is:
> >
> > $ modprobe btaudio
> > btaudio: driver version 0.7 loaded [digital+analog]
> > btaudio: Bt878 (rev 17) at 02:07.1, irq: 19, latency: 32, mmio:
> > 0xf6001000 btaudio: using card config "default"
> > btaudio: registered device dsp1 [digital]
> > btaudio: registered device dsp2 [analog]
> > btaudio: registered device mixer1
> >
> > So it would suggest that it is supported...
>
> Unfortunately, it doesn't. The module will always load with
> similar messages for any card but that mean that there is a
> DSP on the card or even if an existing DSP will produce any
> data with btaudio.
>
> > Got any ideas ? Not sure how this all fits together.
>
> 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.
>
> The differences are that the on-card DSP may have a fixed sample
> rate of 32000, it may be difficult to set the capture volume, and
> you can't replace the DSP if the quality is bad. Using a soundcard
> you can choose any sample rate, set the capture level with
> alsamixer and upgrade your soundcard at any time for any reason.
>
> I now see btaudio as a limitation to be avoided unless necessary
> and patching into a good sound card of your choice as the better
> approach.


Yes, but you're forgetting some important reasons for using btaudio:

- if your card supports it, it can make life a lot easier (no need to 
monkey around with sound card drivers, or play with mixer settings, 
muting & capture sources -- much less confusing for a newbie)

- it's the only way for some folks to handle multiple tuner cards 
without having a separate sound card for each tuner

- if the machine is backend-only, no need for a sound card at all


-JAC


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