Audio loopback in linux kernel?

[Robert Olson]

>When line is non-zero, I can still hear myself, but when I set it
>to zero, there's no evidence that I'm transmitting anything. Does that
>make sense?

It does. The Crystal audio gear you've got may be AC97 compliant. AC97 
specifies among other things the on-board mixer configuration. (see 
http://www.ece.utexas.edu/~kettler/lecture2/sld040.htm for a block 
diagram). In this mixer, the line level adjustment only changes the level 
of the path from line in to line out. Capture gain is adjusted with the 
Input Gain adjustment on the mixer. This shows up as the igain control on 
the OSS mixer.

Unfortunately, I don't think that rat is using that as the line in gain 
selector in the app. The workaround would be to run a separate mixer app 
and use that to control gains. This is something that the ALSA rat knows 
about and compensates for ...

>Interestingly, rat resets line when I start to transmit, so I
>have to reset it, but in any case the whole system doesn't seem to work
>with this sound card. We've just ordered the Soundblaster PCI/128 card -
>hopefully it will arrive sometime this week. (Do you realize that that
>card is becoming hard to find?)


Yup. An alternative is the Creative Ensoniq AudioPCI. However, I think this 
is also an AC97 card, so it may have the same problems the crystal card.

--bob
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