f13 pulse and passthrough

Ian Malone ibmalone at gmail.com
Tue Oct 12 21:38:51 UTC 2010


On 12 October 2010 15:34, Ian Malone <ibmalone at gmail.com> wrote:
> On 12 October 2010 14:16, Tim <ignored_mailbox at yahoo.com.au> wrote:
>> On Mon, 2010-10-11 at 23:16 +0100, Ian Malone wrote:
>>> Anyway the
>>> situation is this: I'd like to be able to play a guitar through my
>>> sound card and be able to listen to backing tracks and other things at
>>> the same time. The suggested "pacmd load-module module-loopback" isn't
>>> viable as it has latency. JackD works fine for guitar (and I can use
>>> things like rakarrack or guitarix which are good fun), but using JACK
>>> seems to mean I can't use other sound sources (presumably it connects
>>> to ALSA).
>>
>> I think you're going to have to clearly define what you mean by pass
>> through the audio, because you've brought up two very different things,
>> describing what you want to do, and what interests you.
>>
>> To me, that means sound going into an input socket, and the sound card's
>> audio mixer passing it through to the output, by turning up a monitor
>> fader.  This requires nothing more than to control the hardware mixer in
>> the sound card.  The various Gnome or KDE volume controls should be able
>> to do this for you, or alsamixer through the console.
>>
>
> That's precisely what I want to do. It no longer seems to happen,
> possibly this is something to do with my driver, but I've adjusted all
> the controls I can see through Gnome. I'll have a go at alsamixer.
>

Having investigated further, my card has a rather interesting set of
mixers when looked at in alsamixer, there are 8 hardware mixers, and
each can be mapped to PCM, h/w in0, h/w in1 IEC958 L and IEC958 R. The
result is that I can map the first two hardware mixers (stereo left
and right, the others are part of a 7.1 setup) to the PCM sound or to
the recording source, but not both.
Oddly I did find a control labelled AC 97 which appears to govern a
hardware monitor, though only on the left channel. I suppose it's a
start, might have to take it to the alsa list at this point.

>> To others, they might be thinking of inputting audio, processing it
>> through the computer, and outputting the end result (with or without any
>> effects).  This could be done through pulse, or JACK.  But would require
>> a system that could *play* your inputted audio at the same time as
>> playing your backing tracks.
>>
>
> I agree this is different. Being able to do effects processing at the
> same time is attractive, but that's a more complex scenario and I'd
> actually be happy with just being able to monitor the line in (as in
> your hardware mixer paragraph) and I can't see where to switch it on.
>

I got an off-list response to this effect. After installing
pulseaudio-module-jack with Yum, then starting Jack, it's possible to
do:
pacmd load-module module-jack-sink
pacmd load-module module-jack-source
(won't work unless Jack is running), and then use sound preferences to
select the Jack plugins as input and output for Pulse it's possible to
have Pulse outputting through Jack. Though this feels a bit
overcomplex unless you do want to be able to do effects processing.

-- 
imalone


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