Re: [Jack-Devel] routing alsa through jack

Le Wed, 18 Dec 2013 05:24:37 +0100,
Lucio Crusca <[hidden]> a écrit :

> In data martedì 17 dicembre 2013 20:53:26, hai scritto:
> > Entirely appropriate. That approach works just fine here with older
> > versions of skype that support plain ALSA (I think newer versions of
> > skype are pulse only, but I don't know. 
> 
> AFAICT Skype 4 supports both Pulse and Alsa.
> 
> > Did you find
> > http://alsa.opensrc.org/Jack_and_Loopback_device_as_Alsa-to-Jack_bridge
> > ? It's somewhat verbose, but a very nice article with complete
> > step-by-step instructions and background information.
> 
> Yes, I did find it, but it's quite focused on a different target than
> simply routing audio through Jack with a single sound card, and I
> couldn't manage to distinguish the parts to be ignored in my case.
I think no part must be ignored. This article is about routing JACK and
ALSA together.

> When I finished doing what's written there, I was stuck with no audio
> at all, be it Alsa or Jack. I must have done something wrong, but I
> can't tell what because I wasn't understanding most of the things I
> was doing.
> 
> > Long story short: You cannot write directly to the loop-hardware
> > once alsa_in/out are connected. 
> 
> I'd say "oviously" here, except I didn't realize it myself... I think
> I took the opposite for granted because snd_aloop creates two
> soundcards, so I assumed I could lock one with Jack and the other
> with Alsa.
> 
> > asoundrc: http://robin.linuxaudio.org/tmp/asoundrc-loopback
> 
> Ok, I don't want to make the loop be the default device, for the time
> being: this way if something goes wrong i can just stop jackd and
> everything keeps working through Alsa. Should I avoid or change
> the last part ("pcm.!default") of that asoundrc then?

The ALSA programs are using the first available device as their
default device. The advantage using it for the loop device is the ALSA
programs will use the loop as device by default, and you will
automatically get the sound into JACK. The disadvantage is your will
have jack running all the time.

If, without snd_loopback, you can have the sound in ALSA, you must be
able to have it in JACK. The only difference with snd_loopback and the
zita bridges is you can route ALSA and JACK together and use both at
the same time. The sound card order is up to you, but if your main
usage is not audio pro but desktop use, it is much simpler to use the
loopback as first card, so the ALSA programs will use it by default.

Also, the zita bridges will give you a better sound quality than
alsa_in(out).

I use the following script (in ~/bin/loop2jack):

# Usage: loop2jack sample_rate frame/period
# where sample_rate is JACK sampling rate
# and frame/period is jack Frame/Period size
# To launch it from qjackctl:
# loop2jack %r %p

PSize=$(( $2/2 ))

# create the loop ALSA <-> JACK
/usr/bin/zita-j2a -d hw:0,1 -r $1 -p $PSize -L 2>&1 1> /dev/null &
/usr/bin/zita-a2j -d hw:0,1 -r $1 -p $PSize -L 2>&1 1> /dev/null &

# wait 1 second
sleep 1

# cloop ports -> jack output ports 
jack_connect zita-a2j:capture_1 system:playback_1
jack_connect zita-a2j:capture_2 system:playback_2


# jack input ports -> ploop ports
jack_connect system:capture_1 zita-j2a:playback_1
jack_connect system:capture_2 zita-j2a:playback_2


To launch it from qujackctl, the command to use is into the first
comment. Just put it into Options -> Execute script after Startup.

My ~/.asoundrc is as follow:
# playback PCM device: using loopback subdevice 0,0
pcm.amix {
  type dmix
  ipc_key 219345
  slave.pcm "hw:Loopback,0,0"
}

# soft volume
pcm.asoftvol {
  type softvol
  slave.pcm "amix"
  
  control { name PCM }
  
  min_dB -51.0
  max_dB   0.0
}

# capture PCM device: using loopback subdevice 0,1
pcm.asnoop {
  type dsnoop
  ipc_key 219346
  slave.pcm "hw:Loopback,0,1"
}

# duplex device combining our PCM devices defined above
pcm.aduplex {
  type asym
  playback.pcm "asoftvol"
  capture.pcm "asnoop"
}

# ------------------------------------------------------
# for jack alsa_in and alsa_out: looped-back signal at other ends
pcm.ploop {
  type plug
  slave.pcm "hw:Loopback,1,1"
}

pcm.cloop {
  type dsnoop
  ipc_key 219348
  slave.pcm "hw:Loopback,1,0"
}

# ------------------------------------------------------
# default device

pcm.!default {
  type plug
  slave.pcm "aduplex"
}


Cheers,
Dominique

> 
> > 
> >  zita-a2j -L -d hw:Loopback,1,0 -j cloop -n 2 -p 256
> >  zita-j2a -L -d hw:Loopback,1,1 -j ploop -n 2 -p 256
> >  sleep 1
> >  jack_connect cloop:capture_1 system:playback_1 &>/dev/null
> >  jack_connect cloop:capture_2 system:playback_2 &>/dev/null
> >  jack_connect system:capture_1 ploop:playback_1 &>/dev/null
> >  jack_connect system:capture_2 ploop:playback_2 &>/dev/null
> 
> I assume I could also make connections through the patchbay in
> qjackctl instead of using jack_connect, right? It's a more
> trial-and-error friendly method for the beginners...
> 
> 
> 
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