mjhjmtu

I am having some trouble wrapping my head around the snd_aloop module.

I am trying to route all my audio through alsa without using pulseaudio. If I start jackd there's not sound from non alsa apps but things like rhythmbox or any other native jack supported software works just fine.

The main reason is that I do mostly audio editing but I listen to videos online as well.

I was reading that I can use the alsa snd_aloop module to setup virtual hw that I can route my non jack away apps audio through to get things to play nicely with jack via the alsa_in and alsa_out mechanism.

i've read quite a few tutorials like this one, this one looked over a lot of the documentation here and here as well.

The part that is most confusing to me is the loopback setup and the way alsa_in and alsa_out works.

For example with the snd_aloop module there's 2 devices with 8 subdevices

my aplay-l looks like this

**** List of PLAYBACK Hardware Devices ****
card 0: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
 Subdevices: 8/8
 Subdevice #0: subdevice #0
 Subdevice #1: subdevice #1
 Subdevice #2: subdevice #2
 Subdevice #3: subdevice #3
 Subdevice #4: subdevice #4
 Subdevice #5: subdevice #5
 Subdevice #6: subdevice #6
 Subdevice #7: subdevice #7
card 0: Loopback [Loopback], device 1: Loopback PCM [Loopback PCM]
 Subdevices: 8/8
 Subdevice #0: subdevice #0
 Subdevice #1: subdevice #1
 Subdevice #2: subdevice #2
 Subdevice #3: subdevice #3
 Subdevice #4: subdevice #4
 Subdevice #5: subdevice #5
 Subdevice #6: subdevice #6
 Subdevice #7: subdevice #7
card 1: PCH [HDA Intel PCH], device 0: CS4208 Analog [CS4208 Analog]
 Subdevices: 0/1
 Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 1: CS4208 Digital [CS4208 Digital]
 Subdevices: 1/1
 Subdevice #0: subdevice #0
card 2: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
 Subdevices: 1/1
 Subdevice #0: subdevice #0
card 2: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
 Subdevices: 1/1
 Subdevice #0: subdevice #0
card 2: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
 Subdevices: 1/1
 Subdevice #0: subdevice #0

if I try to setup my system like this:

#jack capture and playback
pcm.jack_capture_1 
 type plug
 slave.pcm "hw:Loopback,0,0"


pcm.jack_playback_1 
 type plug
 slave.pcm "hw:Loopback,0,1"


#alsa capture and playback
pcm.alsa_input_1 
 type plug
 slave.pcm "hw:Loopback,1,0"


pcm.alsa_output_1 
 type plug
 slave.pcm "hw:Loopback,1,1"



#playback devices
pcm.jack_audio_1 
 type asym
 playback.pcm "jack_playback_1"
 capture.pcm "jack_capture_1"

then do alsa_out -j "playback" -d jack_audio_1 sound.wav

I still get no output even after making the connections in the jack routing map.

My questions:
Looking at my setup I have the
loopback jack_capture_1 tied to hw:0,0
loopback jack_playback_1 tied to hw:0,1

that means any sound sent to jack_capture_1 should be echo out of jack_playback_1 is that correct?

also is the
alsa_in is the the alsa audio stream that'll go into the jack session while
alsa_out is the alsa audio stream that jack outputs after it finishes?

I have been reading everything that I can on the snd_aloop but even their official documentation seems a bit lacking.

Can someone help me sort this out?

A bit late with the answer but maybe someone finds this helpful ;)

/etc/modprobe.d/alsa.conf
alias snd-card-8 snd-aloop
options snd_aloop index=8 id=loop0 enable=1

/etc/asound.conf

#### Linrad #### 

pcm.loop0_0_0 
 type plug 
 slave 
 pcm "hw:loop0,0,0" 
 format FLOAT_LE 
 rate 96000 
 
 

pcm.linrad_alsa 
 type asym 
 playback.pcm "loop0_0_0" 
 capture.pcm "loop0_0_0" 
 hint 
 show on 
 description "Linrad: ALSA" 
 


pcm.loop0_1_0 
 type plug
 slave 
 pcm "hw:loop0,1,0"
 format FLOAT_LE
 rate 96000
 


pcm.linrad_jack 
 type asym
 playback.pcm "loop0_1_0"
 capture.pcm "loop0_1_0"
 hint 
 show on
 description "Linrad: JACK"
 


#### WSJTX ####

pcm.loop0_0_1 
 type plug
 slave 
 pcm "hw:loop0,0,1"
 format FLOAT_LE
 rate 96000
 


pcm.wsjtx_alsa 
 type asym
 playback.pcm "loop0_0_1"
 capture.pcm "loop0_0_1"
 hint 
 show on
 description "WSJTX: ALSA"
 


pcm.loop0_1_1 
 type plug
 slave 
 pcm "hw:loop0,1,1"
 format FLOAT_LE
 rate 96000
 


pcm.wsjtx_jack 
 type asym
 playback.pcm "loop0_1_1"
 capture.pcm "loop0_1_1"
 hint 
 show on
 description "WSJTX: JACK"
 


....

And for the piping to jack something like this (placed in a shell script that runs after jackd starts)

alsa_in -j "WSJTX source" -d wsjtx_jack -q 1 &> /dev/null &
alsa_out -j "WSJTX sink" -d wsjtx_jack -q 1 &> /dev/null &