LinuxMusicians

Posted: **Tue Dec 29, 2015 9:22 am**

I am trying to figure out how to configure the alsa snd_aloop module.

I am currently using kxstudio cadence with their alsa->loop->jack plugin which works pretty well but on my laptop it seems my recorder is very close to my speakers so if I try to play audio through the built in speakers and record at the same time I get terrible feedback. I am going to buy a simple usb mic to use but I am having some trouble figuring it out how to use the snd_loop.

here's my device aplay -l

**** List of PLAYBACK Hardware Devices ****
card 0: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
Subdevices: 7/8
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: 7/8
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: 0/1
Subdevice #0: subdevice #0
card 2: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0

this is the .asoundrc file that I am using.

Code: Select all

# ------------------------------------------------------
# Custom asoundrc file for use with snd-aloop and JACK
#
# use it like this:
# env JACK_SAMPLE_RATE=44100 JACK_PERIOD_SIZE=1024 alsa_in (...)
#

# ------------------------------------------------------
# playback device
pcm.aloopPlayback {
  type dmix
  ipc_key 1
  ipc_key_add_uid true
  slave {
    pcm "hw:Loopback,0,0"
    format S32_LE
    rate {
      @func igetenv
      vars [ JACK_SAMPLE_RATE ]
      default 44100
    }
    period_size {
      @func igetenv
      vars [ JACK_PERIOD_SIZE ]
      default 1024
    }
    buffer_size 4096
  }
}

# capture device
pcm.aloopCapture {
  type dsnoop
  ipc_key 2
  ipc_key_add_uid true
  slave {
    pcm "hw:Loopback,0,1"
    format S32_LE
    rate {
      @func igetenv
      vars [ JACK_SAMPLE_RATE ]
      default 44100
    }
    period_size {
      @func igetenv
      vars [ JACK_PERIOD_SIZE ]
      default 1024
    }
    buffer_size 4096
  }
}

# duplex device
pcm.aloopDuplex {
  type asym
  playback.pcm "aloopPlayback"
  capture.pcm "aloopCapture"
}

# ------------------------------------------------------
# default device
pcm.!default {
  type plug
  slave.pcm "aloopDuplex"
}

# ------------------------------------------------------
# alsa_in -j alsa_in -dcloop -q 1
pcm.cloop {
  type dsnoop
  ipc_key 3
  ipc_key_add_uid true
  slave {
    pcm "hw:Loopback,1,0"
    channels 2
    format S32_LE
    rate {
      @func igetenv
      vars [ JACK_SAMPLE_RATE ]
      default 44100
    }
    period_size {
      @func igetenv
      vars [ JACK_PERIOD_SIZE ]
      default 1024
    }
    buffer_size 32768
  }
}

# ------------------------------------------------------
# alsa_out -j alsa_out -dploop -q 1
pcm.ploop {
  type plug
  slave.pcm "hw:Loopback,1,1"
}

The thing that I don't really understand correctly is how do I use the other virtual links and how they work with the systems speakers and mic. If I can figure this out I might not even need the mic.

the loopbacks look like this:

Code: Select all

card 0: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
  Subdevices: 7/8
  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: 7/8
  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

so let's say I do

Code: Select all

aplay -o alsa plughw:0,1 track.wav

then the audio will be available to record from

Code: Select all

plughw:1,0

is that correct?

If that is correct then how can I connect the plughw:1,0 to my speakers?

Posted: **Tue Dec 29, 2015 11:06 pm**

I am not using the snd_aloop module but I think you are confused with the audio card numbering scheme.

hw:1,0 means card 1, device 0. In your case, card 1 is not the loopback card, but the onboard card.

In general, hw:x,y,z (or plughw:x,y,z, for that matter) means card x, device y, subdevice z. Subdevice number is not often needed and will default to #0 when you give only two numbers. Similarly, device will be #0 when you give only one number. For example, hw:1 defaults to hw:1,0 and this is also hw:1,0,0
Also, card number can be substituted by card name. For example, "hw:Loopback,1" is the device #1 of the Loopback card (the same as hw:0,1 in your case, as your card #0 is the Loopback card).
I also don't know the reason why you use plughw instead of just hw, but that's probably my inexperience with the loopback card.

To get a list of capture devices use "arecord -l". Many devices are duplex (they are able to capture and playback so they appear in
both lists "aplay -l" and "arecord-l") but you never know.

Cheers, Pablo

LinuxMusicians

alsa_loopback

alsa_loopback

Re: alsa_loopback