snd-loopback does not work

[Sameguyy]

$pactl list short sources
80	alsa_output.platform-snd_aloop.0.analog-stereo.monitor	PipeWire	s32le 2ch 48000Hz	RUNNING
81	alsa_input.platform-snd_aloop.0.analog-stereo	PipeWire	s32le 2ch 48000Hz	RUNNING

These are two interfaces that Pipewire automatically pulled in, and the sound goes into 3.0 and doesn't leave from 3.1

That is, I play a sound on hw:3.0 and when I try to read something from hw:3.1 I get silence

aplay\arecord records silence
$ uname -r
6.17.8-arch1-1 Wayland PipeWire gnome

**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC892 Analog [ALC892 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 1: ALC892 Digital [ALC892 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: DACX6 [DAC-X6], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: DACX6 [DAC-X6], device 1: USB Audio [USB Audio #1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: NVidia [HDA NVidia], device 3: HDMI 0 [SAMSUNG]
  Subdevices: 0/1
  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
card 2: NVidia [HDA NVidia], device 9: HDMI 3 [HDMI 3]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 3: 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 3: 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

$pacman -Q | grep  alsa
alsa-card-profiles 1:1.4.9-1
alsa-lib 1.2.14-2
alsa-plugins 1:1.2.12-5
alsa-topology-conf 1.2.5.1-4
alsa-ucm-conf 1.2.14-2
alsa-utils 1.2.14-1
lib32-alsa-lib 1.2.14-2
lib32-alsa-plugins 1.2.12-1
vlc-plugin-alsa 3.0.21-31

[perexg]

You can check which substreams are used (and "cable" status) in /proc/asound/card3 tree (card3 should be the loopback card).

EDIT: Note that the full ALSA PCM device address is CARD,DEVICE,SUBDEVICE (three numbers). If subdevice is not specified, first available is used.