example camilladsp config for pi zero with two usb sound cards using alsa multi

85-my-usb-audio.rules

#The UGreen 80864 usb dongle uses the 32bit/384khz capable ALC4030 
#but changes product id depending on whats in the jack.
#this helps keep that name consistent. Future version may use serial number.

SUBSYSTEM!="sound", GOTO="my_usb_audio_end"

ACTION!="add", GOTO="my_usb_audio_end"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.1/1-1.1:1.0/sound/card?", ATTR{id}="Ugreen_CM"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.2/1-1.2:1.0/sound/card?", ATTR{id}="Ugreen_RT"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/sound/card?", ATTR{id}="Ugreen_RT"





LABEL="my_usb_audio_end"

SUBSYSTEM!="sound", GOTO="pa_naming_end"

ACTION!="change", GOTO="pa_naming_end"

KERNEL!="card*", GOTO="pa_naming_end"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.1/1-1.1:1.0/sound/card?", ENV{PULSE_NAME}="Ugreen_CM"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.2/1-1.2:1.0/sound/card?", ENV{PULSE_NAME}="Ugreen_RT"

DEVPATH=="/devices/platform/soc/20980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/sound/card?", ENV{PULSE_NAME}="Ugreen_RT"

LABEL="pa_naming_end"

active_config.yml

devices:
  adjust_period: 10
  capture:
    avoid_blocking_read: false
    channels: 2
    device: hw:Loopback,1,0
    format: S32LE
    retry_on_error: false
    type: Alsa
  capture_samplerate: 0
  chunksize: 1024
  enable_rate_adjust: false
  enable_resampling: false
  playback:
    channels: 4
    device: multicard
    format: S16LE
    type: Alsa
  queuelimit: 4
  resampler_type: BalancedAsync
  samplerate: 44100
  silence_threshold: 0
  silence_timeout: 0
  target_level: 0
filters:
  LR HP 4O:
    parameters:
      freq: 3000
      order: 4
      type: LinkwitzRileyHighpass
    type: BiquadCombo
  LR LP 4O:
    parameters:
      freq: 3000
      order: 4
      type: LinkwitzRileyLowpass
    type: BiquadCombo
  Tweetblast:
    parameters:
      freq: 5000
      gain: 6
      slope: 6
      type: Highshelf
    type: Biquad
  low shelf:
    parameters:
      freq: 1000
      gain: 6
      slope: 6
      type: Lowshelf
    type: Biquad
mixers:
  to4chan:
    channels:
      in: 2
      out: 4
    mapping:
    - dest: 0
      mute: false
      sources:
      - channel: 0
        gain: 0
        inverted: false
        mute: false
    - dest: 1
      mute: false
      sources:
      - channel: 1
        gain: 0
        inverted: false
        mute: false
    - dest: 2
      mute: false
      sources:
      - channel: 0
        gain: 0
        inverted: false
        mute: false
    - dest: 3
      mute: false
      sources:
      - channel: 1
        gain: 0
        inverted: false
        mute: false
pipeline:
- name: to4chan
  type: Mixer
- channel: 0
  names:
  - LR HP 4O
  - Tweetblast
  type: Filter
- channel: 1
  names:
  - LR HP 4O
  - Tweetblast
  type: Filter
- channel: 2
  names:
  - LR LP 4O
  - low shelf
  type: Filter
- channel: 3
  names:
  - LR LP 4O
  - low shelf
  type: Filter

asound.conf

# create a virtual four-channel device with two sound devices:
# This is in fact two interleaved stereo streams in
# different memory locations, so JACK will complain that it
# cannot get mmap-based access. see below.

pcm.multicard {
        type multi;
        slaves.a.pcm "hw:Ugreen_CM";
        slaves.a.channels 2;
        slaves.b.pcm "hw:Ugreen_RT";
        slaves.b.channels 2;
        bindings.0.slave a;
        bindings.0.channel 0;
        bindings.1.slave a;
        bindings.1.channel 1;
        bindings.2.slave b;
        bindings.2.channel 0;
        bindings.3.slave b;
        bindings.3.channel 1;
}

# JACK will be unhappy if there is no mixer to talk to, so we set
# this to card 0. This could be any device but 0 is easy. 

ctl.multicard {
        type hw;
        card 3;
}

# This creates a 4 channel interleaved pcm stream based on
# the multi device. JACK will work with this one.

pcm.multicard2 {
        type route;
        slave.pcm "multicard";
        slave.channels 4;
        ttable.0.0 1;
        ttable.1.1 1;
        ttable.2.2 1;
        ttable.3.3 1;
}
# see above.
ctl.multicard2 {
        type hw;
        card 3;
}

#
# Place your global alsa-lib configuration here...
#
#
pcm.!default { 
   type plug 
   slave.pcm "camilladsp" 
}
 
pcm.camilladsp {

    # Use the ALSA plug-in "plug" for rate-/format-conversion.
    type plug

    # Forward the audio stream to the ALSA loopback-device
    slave {
	pcm {

	    # Direct hardware access
	    type	hw

	    # Loopback card name
	    #
	    # Has to match "id" in the options of the snd-aloop module
	    card	"Loopback"

	    # Loopback device ID
	    device	0

	    # Number of audio channels
	    #
	    # Has to match the number of channels in music player app
	    # and in the CamillaDSP input configuration
	    channels	2

	    # Format of audio stream
	    #
	    # Has to match the format defined in the
	    # of the CamillaDSP input configuration
	    format	"S32_LE"

	    # Sampling-rate of audio stream
	    #
	    # Has to match the sampling-rate defined in the
	    # CamillaDSP configuration
	    rate	44100
	}
    }
}


ctl.!default {
    type hw
    card "Loopback"
}
# Create an ALSA default control-device for the ALSA loopback-device.
ctl.camilladsp {

	# Direct hardware access
        type	hw

	# Loopback card name
	#
	# Has to match "id" in the options of the snd-aloop module
        card	"Loopback"
}