alsa configuration file for simultaneous playback from multiple audio sources. no pulseaudio or X server needed

asound.conf

 ## alsa configuration file for simultaneous playback
 ## from multiple audio sources
 
 ## confirmed on orange pi zero, raspberry pi B+
 ## save to /etc/asound.conf
 ## http://psychip.net
 
 pcm.!default {
  type plug
  slave.pcm "dmixer"
}

pcm.dmixer  {
  type dmix
  ipc_key 1024
  slave {
    pcm "hw:0,0" #
    period_time 0
    period_size 1024
    buffer_size 4096
    rate 44100
  }
  bindings {
    0 0
    1 1
  }
}

ctl.dmixer {
  type hw
  card 0
}

ctl.!default {
    type hw
    card 0
}