pcm.mixer {
  type dmix
  ipc_key 1024
  ipc_key_add_uid false  # remove these two lines to only allow
  ipc_perm 0666          #  one user to use the mixer at a time.
  
  slave {
    pcm "hw:1,1"         # hardware output device to use.
  }
}

pcm.!default plug:mixer  # set the default device to the mixer.