How can I direct the output both of mpg123, and of eSpeak to the same ALSA sound device?

Question

I'm currently struggling with the following scenario: I'd like to make my Raspi (3B) play a short MP3 jingle and then, after a 250 µsec pause, speak a short text by using an add-on sound card (JustBoom DAC HAT). Both mpg123, and eSpeak are running separately, buth all attempts to run them one after another from a C++ client app, were futile 'cause eSpeak complained about sound card #1 not working. My HAT, however, is card #0 in the alsa config file, and on-board sound has been kicked out of the config:

pcm.!default {
  type plug

  slave {
    pcm "hw:0,0"
    format S32_LE
    channels 2
    rate 192000
  }
}

ctl.!default {
        type hw
        card 0
}

hw:0,0 is my JustBoom card:

pi@autoradio:/import/valen/autoradio $ aplay -l
**** Liste der Hardware-Geräte (PLAYBACK) ****
Karte 0: sndrpijustboomd [snd_rpi_justboom_dac], Gerät 0: JustBoom DAC HiFi pcm512x-hifi-0 []
  Sub-Geräte: 1/1
  Sub-Gerät #0: subdevice #0

Here is the error message:

ALSA lib confmisc.c:768:(parse_card) cannot find card '1'

An obvious alternative would be PulseAudio, but I've never managed to make it play anything, as client code keeps on complaining about a refused connection.

So is there a method to make bith mpg123, and eSpeak coexist peacefully and play their sounds one after the other without conflicts? Thank you.

Answer 1

OK, I've found out that mpg123 and eSpeak stumble upon each other whilst trying to spit out their sound data through the sound card. Configuring an output mixer in /etc/asound.conf resolved the issue. Here is the complete config file, taken from the ALSA project website and adapted to my needs:

pcm.dmixer {
    type dmix
    ipc_key 1024
    ipc_perm 0666
    slave {
        pcm "hw:0,0"
        period_time 0
        period_size 1024
        buffer_size 4096
        rate 192000
        format S32_LE
        channels 2 
    }
    bindings {
        0 0
        1 1
    }
}

pcm.dsnooper {
    type dsnoop
    ipc_key 2048
    ipc_perm 0666 
    slave 
    {
        pcm "hw:0,0"
        period_time 0
        period_size 1024
        buffer_size 4096
        rate 192000
        format S32_LE
        channels 2 
    }
    bindings {
        0 0
        1 1
    }
}

pcm.duplex {
    type asym
    playback.pcm "dmixer"
    capture.pcm "dsnooper"
}

pcm.!default {
    type plug
    slave.pcm "duplex"
}

ctl.!default {
    type hw
    card 0
}