Wednesday 30 May 2012

Found low latency for Karaoke with PulseAudio

As a followup to the last post: I can now play Midi files and sing along with no noticeable latency using PulseAudio. To direct the (default) microphone to the (default) speaker load the module_loopback (thanks to rusty0101):

    pactl load-module module-loopback latency_msec=1

Everything you speak/sing/holler will then be played on the speaker.

For Midi file playback I discovered FluidSynth. The following program will play a Midi file:

// See

// Run by ./PlayFile /usr/share/soundfonts/FluidR3_GM.sf2 ../54150.mid

int main(int argc, char** argv)
    int i;
    fluid_settings_t* settings;
    fluid_synth_t* synth;
    fluid_player_t* player;
    fluid_audio_driver_t* adriver;
    settings = new_fluid_settings();
    synth = new_fluid_synth(settings);
    player = new_fluid_player(synth);

    fluid_settings_setstr(settings, "audio.driver", "pulseaudio");
    // Use paman to find output device's name
    fluid_settings_setstr(settings, "audio.pulseaudio.device",

    adriver = new_fluid_audio_driver(settings, synth);
    /* process command line arguments */
    for (i = 1; i < argc; i++) {
        if (fluid_is_soundfont(argv[i])) {
           fluid_synth_sfload(synth, argv[1], 1);
        if (fluid_is_midifile(argv[i])) {
            fluid_player_add(player, argv[i]);
    /* play the midi files, if any */
    /* wait for playback termination */
    /* cleanup */
    return 0;

And whadda-you-know? It all works fine.

There's just the matter of hooking up a GUI, and a few thousand lines of code. But at least I'm starting from a good base, and I now realise the Java Sound framework can't give me that, sad to say.

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