Real-time MIDI router

The MIDI router is one more processing layer directly behind the MIDI input. It processes incoming MIDI events and generates control events for the synth. It can be used to filter or modify events prior to sending them to the synthesizer. When created, the MIDI router is transparent and simply passes all MIDI events. Router "rules" must be added to actually make use of its capabilities.

Some examples of MIDI router usage:

• Filter messages (Example: Pass sustain pedal CCs only to selected channels)
• Split the keyboard (Example: noteon with notenr < x: to ch 1, >x to ch 2)
• Layer sounds (Example: for each noteon received on ch 1, create a noteon on ch1, ch2, ch3,...)
• Velocity scaling (Example: for each noteon event, scale the velocity by 1.27)
• Velocity switching (Example: v <= 100: "Angel Choir"; v > 100: "Hell's Bells")
• Get rid of aftertouch

The MIDI driver API has a clean separation between the midi thread and the synthesizer. That opens the door to add a midi router module.

MIDI events coming from the MIDI player do not pass through the MIDI router.

#include <fluidsynth.h>
 
int main(int argc, char** argv) 
{
    fluid_settings_t* settings;
    fluid_synth_t* synth;
    fluid_midi_router_t* router;
    fluid_midi_router_rule_t* rule;
 
    settings = new_fluid_settings();
    synth = new_fluid_synth(settings);
 
    /* Create the MIDI router and pass events to the synthesizer */
    router = new_fluid_midi_router (settings, fluid_synth_handle_midi_event, synth);
 
    /* Clear default rules */
    fluid_midi_router_clear_rules (router);
 
    /* Add rule to map all notes < MIDI note #60 on any channel to channel 4 */
    rule = new_fluid_midi_router_rule ();
    fluid_midi_router_rule_set_chan (rule, 0, 15, 0.0, 4);      /* Map all to channel 4 */
    fluid_midi_router_rule_set_param1 (rule, 0, 59, 1.0, 0);    /* Match notes < 60 */
    fluid_midi_router_add_rule (router, rule, FLUID_MIDI_ROUTER_RULE_NOTE);
 
    /* Add rule to map all notes >= MIDI note #60 on any channel to channel 5 */
    rule = new_fluid_midi_router_rule ();
    fluid_midi_router_rule_set_chan (rule, 0, 15, 0.0, 5);      /* Map all to channel 5 */
    fluid_midi_router_rule_set_param1 (rule, 60, 127, 1.0, 0);  /* Match notes >= 60 */
    fluid_midi_router_add_rule (router, rule, FLUID_MIDI_ROUTER_RULE_NOTE);
 
    /* Add rule to reverse direction of pitch bender on channel 7 */
    rule = new_fluid_midi_router_rule ();
    fluid_midi_router_rule_set_chan (rule, 7, 7, 1.0, 0);             /* Match channel 7 only */
    fluid_midi_router_rule_set_param1 (rule, 0, 16383, -1.0, 16383);  /* Reverse pitch bender */
    fluid_midi_router_add_rule (router, rule, FLUID_MIDI_ROUTER_RULE_PITCH_BEND);
 
    /* ... Create audio driver, process events, etc ... */
 
    /* cleanup */
    delete_fluid_midi_router(router);
    delete_fluid_synth(synth);
    delete_fluid_settings(settings);
    return 0;
}