Notes on the soundfront2 and midi formats

frere_jaques.c

#include <fluidsynth.h>
#include <unistd.h>

// global vars have external linkage by default (https://stackoverflow.com/a/4239955/2228912)
static fluid_settings_t *settings;
static fluid_synth_t* synth;
static fluid_audio_driver_t* driver;

// global constants also have external linkages (https://stackoverflow.com/a/13185812/2228912)
// Key for C4 (middle C) = 60 (key code incremented by one when going a half-tone up)
// int c4 = 60;
static const int G4 = 67;
static const int A4 = 69;
static const int B4 = 71;
static const int C5 = 72;
static const int D5 = 74;

// midi channel to play notes on (max for midi = 16)
static const int CHANNEL = 0;

// sleep determines duration (leaves time for note to play)
static const unsigned int DURATION = 500 * 1000; // 500ms

// how hard key was struck (max = 127)
static const int VELOCITY = 127;

/* free() do nothing when called on NULL pointers */
static void clean_up() {
  // driver must be the first to delete (depends on others) => reverse order of init.
  delete_fluid_audio_driver(driver);
  delete_fluid_synth(synth);
  delete_fluid_settings(settings);
}

static void play_note(int note) {
  fluid_synth_noteon(synth, CHANNEL, note, VELOCITY);
  usleep(DURATION);
  fluid_synth_noteoff(synth, CHANNEL, note);
}

/**
 * Plays first few notes from "Frere Jaques" using Fluidsynth C API
 * Frere Jaques (Key of G): https://www.true-piano-lessons.com/frere-jacques.html
 * Reference: https://www.fluidsynth.org/api/UsageGuide.html
 *
 * Build & run:
 * $ gcc -lfluidsynth freres_jaques.c -o app
 * $ ./app /usr/share/soundfonts/FluidR3_GM.sf2
 */
int main(int argc, char* argv[]) {
  if (argc != 2) {
    printf("USAGE: %s SF2-FILE\n", argv[0]);
    return 1;
  }

  // settings
  settings = new_fluid_settings();
  if (settings == NULL) {
    printf("Failed to create settings\n");
    clean_up();
    return 1;
  }

  // synthesizer
  synth = new_fluid_synth(settings);
  if (synth == NULL) {
    printf("Failed to create synthesizer\n");
    clean_up();
    return 1;
  }

  // soundfont
  const char* path_sf2 = argv[1];
  int id_soundfont = fluid_synth_sfload(synth, path_sf2, 1);
  if (id_soundfont == FLUID_FAILED) {
    printf("Failed to load soundfont\n");
    clean_up();
    return 1;
  }

  // audio driver: alsa, pulseaudio, jack... (must be last one to create)
  // starts playing audio (in separate thread) once driver created
  driver = new_fluid_audio_driver(settings, synth);
  if (driver == NULL) {
    printf("Failed to create audio driver\n");
    clean_up();
    return 1;
  }

  // play first notes from "Frere Jaques"
  for (size_t i = 0; i < 2; i++) {
    play_note(G4);
    play_note(A4);
    play_note(B4);
    play_note(G4);
  }

  for (size_t i = 0; i < 2; i++) {
    play_note(B4);
    play_note(C5);
    play_note(D5);
    usleep(DURATION);
  }

  clean_up();

  return 0;
}

Soundfront2-notes.md

SF2 format

• File format (binary) storing multiple instruments.
• Stores instrument samples to play MIDI.
• Samples are stored:
  • For each note of an instrument (e.g. all piano keys).
  • Possibly multiple velocities by key (how hard the note was struck).
• Polyphone can be used to read sf2 files.
• soundfont-fluid and freepats-general-midi provide free samples in sf2 format (installed to /usr/share/soundfonts/).
• Jack2: is an audio server like pulseaudio and alsa but professional audio production thanks to its low latency:

$ sudo pacman -Sy jack2 jack2-dbus
$ jack_control start

Synthesizers

• timidity:

$ sudo vim /etc/timidity/timidity.cfg
...
soundfont /usr/share/soundfonts/FluidR3_GM.sf2 # <= line to add
...
$ timidity <file.mid>

• fluidsynth:

$ fluidsynth <file.sf2> <file.mid>

Midi file

• Binary file.
• It doesn't contain samples or instrument sounds.
• It contains instead notes played, with their pitches, velocities...