Document size added by MIDI_ENABLE (~3800 bytes according to my experiments)

satan/keymaps/midi

MIDI_ENABLE = no

   text	   data	    bss	    dec	    hex	filename
      0	  17080	      0	  17080	   42b8	satan_midi.hex

MIDI_ENABLE = yes
#define MIDI_TONE_KEYCODE_OCTAVES 3 // default

   text	   data	    bss	    dec	    hex	filename
      0	  20846	      0	  20846	   516e	satan_midi.hex

MIDI_ENABLE = yes
#define MIDI_TONE_KEYCODE_OCTAVES 2 // fewer octaves

   text	   data	    bss	    dec	    hex	filename
      0	  20846	      0	  20846	   516e	satan_midi.hex

keyboards/satan/keymaps/midi/Makefile

@@ -9,7 +9,7 @@ CONSOLE_ENABLE = no         # Console for debug(+400)
 COMMAND_ENABLE = yes        # Commands for debug and configuration
 NKRO_ENABLE = yes           # Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
 BACKLIGHT_ENABLE = yes       # Enable keyboard backlight functionality
-MIDI_ENABLE = yes            # MIDI controls
+MIDI_ENABLE = yes            # MIDI support (+3800)
 AUDIO_ENABLE = no           # Audio output on port C6
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID

keyboards/satan/keymaps/midi/config.h

@@ -5,7 +5,7 @@
 
 // place overrides here
 
-/* override number of MIDI tone keycodes (each octave adds 12 bytes) */
+/* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 #define MIDI_TONE_KEYCODE_OCTAVES 2
 
 #endif

keyboards/satan/keymaps/midi/keymap.c

@@ -32,6 +32,7 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
   KC_LSFT,         KC_Z,   KC_X,   KC_C,   KC_V,   KC_B,   KC_N,   KC_M,   KC_COMM,KC_DOT, KC_SLSH,         KC_RSFT, \
   KC_LCTL, KC_LGUI,KC_LALT,                KC_SPC,                                 KC_RALT,KC_RGUI, TG(_ML), KC_RCTL),
 
+#ifdef MIDI_ENABLE
 /* Keymap _ML: MIDI Layer
    * ,------------------------------------------------------------------------.
    * | Exit |    |    |    |    |    |    |    |    |    |    |    |    |     |
@@ -57,4 +58,5 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
   MI_MOD,  MI_C,    MI_D,    MI_E,    MI_F,    MI_G,    MI_A,    MI_B,    MI_C_1,  MI_D_1,  MI_E_1,  MI_F_1,           _______, \
   MI_SUS,  MI_OCTD, MI_OCTU, MI_MODSD, MI_MODSU, XXXXXXX, XXXXXXX, XXXXXXX, MI_TRNSD, MI_TRNSU, MI_TRNS_0,             MI_SUS, \
   _______, _______, _______,                          MI_OFF,                               _______, _______, _______, _______),
+#endif
 };

quantum/process_keycode/process_midi.c

@@ -1,3 +1,5 @@
+#define MIDI_TONE_KEYCODE_OCTAVES 2
+
 #include "process_midi.h"
 #include "timer.h"
 

quantum/template/config.h

@@ -159,7 +159,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //#define NO_ACTION_MACRO
 //#define NO_ACTION_FUNCTION
 
-/* override number of MIDI tone keycodes (each octave adds 12 bytes) */
+/* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 //#define MIDI_TONE_KEYCODE_OCTAVES 1
 
 #endif

quantum/template/keymaps/default/Makefile

@@ -9,7 +9,7 @@ CONSOLE_ENABLE = no         # Console for debug(+400)
 COMMAND_ENABLE = yes        # Commands for debug and configuration
 NKRO_ENABLE = yes           # Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
 BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
-MIDI_ENABLE = no            # MIDI controls
+MIDI_ENABLE = no            # MIDI support (+3800)
 AUDIO_ENABLE = no           # Audio output on port C6
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID