Doc updates from going through every file

docs/feature_audio.md

@@ -1,5 +1,91 @@
 # Audio
 
+Your keyboard can make sounds! If you've got a Planck, Preonic, or basically any AVR keyboard that allows access to the C6 or B5 port (`#define C6_AUDIO` and/or `#define B5_AUDIO`), you can hook up a simple speaker and make it beep. You can use those beeps to indicate layer transitions, modifiers, special keys, or just to play some funky 8bit tunes.
+
+If you add `AUDIO_ENABLE = yes` to your `rules.mk`, there's a couple different sounds that will automatically be enabled without any other configuration:
+
+```
+STARTUP_SONG // plays when the keyboard starts up (audio.c)
+GOODBYE_SONG // plays when you press the RESET key (quantum.c)
+AG_NORM_SONG // plays when you press AG_NORM (quantum.c)
+AG_SWAP_SONG // plays when you press AG_SWAP (quantum.c)
+MUSIC_ON_SONG // plays when music mode is activated (process_music.c)
+MUSIC_OFF_SONG // plays when music mode is deactivated (process_music.c)
+CHROMATIC_SONG // plays when the chromatic music mode is selected (process_music.c)
+GUITAR_SONG // plays when the guitar music mode is selected (process_music.c)
+VIOLIN_SONG // plays when the violin music mode is selected (process_music.c)
+MAJOR_SONG // plays when the major music mode is selected (process_music.c)
+```
+
+You can override the default songs by doing something like this in your `config.h`:
+
+```c
+#ifdef AUDIO_ENABLE
+  #define STARTUP_SONG SONG(STARTUP_SOUND)
+#endif
+```
+
+A full list of sounds can be found in [quantum/audio/song_list.h](https://github.com/qmk/qmk_firmware/blob/master/quantum/audio/song_list.h) - feel free to add your own to this list! All available notes can be seen in [quantum/audio/musical_notes.h](https://github.com/qmk/qmk_firmware/blob/master/quantum/audio/musical_notes.h).
+
+To play a custom sound at a particular time, you can define a song like this (near the top of the file):
+
+```c
+float my_song[][2] = SONG(QWERTY_SOUND);
+```
+
+And then play your song like this:
+
+```c
+PLAY_SONG(my_song);
+```
+
+Alternatively, you can play it in a loop like this:
+
+```c
+PLAY_LOOP(my_song);
+```
+
+It's advised that you wrap all audio features in `#ifdef AUDIO_ENABLE` / `#endif` to avoid causing problems when audio isn't built into the keyboard.
+
+## Music mode
+
+The music mode maps your columns to a chromatic scale, and your rows to octaves. This works best with ortholinear keyboards, but can be made to work with others. All keycodes less than `0xFF` get blocked, so you won't type while playing notes - if you have special keys/mods, those will still work. A work-around for this is to jump to a different layer with KC_NOs before (or after) enabling music mode.  
+
+Recording is experimental due to some memory issues - if you experience some weird behavior, unplugging/replugging your keyboard will fix things.
+
+Keycodes available:
+
+* `MU_ON` - Turn music mode on
+* `MU_OFF` - Turn music mode off
+* `MU_TOG` - Toggle music mode
+* `MU_MOD` - Cycle through the music modes:
+  * `CHROMATIC_MODE` - Chromatic scale, row changes the octave
+  * `GUITAR_MODE` - Chromatic scale, but the row changes the string (+5 st)
+  * `VIOLIN_MODE` - Chromatic scale, but the row changes the string (+7 st)
+  * `MAJOR_MODE` - Major scale
+
+In music mode, the following keycodes work differently, and don't pass through:
+
+* `LCTL` - start a recording
+* `LALT` - stop recording/stop playing
+* `LGUI` - play recording
+* `KC_UP` - speed-up playback
+* `KC_DOWN` - slow-down playback
+
+By default, `MUSIC_MASK` is set to `keycode < 0xFF` which means keycodes less than `0xFF` are turned into notes, and don't output anything. You can change this by defining this in your `config.h` like this:
+
+    #define MUSIC_MASK keycode != KC_NO
+
+Which will capture all keycodes - be careful, this will get you stuck in music mode until you restart your keyboard!
+
+The pitch standard (`PITCH_STANDARD_A`) is 440.0f by default - to change this, add something like this to your `config.h`:
+
+    #define PITCH_STANDARD_A 432.0f
+
+## MIDI functionalty
+
+This is still a WIP, but check out `quantum/keymap_midi.c` to see what's happening. Enable from the Makefile.
+
 <!-- FIXME: this formatting needs work
 
 ## Audio