MIDI NOTES.txt

Midi file chunks:

Note: B = byte. For example, if a tag specifies <4B.name> then the "name" block must be of the form 00 00 00 00.

[b] = hex representation has been broken down into binary.

<4 bytes> Type
<4 bytes> Length; number of bytes in the chunk
*Header chunks usually have 00 00 00 06 bytes

** Your programs should EXPECT alien chunks and treat them as if they weren't there.



Header chunk:
MThd<4B.length><2B.format><2B.ntrks><2B.division>

<2B.format> - format of the midi file
00 00 : the file contains a single multi-channel track
00 01 : the file has multiple simultaneous tracks
00 02 : the file has sequentially independent single-track paterns

<2B.ntrks> - number of tracks in the file
* must be equal to number of instances of MTrk in the file. if <2B.format> = "00 00" then this must be "00 01".

<2B.division> - specifies "meaning of the delta-times"
i.e. time signature

Divided into two ways (first bit)
[b] 0XXX XXXX XXXX XXXX = the Xs are # of ticks per quarter note
[b] 1XXX XXXX XXXX XXXX = subdivisions of a second, corresponding to SMPTE and MIDI time code
(this will show up as "8X XX" in hex editor most likely)

SMPTE and MIDI time code (frames per second):
if first bit is a 1, the next 7 bits contain special characters, stored in two's complement form
-24 (FF E8) = 24 frames/s
-25 (FF E7) = 
-29 (FF E3) = 30 drop frame
-30 (FF E2) = 

Example division: 10 00 FF E8...........








Track chunks

<Track Chunk> = <4B.chunk type><4B.length><?B.MTrk event>+

<?B.MTrk event> = <delta-time><event>

!! DELTA-TIMES ARE STORED AS VLQS
* represents time before the following event 

delta-time should be 0 if:
	- event is at the beginning of a track
	- two events occur simultaneously
DELTA TIMES MUST **ALWAYS** BE USED


if <division> is type 0 then delta time is a fraction of a beat
if <division> is type 1 then delta time is a fraction of a second, with SMPTE times



<event> = <MIDI event> | <sysex event> | <meta-event>

<MIDI event> -> any MIDI channel message (see appendix 1)

!! THE FIRST EVENT IN A TRACK CHUNK MUST SPECIFY STATUS (Running status)

<sysex event> -> MIDI system exclusive message
F0<length><bytes to be transmitted after F0>
length here is also a VLQ

F7 must be specified at the end of the message to indicate entire message has been read

another method:
F7<length><all bytes to be transmitted> which reduces the need for F0

<meta event> -> any non-MIDI information useful to the format or sequencers
FF<type><length><bytes> (length is 00 if there is no data)
length here is also a VLQ



MIDI messages -> channel messages or system messages

Each MIDI message has a status byte followed by one or more data bytes.

Status bytes take the form "1xxxnnnn" in binary
1 = this is a status byte
xxx = specifies the kind of midi message (0d0 - 0d7)
nnnn = channel number (0d0 - 0d15)


midi message types:

1000nnnn = note off
----nnnn = channel number; two data bytes after
<0k...> <0v...>
-- 0kkkkkkk is the key of the note to be released
-- 0vvvvvvv is the velocity that the note is released at


1001nnnn = note on
----nnnn = channel number; two data bytes after 
<0k...> <0v...>
-- 0kkkkkkk is the key of the note
-- 0vvvvvvv is the velocity of the note


1010nnnn = polyphonic aftertouch
** aftertouch messages send information about key pressure AFTER the initial velocity. [ probably not necessary ]
** polyphonic aftertouch sends the pressure information from all keys pressed polyphonically.


1011nnnn = control change
----nnnn = channel number; two data bytes after
<0c...> <0v...>
-- 0ccccccc is the controller number [see appendix]
-- 0vvvvvvv is the value the controller is set to


1100nnnn = program change
[ we can probably safely ignore this ]
<0p...>
0ppppppp is the instrument to change to


1101nnnn = channel aftertouch
** aftertouch messages send information about key pressure AFTER the initial velocity. [ probably not necessary ]
** channel aftertouch only sends the pressure information from the key with the highest pressure


1110nnnn = pitch bend change
** sends information about the pitch wheel, and allows for microtonal inflection of midi notes (has more control over note quality)
----nnnn = channel number; two data bytes after
<0l...><0m...>
0lllllll = least significant bits
0mmmmmmm = most significant bits
** these combine to one number

1111nnnn = SYSTEM MESSAGES (see above!)




Play the note C4 in channel 0 for some number of ticks:
XX 90 3C 64

Note off:

XX 80 3C 64