midi for newbs - note

So your midi controller sends notes and controls on channels to a sound module. What exactly is a note then...?

Each time you press or release a key on your controller, a little "event" is sent across the midi wire containing the note info. Let's say you played a c major chord and held it for a second. The activity on the midi cable would look something like this: 
 Time     Chan  Note  Up/Dn  Velocity
 0001.1.0    1  4c    Down   100
 0001.1.0    1  4e    Down    98
 0001.1.0    1  4g    Down    98
 0001.1.100  1  4c    Up      64
 0001.1.100  1  4g    Up      64
 0001.1.103  1  4e    Up      64
time
time is a number of "ticks" in music time. It's usually displayed as bars.beats.ticks
channel
1 means you used channel 1 and the sound for the chord will be whatever sound is assigned to channel 1. Probably piano.
note
4c means octave 4 note C (middle C)
down/up
Down means the key was pressed. You get a seperate Up event when the key is released later.
velocity
how fast (or hard) the key was pressed/released. 1 for VERY softly - probably no sound. 127 for banged on as HARD as possible - loud! Some keyboards also give a velocity on the key up event. Some just always set it to 0 or 64.


Note that in this example, you pressed the C note a little harder than the other 2 in the chord. Also note that you let up on the G a little earlier than the E. Possibly by a few microseconds. Midi timing is very precise.


When these note down (note on) and note up (note off) events are stuffed into a file, the exact time that each event happened is stuffed in too. This let's a midi sequencer (a music program) repeat your exact performance.


Really exact? Well, some would argue that this isn't an exact replication since your keypresses are turned into 1..127 Not the possibly more subtle velocities a human is capable of. But, well, I'll let you decide about that. To me, 1..127 seems pretty dang dead on.


Octaves


Synth manufacturers don't agree on how to number octaves. The standard is that octave 4 is middle C. Note that octaves start at 0. A0 is the usual lowest note on an 88 key keyboard. But there's no G0. Just be careful reading octaves in the docs for your synth.


How midi compares to sheet music


Midi is an exact performance of a song. Sheet music doesn't get this detailed. It doesn't specify how hard to press and release each note. All times are divisions of the beat - no ticks.

There are timing and dynamics markings in sheet music. But these are pretty general and left up to you for an actual interpretation.

Going from sheet music to midi is pretty straight forward. But if you play that out a midi sequencer, it'll be pretty boring. Every note at velocity 100. No rubato ever. Not how a human would play it.

Going from midi to sheet music is even worse. A note time or duration in midi will likely not convert to standard notation well at all. Sheet music notes have "perfect durations". Playing legato or stacatto may not map to standard notation durations. At all.

Often, you'll have one midi file of "just the sheet music" to learn. And another midi file of your performance with "expressive" notes.




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