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 Post subject: The language of Midi
PostPosted: Tue Mar 13, 2007 3:26 am 
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Mr. Electonica Dude
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Like any language midi uses words as well. A word in midi is called a message ! Now we will get familiar with the most important messages in the midi language.

The most common midi message is the note on and note off messages. So to recap , a note on message means switch note on and the note off is a no brainer. How in the heck does the sound generator know which key was pressed ? Which note was switched on ? Have you ever watched a keyboard players hands and wondered how the sound generator knows how hard the key was pressed and how loud ?
The note on message has all the answers. When a key is pressed there is actually more going on than note on and off. (That's why some midi files sound so cheesy and artificial. ) Note on/off and nothing in between.

A modern keyboard generates several types of information. (1) A key was pressed. (2) Which key was pressed. (3) How hard the key was pressed.

The first statement is called the data byte. The data is the same for every key and simply says "Hey ! Somebody pressed a key more info will follow !"

The second statement is called the first data byte and varies with what key is pressed. Midi numbers all notes from C2 to G8 from low to high. The number of the note is called the midi note number. You can count 'em if you want but rest assured there is plenty of note numbers to represent a concert grand (88 keys) with lotsa leftovers. Now you all know that starting at any note , each note ascending up the keyboard (or fretboard) is one half step above the preceding one. On the keyboard , the pattern repeats every 12 notes. (it's a little more complicated for you guitar players but you get the idea. Right ? ) Middle C is midi note #60. High C on the piano is midi note #108. Getting the picture ?

The third statement is called the second data byte . How hard did we press the key? The term "how hard " may be the wrong term to use as what is actually measured is "how fast" or velocity ! What is actually measured is how long it takes from the initial motion of the key until it touches the bottom of it's travel. The midi numbers 1 thru 128 represent the slowest one can operate the key to the fastest we can play it. (without breaking things).

That brings us to the note off message again. What happens when the key is released ? Note off data ends the midi message and brings us silence.

For simplicity's sake I left out the aftertouch data byte explanation as it does not apply equally to guitar players as it does to keyboards. But if your curious , aftertouch is usually a 1 or a 128 (off or on) with nothing in between. Some cool things can be done with aftertouch such as pressing harder on the keyboard after the initial velocity and not letting the key return. On my Hammond , I sometimes assign aftertouch to speed up or slow down the Leslie horns freeing my feet to play the bass pedals instead of using the Leslie footswitch. A step firther , I could also assign another controller to take the place of aftertouch i.e. I could assign a breath controller to run the Leslie. Just as easily , I could assign a Koass pad stroke direction , a mod wheel , or a sequencer to do the same thing.

Are things starting to make sense ?

Next time...More Silly Messages

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