From: rfries@sceng.ub.com (Robert Fries)
Subject: Re: What is MIDI?
Organization: Ungermann Bass
Date: Thu, 7 Jan 1993 21:23:23 GMT

In article <8fH6cnO00iUx02JlgP@andrew.cmu.edu> Bill Thomas <bt16+@andrew.cmu.edu> writes:

>>The subject says it all. Forgive my ignorance but could some kind soul
>>explain what MIDI stands for? I have seen it in many posts and
>>descriptions of guitar synth's, but have no idea what it is. As you
>>can see, I am new to the subject.  Many thanks.

>I probably shouldn't try answering this, but what the heck:

>The term MIDI stands for Musical Instrument Digital Interface, meaning,
>of course, that it's a digital interface for a musical instrument --
>usually electronic keyboards, but guitars also. It involves a set of
>computer hardware and software that allows you to apply the digital
>processing power of a computer to an instrument. You pull the sound from
>the instrument into the computer, change it digitally, and feed it back
>through the amplification system. With keyboards, MIDI systems use the
>digital information that makes up the "sound" as a sort of raw material
>that can be shaped, theoretically, into virtually any sound (though
>that's probably overstating it a bit). I assume the same is true for an
>electric guitar with a MIDI hookup, though I've never used one.

Right, you shouldn't try answering this, Bill :-) :-)

MIDI basically defines a hardware and software protocol for controlling
musical devices. 

The hardware spec defines electrical characteristics
of the devices attached. 

The software protocol describes a standard set of commands, which 
make sense to musical instruments. The software protocol defines messages
which may be sent, and defines a method of addressing multiple devices
on the MIDI 'network'. These addresses are called channels, and most 
MIDI devices allow you to configure them to send/receive messages on 
different channels. Thus, several attached devices may be controlled
independently.

These message are mostly of the type:	
	channel X, turn note Y ON
	channel X, turn note Y OFF

This is greatly simplified, the note on and note off commands
can also send velocity info, which synths can used to determine
how loud a note should be played. Note OFF velocity is little used,
as far as I can tell.

Additional messages are defined for program change, which tells 
a device to change the voice played on a given channel.

In addition, MIDI provides a facility for manufacturers to 
implement their own, system exclusive messages. These would
be used to support features not found in all devices, and would not
usually be portable to other types of devices.

These 'system exclusive commands' can be defined (by the synthesizer maker)
to perform operations like 'dump all voices', set voice parameters,
and others. At this level, MIDI might be used to load sound info, modify it,
and send it back to a synth.

However, the predominant use is to allow a sequencer, or a computer running
sequencer software, to 'play' one or more instruments attached to a
MIDI 'network'. These are typically synthesizers and drum machines,
though some tape decks, guitar preamps, effects devices can be controlled
via MIDI.

This is by no means a complete explanation of MIDI; however,
it is basically correct.

I hope this clarifies things a bit.

Robert

//////////////////////////////////////////////////////////////////////////
Robert Fries
Ungermann-Bass Inc.

DISCLAIMER:
    Opinions contained herein are my own, and are not necessarily those
    of Ungermann-Bass.
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