From: META000 <META@UNB.CA>
Subject: Re: What is MIDI?
Organization: The University of New Brunswick
Date: Sat, 9 Jan 1993 17:54:42 GMT

As a developmental psychologist, I'm trained to believe that we
understand things better when we know how they came about.  In that
spirit, a brief bit of history regarding MIDI.

Early keyboard synthesisers were constructed with two switches under
each key. When you pressed the key down and closed the switches, two
things happened: a "gate" signal was generated that indicated a note
was now being played, and a connection was made along a lengthy
series of resistors which emulated a voltage divider (for the
lo-tech, it's like avolume control works).  The voltage created
served to control a voltage-controlled oscillator which would
produce a tone proportional in pitch to the voltage.  Since the
oscillator was essentially always "on", the presence and absence of
a "gate" signal (also generated by a key press) would allow the
voltage-controlled-amplifier to either amplify or not amplify the
oscillator signal being fed to it (I am leaving out a number of
stages of processing here for the purposes of simplification).
Since the wire going from the keyboard to the oscillator was
carrying an analog signal, wire quality and length were critical
concerns since any change in voltage produced by leakage or some
other factor would make the oscillator behave differently, and
likely beout of tune.  Moreover, since the pitch of the oscillator
depended on things like supply voltage, input voltage, and
temperature, stability was always an issue; things were simply
difficult to keep in tune.  Music-tech magazines of the mid-70's to
early 80's seemed to always have improved-stability oscillator
circuit designs, and any of the major synthesists interviewed always
seemed to have something to say about oscillator stability, and
wierd tips for achieving it (like warming things up, etc.).

The other problem with early analog synths was that the conventional
way of used a keyboard-based voltage divider limited one to only
being able to play a single note (although there were some fancy
ones that could play two notes) at a time.

Enter digital coding...

If the note being played could be represented by a code, instead of
a directly proportional voltage, then even if the digital code that
started out at 5volts turned into 4.7 volts by the time it hit the
synth, it would still be the code for the desired note. Also, heat
and instability would not be nearly as much of a problem.

The big bonus, however, is that if information about what the
fingers are doing could be turned into a digital code, then all you
had to do to play polyphonically was to simply read the keyboard for
which keys were being pressed, and send the data to something which
could remember those data.

Consequently, early MIDI implementations were directed primarily at
being able to overcome the problems of oscillator drift/tuning and
being able to play more than two notes at a time.  The nice thing
about converting from the analog to the digital domain was that once
all your info was in coded (digital) form, it could be stored.  Not
only that, but if all that was being sent was a digital code, then
as long as you had some way of converting analog or
instructioninformation into a digital code,and as long as you some
way/device to interpret it, you didn't have to be restricted to just
information about notes being played.

Which brings us to the present.  MIDI is a hardware/software
standard for sending and receiving information in a way that is
compatible with the **purposes** of music.  Consequently, one
needn't be restricted to noteinformation.  One can send information
about particular settings for particular devices so as to control
remote devices.  MIDI has been employed to run lighting systems,
mixers, delay lines, etc.  As long as the receiving device is equipped
with MIDI, and has built-in firmware for decoding the relevant
messages and using them, and as long as the sending device is
capable of generating that data (not all devices can send all
conceivable codes)then you can use MIDI to control just about
anything.

As mentioned above, it is a standard for sending info for the
purposes of music.  As of 1982, the first MIDI standard transmitted
information at a rate that permitted one to play pretty much as fast
as you could and have the information decoded by a remote device and
turned into sounds without much appreciable delay, often about 3msec
I'm told.  Of course, by 1993,the "purposes" of music had changed
considerably.  We now assume that weshould be able to, on a note by
note basis, specify not only what note we are playing, and how hard
we struck the key and whether the note is on or off, but also what
effects we are using, their settings, whether we've bent the note or
not, and innumerable other things.  For this reason, many players
have found the original MIDI standard, with its' 31.4kbd rate of
transmission too limiting and simply not fast enough.

Newer MIDI standards are being worked on so as to accommodate
sending more information perunit of time, in a more flexible or
malleable way.  Remember, all of this MIDI crap is designed, at
least in part, to allow the synthesist to have real-time control
over as many performance parameters as the acoustic
guitarist/pianist/reed player has in their fingers, toes, and
breath.  We normally have an incredible array of performance parameters
that we can change simply by tilting the pick, where we pluck, how
close to the amp we are, and on and on.  MIDI is aiming towards
being able to provide that kind of instantaneous flexibility forthe
electronicmusician, that sheer physics and practice provides for the
acoustic musician.

Hope this is edifying.  Mark Hammer