E-Mu EMAX II, Руководство по эксплуатации, Страница: 234 / 257

Emax II operation manual
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BASICS: QUESTIONS AND ANSWERS ABOUT MIDI
MIDI is causing a certain amount of confusion among musicians. Fear not-it’s not all that
hard to understand, and the Emax II makes it particularly easy to deal with. For those
of you who aren’t that familiar with MIDI, we’ll first answer some common questions.
What does the MIDI cable do?
An instrument already has an AC cord that carries electrical current, and an audio cord
that carries audio signals to an amplifier. Now you have a third connection: the MIDI
cable. This carries neither audio nor power, but transmits information about the status
of the instrument to, and receives “status reports” from, other MIDI instruments. This
information is coded in a computer language...a somewhat primitive language with few
words and several dialects, but a language nonetheless.
What does MIDI stand for?
MIDI stands for Musical Instrument Digital Interface. You already know what “musical
instrument” means, so that takes care of the first half of this phrase.
Digital means that
the instrument’s information is conveyed in digital, or computer, language. Interface is
the term for the actual link between instruments, where data passes from one instrument
to another. So MIDI is a link between musical instruments that speaks data in computer
language.
How can information control a synthesizer?
First we need to know a bit about computers, since MIDI instruments have microcom-
puter souls...in fact, MIDI could not exist without microcomputers.
Computers are decision makers, and they base those decisions on the data they receive.
However, to be useable by a computer any data has to first be translated into a number-
based language that the computer can understand. Actually, when you press a keyboard
key with a computer-based instrument, you are not directly controlling the sound
source. Instead, each time you close a keyboard switch you’re sending a number to the
computer, and this
number tells the computer what note you want it to play for you.
The computer’s “window on the world”, where it receives and transmits numerical data,
is called its
data bus . The computer looks to see whether any information is on the data
bus, and if so, acts on this data. For example, if it sees a digital “word” that says “play
F#” on the data bus, it will do as the data commands and control a sound source so that
it plays an F#. However, note that the computer doesn’t care whether this word is placed
on the data bus due to closing a keyboard switch or striking a guitar string—once MIDI
translates a note into computer language, the note becomes compatible with any device
that speaks the same language. MIDI provides access to the computer’s data bus and
selects which device will be “on the bus” at any particular moment, thus letting you
determine the flow of information from one MIDI device to another. This is why having
a specification that manufacturers can follow is so important; it insures that a variety of
otherwise incompatible devices will be able to communicate with each other over a
common data bus.
MIDI SUPPLEMENT
MIDI Q & A