HOW THE MIDI SYSTEM
WORKS
MIDI stand for Musical Instrument Digital
Interface. It
is
an internationally
accepted standard for signal
commu-
nications between digital
music divices. More and more major manufacturers
are adopting
the
MIDI
system, and
although MIDI instruments made
by
different manufacturers are
not always totally
compatible, they should
at
least
be able to play
each other and seitch each other's voices.
The MIDI
system is what makes
it
possible
to connect ail Yamaha's digital instruments
together easily and quickly,
to
form
enormously
powerful digital music
systems.
And
it is
all
based on
a
very
simple
fact:
Any number can
be
expressed
by a
combination of
1s
and
Os.
This is also the
basis
for
the entire computer industry,
and is easily explained as follows:
We normally
express numbers using the
decimal system, which has ten different digits (including
zero)
. An
alternative
way of expressing a number is the binary system, which
used
only
two dights:
1
and
0.
The decimal
system expresses numbers as powers
of ten (one, ten,
a
hundred,
a thousand, etc.) and the
binary
system expresses
numbers as powers of two (one, two, fokur,
eight,
etc.)-
Here are
some
decimal
numbers
and
their
equivalents in the binary system.
1 1
2 10
3
11
4
100
5 101
6
110
7 111
8 1000
10 1010
16
10000
32
1
00000
64 1 000000
100
1100100
127
1111111
255 1111111
From this,
it
dit
not take
a
great quantum leap in thinking
for an unknown engineer to figure out that this meant
that any number
could be transmitted by merely switching
on and
off
an electronic pulse
signal. The
presende of
a
signal
would indicate a
1,
and the absence
of
a signal
would indicate
a
0,
and this is exactly
how
MIDI words.
Any information is broken down
into numbers,
which
usually
have a
maximum
value of 127. Why 127? Well if
you
took
at the above table of figures, you'll see that the final binary figure
is
a
row
of seven
1
s. So
1 27
is the largest
number that can be expressed using 7 digits in the binary system.
The
MIDI
standard is based
on the
use
of eight-digit
binary
numbers.
These numbers, or units of information, or
data,
are called
"bytes"
and are
said to be made up of eight
"bits"
rather than digits. The
number is sent
as 00000000,
1
as 00000001, 2 as 00000010,
3
as 0000001
1,
and
so on.
The first
bit
in
each
byte
is
used to
indicate
whether
the byte is a
"Status Byte"
(a byte
that commands
a
MIDI
Device
to
perform
a
certain operation,
e.g. "Key On")
or a "Data Byte"
(a byte that supplies the
numerical
value of data).
So
only seven bytes are used to indicate data
value, from
to 127. For
greater
numerical
data
values, more than one
byte
can
be
sent.
For
example, the
Pitch
Bend function
uses
two
bytes
giving
a
total
of
14 bits
(numerical data range 128 x 128
=
16, 384).
Each individual
bit within
a byte is
examined
by the receiving
MIDI
instrument to see if it is a 1 or a 0. Hardly a
complex procedure, which
is
why MIDI
data
is transferred incredibly quickly.
This
was
agreed upon
as the most
economical and efficient way of expressing subtle and complex information
and, simple though it seems, it does
in
fact enable
you to create music that is MORE subtle than
you
can perceive!
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