How The Midi System Works - Yamaha TX 816 Owner's Manual

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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