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WHAT'S MIDI?
Musical Instrument Digital Interface (MIDI) is a way for keyboards,
synthesizers, sequencers, rhythm machines, and computers to commu-
nicate with each other. Devices that have a MIDI jack can be connected
together to send and receive information. Since most musical instru-
ment manufacturers have agreed on MIDI, you can connect devices of
various manufacturers.
Each piece of information is called
a MIDI
MESSAGE.
Each MIDI
message is made up of 1 to 3 bytes (numbers); a Status Byte and 0,1
or 2 Data Bytes.
The typical MIDI message is in the following form:
Sn. xx. yy
S=
Status (8-E)
=
Channel number (0-F indicates channel 1-16)
xx=
First data byte (00-7F)
yy=
Second data byte (00-7F)
Let's look at a sample 3-byte MIDI message.
93. 3C. 15
Status (Note On)
Channel #4
Note #
Velocity
For example, if a DX7 synthesizer receives this message, it does the
following.
1.
Checks the channel number to see if it is acceptable. If the DX7 has
been set to receive that channel, it goes on to the next step. If not,
the message is ignored. In the example above, the channel number
is 4. (We count 0-F as 1 to 16.)
2.
Checks the status. In this case, the status is Note On, so the DX7
knows to expect two more data bytes; note number (what note)
and velocity (how hard it was hit).
3.
Reads the data bytes and produces the correct note with the correct
velocity.
(Keep in mind that all this takes a very short time. It takes about 1
/ 1000 of a second to send a MIDI message. To
us, it seems as
though sound is produced at the same time the key is pressed.)
yy Eo
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