MIDI messages are made up of status and data bytes. The status byte indicates the type of message and data bytes provide additional details. Common MIDI messages include Note On/Off to play notes, Controllers to control parameters, and Program Changes to switch presets. MIDI allows connection of multiple devices in daisy chains with different channel and mode settings to route messages.

1. MIDI Messages: general concepts
(…….this is important!)
The MIDI protocol is made up of a series of messages of 8-bit
bytes.
The first byte of the message is the status byte, residing in the
range 128-255.
The remaining bytes of the message (called data bytes) will be in
the range 0-127.
The first bit of a status byte is always a 1; the first bit of a data
byte is always a 0.
There is 1 start bit, 8 data bits, and 1 stop bit, for a period of
320 microseconds per serial byte or 3,125 bytes per second.
MIDI transmits a variety of messages used to express different
musical attributes and performance functions.

2. Note On
Q. Who’s on first?
A. Status byte = kind of event or function…..Data byte(s) follow(s) with the details.
DATA BYTE INDICATING
KEY VELOCITY = 64
MIDI OUT
01000000
DATA BYTE INDICATING
KEY #60 = MIDDLE C
00111100
10010000
MIDI IN
STATUS BYTE FOR
NOTE ON MESSAGE

3. Note off
DATA BYTE INDICATING
KEY VELOCITY = 0
DATA BYTE INDICATING
KEY VELOCITY = 64
00000000
MIDI OUT
00111100
01000000
DATA BYTE KEY #60
= MIDDLE C
STATUS BYTE FOR
NOTE ON MESSAGE
10010000
MIDI IN
00111100

4. Transmitting a C+ chord in root position
Note On/Note Off/Velocity
00000000
DATA BYTE G KEY
VELOCITY = 63
01000011
00000000
MIDI OUT
01000000
00000000
00111100
00111111
DATA BYTE KEY #64
= G above mid. C
DATA BYTE E KEY
VELOCITY = 68
01000011
01000100
01000000
01000000
MIDI IN
10010000
00111100
DATA BYTE KEY #64
DATA BYTE
= E above mid. C
KEY VELOCITY = 64
DATA BYTE KEY #60
STATUS BYTE FOR
= MIDDLE C
NOTE ON MESSAGE

5. Controllers
MIDI allows for up to 121 devices that transmit
Control Change Messages between values of 0 – 127.
Standard MIDI Controller #s. 0 - 63 designate
continuous message devices i.e. 1 = mod. wheel, 4 =
foot pedal, 7 = volume pedal.
Controllers 64 - 120 designate switch devices with
values 64 - 127 = On.
Pitch change messages provide 16,384 steps of
resolution to accommodate the ear’s acute sensitivity
to pitch.
Excessive use of controllers in a dense musical
arrangement can lead to an overload of MIDI’s
transmission capacity.

6. Example of Continuous Data Controller
00000000
01000011
00010001
00000111
MIDI OUT
00001010
00000111
00000110
DATA BYTE KEY #64
= G above mid. C
DATA BYTE BREATH
CTLR. = 2
01000011
00000010
10110000
10010000
00111100
MIDI IN
STATUS BYTE FOR
NOTE ON MESSAGE
01000000
STATUS BYTE FOR
CTL. CHANGE MESSAGE

7. Pitch Bend
MIDI OUT
ETC……...
MOST SIGNIFICANT
DATA BYTE
LEAST SIGNIFICANT
DATA BYTE
00000110
00000000
11100000
10010000
00111100
MIDI IN
STATUS BYTE FOR
NOTE ON MESSAGE
01000000
STATUS BYTE FOR
PITCH CHANGE MESSAGE

8. Program Changes
MIDI OUT
DATA BYTE INDICATING
PRESET PROGRAM
NUMBER
STATUS BYTE FOR
PGM. CHANGE
MESSAGE
MIDI IN
00111100
11000000

9. Channels and Modes
MIDI allows for up to 16 channels/cable port utilizing 4
possible modes to create elaborate multi instrumental
arrangements.
2nd nibble of a status byte is used to represent numbers 1 – 16.
Four possible combinations of Omni On/Off and Poly/Mono
are used to configure synths to respond or ignore channel
messages, or to operate in a poly- or monophonic mode.
Omni-On/Poly, Omni-On/Mono, Omni-Off/Poly, OmniOff/Mono.
Synthesizers have a limited number of available voices.

10. Practical Assignments:
Set up the following examples of Daisy Chains.
Test MIDI program change messages and channel assignments.
Test MIDI data flow from one device to the next.
IN
IN THRU OUT
THRU
OUT
Keyboard*
Computer/
Sequencer
* Omni-On (Off)/Poly Mode

11. Example of Daisy Chain
IN
THRU
OUT
Keyboard
IN
THRU
OUT
Keyboard
IN
THRU
Module
OUT

12. Example of Daisy Chain
IN
THRU
OUT
Keyboard
IN
THRU
OUT
Keyboard
IN
THRU
Module
OUT

13. Example of Daisy Chain
IN
IN THRU OUT
THRU
OUT
Keyboard*
Computer
IN
THRU
OUT
Keyboard
IN
THRU
Module
*CTL.TYPE SET TO BOTH/THRU???
OUT