What is a MIDI message, really ?

• A MIDI message is a sequence of ‘byte values’.
• A byte is a series of 8 ‘bits’, which have a value of 0 or 1. So for example, a byte might be ‘01101001’.
• When using DINs, bits are transmitted by wiggling the voltage on the wire. The MIDI standard uses +5V to represent ‘1’, and 0V to represent ‘0’. Each byte also has a ‘start bit’ and a ‘stop bit’. So really, in MIDI, there are 10 bits per byte.
• A byte has 256 different possible combinations of bit values, so it has a ‘value’ of 0 to 255.
• So as an example, the message ‘note on, middle C, channel 2, velocity 80’ is actually 3 bytes, and looks like this, as a series of bits :

0

0

1

1

1

1

0

0

0

1

0

0

0

0

0

0

1

0

0

1

0

0

0

1

start bit

stop bit

control/data bit

control/data bit

control/data bit

2

3

4

5

6

7

8

9

1

10

12

13

14

15

16

17

18

19

11

20

22

23

24

25

26

27

28

29

21

30

msg type

channel

note number

velocity

control byte

data byte 1

data byte 2