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Home | Technical | MIDI | System Exclusive Messages

System Exclusive Messages

Hexadecimal Format

System exclusive messages can be very confusing, especially to the beginner. The fact that they are written in hexadecimal means that they immediately look a little alien and do not have the same meaning to us as the more familiar decimal format. Unless you have spend a great deal of time working with computers and hexadecimal numbers you will find that you have to translate them into decimal to comprehend them.

Hexadecimal is base sixteen and as we only have ten numeric symbols (0-9) it is necessary to use a letter of the alphabet to represent the numbers 10-15. Zero to fifteen in hexadecimal is written:

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
(Leading zeros are obligatory in sysex commands).

Once you reach sixteen the system clocks over as it does at ten in decimal so that the fifteen you have already counted becomes one unit of fifteen. 10 is sixteen in hexadecimal which is where you must be careful that you know what format the data you are looking at is in. 0x or 0X is usually used to indicate that the number following is in hexadecimal format but sometimes you will see h or hex.

Synthesiser Exclusive

The other confusing aspect of system exclusive messages is the exclusive part. Because they are designed to convey data to specific hardware the actual content of the messages is not fixed. This often means that you will have to spend time looking at confusing tables in often badly written synthesizer manuals to find the information that you need. Having said this, there are some rules that do apply to system exclusive messages that will help you make sense of it all.

Common Rules

System exclusive messages are written in HEXADECIMAL.
System Exclusive commands always start with F0. This tells the synthesiser to expect a message.
System Exclusive commands always end with F7. This tells the synthesiser that the message is over.
The values must be formatted with two digits so leading zeros are sometimes required.
Zero is always the first number as far as computers are concerned so effect 1 may actually require a value of zero.

Breakdown of a Simple Message

F0 - Alerts the synthesiser to the fact that a sysex message is imminent.
43 - Identifies the manufacturer of the synth that this message is for. (In this case Yamaha)
10 - Tell the system to use all device numbers.
4C - Identifies the model with which we wish to communicate. (In this case the MU80).
01 - Identifies the part and channel that we wish to modify.
24 - Identifies the modification we wish to make.
XX - The data associated with this modifier.
F7 - Informs the synth that the message is over.


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