What does SysEx mean, and what does it do?
SysEx stands for System Exclusive (message). It’s a special kind of MIDI message (event) meant for a specific MIDI device. It therefore has some sort of address included, so when a SysEx message is transmitted, only the addressed device will act upon the content of the message. What you need to know is that a ‘normal’ MIDI message has a fixed length. This means when a message starts (with a specific byte), the hooked-up synthesizer automatically knows when this message ends. This is not the case with SysEx messages; they can vary in length. Therefore they need more than a specific start-marker (byte) at the beginning to indicate the start of a SysEx message, they also must have an end-marker. In between these two markers, any number of data bytes may be sent. That’s why SysEx messages need the end-marker. If it’s not clear right from the start, what the length of the message will be, then the end must also be marked. This is important for the addressed device that has to know what data
