MIDI (Musical Instrument Digital Interface) is a system invented in the late 1970s that allows musical instruments to transfer digital data between each other and where necessary operate as a master or slave controller unit. To do this each instrument must be equipped with a MIDI interface that consists of three options - MIDI In, MIDI Out and MIDI Thru.
The cables that connect these interfaces are known as MIDI cables and are in fact five PIN DIN cables but with only three of the pins connected (which is why five PIN DIN audio cables cannot be used). The original MIDI specification stipulates that 15 metres is the longest length permissible for these cables and any attempt to run longer will cause data corruption and drop-outs. MIDI cables are plugged IN to OUT and OUT to IN or OUT to THRU depending on what you are trying to achieve with the connectivity.
