The role of the D.I. box is often misunderstood. So here's a quick guide.
D.I. stands for direct injection. In other words inputting the signal of an instrument into a live (or studio) mixing console without the use of a microphone. But the problem with most instruments such as keyboards, drum machines, acoustic guitar pickups, etc is that their output signal is unbalanced. Therefore the primary role of a D.I. box is as a balancing interface. Converting the unbalanced signal from high level instruments such as keyboards, drum machines and even on stage DJ or sub mixers, into a balanced signal that can be safely sent down a stage multicore cable and into the balanced input of a mixing console without interferance from or interering with other channels.