Often abbreviated DI (for direct insertion), a device commonly used to convert high impedance (see WFTD archive Impedance) unbalanced signals from a stage instrument (like a bass or keyboard) into a low impedance balanced signals. This puts the signal at the proper voltage level for the mixer and prevents the instrument from becoming loaded down with too low impedance, which could cause tonal shifts and distortion. It also allows the signal to be transmitted over long lengths of cable. They are always used in live sound to get a signal out of an instrument on stage out to the mixing board, which can be as much as 500 feet away. A simple direct box consists only of a small transformer, but more sophisticated designs employ electronic gain stages that more closely resemble the input section of a modern instrument amp. They may also have some combination of ground lift switches, equalization switches, level matching switches, isolated line outputs, and more.