Abbreviation for Direct Inject Box, the DI box is a piece of studio equipment for converting unbalanced musical instrument signals into balanced signals suitable for transmission over long wires and feeding into mixers and other pro kit.

Typically a small box with a jack socket input and "pass-through" output, an XLR balanced output socket, a power switch and an attenuation switch for matching the box gain to the instrument level.

Internal circuitry is a buffer amp and a balanced line driver, which may consist of a transformer or a solid-state impedance-converter.

Usually powered by internal battery, mains adaptor or some form of phantom power over the balanced line.