A DI unit, DI box, Direct Box or simply DI is an electronic device that connects a high impedance line level signal that has an unbalanced output (a.ka. a piece of equipment) to a low impedance mic level balanced input, usually via XLR connector. DIs are frequently used to connect an electric guitar, electronic piano, or electric bass to a mixing console's microphone input.

The DI performs level matching, balancing, and either active buffering or passive impedance bridging to minimize noise, distortion, and ground loops. DIs do not perform impedance matching.  read more »