Home Recording: 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.k.a., a piece of equipment) to a low impedance mic level balanced input, usually via XLR connector. The DI performs level matching, balancing, and either active buffering or passive impedance bridging to minimize noise, distortion, and ground loops. DI (pronounced dee EYE, not “DIE” as in “die feedback, die!”) is variously claimed to stand for direct input, direct injection or direct interface. The ends of each coil of wire protrude from the windings; one pair of ends is the input, and the other pair is the output. If the primary has more windings than the secondary, it is called a step-down transformer because the signal level and impedance are lower at the output than they are at the input. Passive DI Units A passive DI unit typically consists of an audio transformer used as a balun.
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Church Sound: Passive & Active Direct Boxes, And How They Should Be Used