Atelier der Tonkunst

The purpose of a DI-Box is the "interfacing" of musical instruments or other signal sources to the "microphone" format of a mixing desk. To do so, it provides three major technical aspects:

First: It provides balancing to unbalanced signals

Microphone signal lines are balanced and therefore have great immunity of catching distorting signals than unbalanced signal lines.

Second: It provides galvanic isolation between source and mixer

Galvanic isolation eliminates ground-loop distortion noises without compromising electric safety standards like chassis grounding of the involved equipment.

Third: It provides impedance matching between the instrument and mic input

Microphone lines are not only balanced, but also terminated with a low ohmic resistance like 2 kiloohms, or less. Musical instruments are terminated with significantly higher values, like 100 kiloohms to 1 megohm.

This matching is achieved by up-transforming the the microphone lines terminating impedance typically by the factor of 100. This impedance transformation comes along with a level down-transformation, typically by 1/10.

Since microphone inputs are very sensitive and feature a lot of low noise amplification this is an ideal combination to perfectly match instruments to mixing desks without adding any noise, distortion & coloration from an "actice" device.