Direct boxes are often referred to as "DI" boxes. This stands for "Direct Injection" as their main purpose is to convert unbalanced and/or high impedance instrument signals into a format suitable for direct connection to a mixing console - without the use of a microphone.

In 1981, Whirlwind developed and produced the first commercially available Direct Box in the audio industry.

Read about it here.

A DI performs several functions:

• It converts a high impedance signal to a low impedance signal (although it will also accept a low impedance signal from a preamp, keyboard, active pickup or other electronic device).
• It converts an unbalanced signal to balanced.
• It reduces a strong instrument or line level signal (and sometimes even speaker level signal) to a mic level signal suitable for connection to the mic input of a mixing console.
• It isolates electronic equipment on stage from the mixing console, which can help eliminate interference and noise caused by DC interaction or ground loops.

Read more about DIs in our tech article: