Understanding Direct Boxes: PART 1

Names

A Direct Box goes by many names:

  • DI
  • Direct box
  • Direct input
  • Direct insert
  • Direct injection
  • Direct interface

Source Types

Whatever name you choose to use, this little box performs several vital functions to achieve quality audio performance from your instruments and sound system. The direct box is most commonly used to connect unbalanced instruments like bass and electric guitars as well as electronic keyboards to a sound system. Other less common sources that can benefit from a DI are:

  • Acoustic Instruments with pickups
  • Electronic drums
  • iPods, MP3 players, and Smartphones
  • Unbalanced CD/DVD players
  • Computer audio outputs

Optimized Performance

The DI serves three primary roles in optimizing audio performance in your instruments:

  • Converts Unbalanced to Balanced
  • Impedance Matching
  • Level Matching

The direct box converts a high impedance, unbalanced instrument level signal to low impedance, balanced mic level signal.

Unbalanced to Balanced

One of the primary functions of the DI is to take the unbalanced signal from these sources and convert it to a balanced signal. This balanced signal can then be plugged into a standard microphone input on a stage snake or mixing consoles microphone preamplifier.

Balanced signal connections offer greater rejection of noise that can be introduced to the system over lengthy cables runs such as common stage snakes.

High Impedance to Low Impedance

Electrical impedance is the resistance to the flow of electricity in a circuit. These unbalanced instrument sources are high impedance signals.

High impedance signals tend to become dull, losing high frequency detail when traveling cable lengths over 15 - 20 feet. Using a short instrument cable to a DI can make an eye-opening difference to the tone of your instrument through a sound system!

Level Matching

The final transformation that the direct box performs is level matching the signal to the microphone input of your mixer.

Microphone signals are very low level signals, by contrast instrument level sources are higher in signal strength. A direct box allows you to plug in an instrument level signal into the microphone preamplifier of a mixing console.

Conclusion

The direct box plays an important role in providing noise free, high quality audio from instrument level sources on stage to the console at mix position.

With few exceptions, most DIs employ a transformer to accomplish their audio magic. The results are directly related to the quality of the transformer used. Well-constructed DIs can last several decades, so we suggest spending the money to get quality results for decades to come.

Circle City Audio proudly recommends DIs from:

  • Countryman Associates
  • Radial Engineering
  • Whirlwind

If you would like to purchase some new direct boxes for your system give us a call. We would be delighted to to help find the right product for your needs.