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Direct Box Basics

What is a DI box?
A DI box aka Direct Inject or Direct box is a tool we use in the studio to bring a signal from an instrument (guitar, bass, keyboards) directly into our recording system.

An audio engineer (or home recording enthusiast) will use the DI box for silent recording, as a backup or to process along with a microphone on an amplifier.

The DI box typically has 3 input and output connections.

  1. 1/4″ TS instrument input – electric guitar or bass connects here
  2. XLR-M balanced output – connects to mic preamp
  3. 1/4″ TS Thru – Continues the input path to connect to an amplifier.

For example, the DI box would be connected between an electric bass and audio interface mic input. The clean bass signal can be recorded without the need for an amp.

The DI box has a few functions.

  1. Impedance change – The instrument circuit will react correctly as if it was connected to an amp, and the mic preamp on the other side of the box will react as if a mic was connected.
    Without this the tone would be wimpy.
  2. Level change – An electric guitar outputs a signal that is relatively low level but significantly higher than the average microphone. The DI box steps the signal down from instrument to mic level.
  3. Unbalanced to balanced connection – Changing the unbalanced guitar signal to balanced mic level allows much longer cable lengths without signal loss or noise.
  4. Pass through – The instrument signal is split and can be continued to an amplifier.

The Hi-Z/instrument input on your audio interface preamps do most of these functions well but a high quality DI box tends to work a bit better and allows you to split the signal to continue to pedals and amplifier.

DI Box options
There are a wide variety of DI boxes on the market today in passive, active, multi-channel, and vacuum tube designs.

A passive DI is just a transformer with a few jacks connected, it doesn’t require any power. The Radial JDI is a very popular professional Passive DI Box.

An active DI is a more complex design that requires phantom power (supplied by the mic preamp).
The Radial J48 and Countryman Type-85 are very popular professional Active DI Boxes.

Active or passive? Generally speaking, they both do the same job well. In specific uses or if you are looking for less transparency, one may type may be better than other.

There are also many designed specifically for bass recording with tone controls and overdrive or amp simulation circuitry.
The Radial Bassbone, Sansamp BDI, and MXR M-80 are excellent examples of Bass DI/Preamps.


  1. David Gann
    David Gann June 23, 2012

    Timely subject, I have been looking these over lately. I just finished Goodwyn’s Line2Amp project. Which would be the more transparent model, and the advantages of either model (JDI vs. J48) for home studio reamping? I’m trying to decide which to purchase. Many thanks, (Team Jon +5 points)

    Dave Gann

    • Jon
      Jon June 23, 2012

      Hi David
      I have a reamping article coming up in a few days.
      For reamping the most transparent would be an active DI into a transformerless preamp. Transformers (in passive DIs and preamps, and mics) slow down or round off the transient. This can be extremely subtle or not depending on the quality of the transformer.

      Sometimes you want that, but for reamping you’d probably want the initial DI capture to be transparent and color the sound of the mic on the amp during reamping.

      On the other hand, using quality gear I don’t think it’s worth stressing over which is most perfect as you’re going to get a good sound even doing the opposite of what I suggested.

      Speaking of Peterson’s kits. I hear he’s got a DI kit coming soon.

  2. Michael
    Michael June 25, 2012


    Useful post! Thanks.

    Question — when recording guitar through a mic preamp, you use the 1/4 inch TRS DI output into the TRS line input of the DAW/Recorder, right ? I heard once never to output from the DI XLR into the recorder/daw XLR input….why would that be ?

    Thanks !

    • admin
      admin June 25, 2012

      Usually the XLR inputs on a device are designed to accept a microphone signal and go though a preamp stage. Connecting a preamp here can be noisy or distorted.
      A TRS Line input on a device is not amplified (usually) because it is designed to accept a signal that has already been amplified up to line level.
      It can be confusing at times though with some professional gear using XLR for line level inputs and outputs.

      An external mic preamp should connect to your recording device through a line input.

      Another reason is that you want to avoid accidentally sending phantom power to any device other than a mic or active DI box. Phantom power is sent out the XLR inputs but not on TRS jacks.

      • Michael
        Michael June 25, 2012

        Thanks for the excellent…and lightning fast…reply.

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