Can You Use a DI Box in Reverse?

There are countless arguments both for and against using a DI box in reverse. Without a doubt, a DI box comes in handy by transforming unbalanced signals to balanced, producing clean, distortion-free audio. But do you see those same results if you connect your DI box in reverse?

You can use a passive DI box in reverse. However, the reproduced sound will have plenty of distortion and noises, ruining your listening experience. Avoid such dirty sound by using an attenuator, like an H-pad, which reduces the signal level of the output, producing crisp sound.

Read on for more information on the function of a DI box, types of DI boxes, and how to reduce the output signal level when using this device in reverse.

DI Box from Radial Engineering
A great passive direct box from Radial Engineering.

What Is a DI Box and Why Do I Need One?

A direct injection (DI) box, also called a direct box, is an electronic device that converts high impedance signals to low impedance signals. It allows you to connect musical instruments to the mixing board during audio production without distorting the sound signals.

When using electronic musical instruments, there will almost certainly be some electrical resistance (unbalanced high-impedance audio). This may lead to signal degradation, causing undesired noise. However, balanced wires with low resistance (low impedance) tend to produce less noise.

To achieve clean sound reproduction, audio engineers need to convert the high impedance signals from a musical instrument’s cable to a low-impedance signal that can run into the mixing board without degrading the signal. That’s where a DI box comes in handy.

Active vs. Passive: What Are the Differences?

Although DI boxes come in different shapes and sizes, they can be either active or passive. In the simplest terms, an active direct box requires power to function. You can power it with a battery, a phantom power source, or a dedicated AC supply. The Radial J48 is an example of this type of DI box.

Conversely, a passive direct injection box doesn’t need a power source to function; it acts as a transformer. The Radial JDI is a popular example of a great passive direct box.

Are DI Boxes Bi-Directional?

In other words, is a direct box a two-device solution? Can you use it as a reamp?

As we mentioned earlier, you can use a passive DI box in reverse. Using this type of device for reamping isn’t new. Steely Dan, the Beatles, and Les Paul are examples of artists who’ve used DI boxes in reverse.

For example, say you want to reamp a heavy guitar using a passive DI box. In that scenario, you’d follow these steps:

  1. Plug the guitar into the direct injection box and send the throughput to the guitar amp.
  2. Connect the balanced output on the DI box directly to the mixer and record a clean guitar track.
  3. Place a mic in front of the guitar amp in the usual way, and then record another track.
  4. Take the clean guitar track you initially recorded and send it back through the DI in reverse by connecting your mixer’s output to the DI box XLR output.
  5. Ensure the mixing board’s output level is low to prevent saturating the transformer, which would distort sound signals.
  6. Now, connect the input on your DI box to the guitar amp or effect pedals inputs.

You may think, “Great! I’ll take my DI box and run it in reverse now!”

Not so fast!

When you connect a DI box in reverse, you’ll likely hear several distortions and noises in the reproduced sound. Let’s describe how that occurs using a hypothetical scenario:

DI Box in Reverse: A Hypothetical Scenario

Assume you have a DI box that can convert a signal from 1-milliohm impedance and -20dBu decibels to a 1.5-kiloohm impedance and -30dbU. Now, suppose you have a line output of 600 ohms and OdBu. In that scenario, the input signal would be significantly hotter than the expected output.

Alternatively, let’s assume you’re running the DI box the usual way and stepping down a ratio of 4:1. That would be about -12dB. If you try going from a -20dBu guitar signal to a 30dBu mic signal, the -12dBu will give you -32dBu, which would be quite nice.

However, by running your direct injector box in reverse, you’d be increasing the voltage by 1:4, giving you +12dBu. Now, say your line outputs are already outputting +2.21dBu. If that’s the case, the reverse box will increase the level to +14.21dBu, which is already higher than the -20dBu your guitar’s amp expects. Therefore, you’d have a massive output signal level!

To lower the output signal, you can reduce your sound card or mixer’s interface. However, that reduces the bit depth and degrades the signal. And, that may not be a practical solution since the output has a fixed noise floor. As a result, you’d only be raising the signal-to-noise ratio.

So, how do you fix this problem so that your passive DI can work in reverse? 

The solution is to use an attenuator, such as an H-pad.

How To Attenuate Signals With a DI Box in Reverse

In a nutshell, an attenuator reduces the intensity of a signal. Most notably, it’s used by audio engineers to reduce a signal’s level, preventing overload and distortion.

To minimize the distortions arising from connecting your DI box in reverse, you need the following:

  • An H-pad
  • A sound level (SPL) meter
  • Your DI box
  • A splitter (optional; most DI boxes come with a throughput)
  • XLR, splitter, and SPL meter cables
  • A meter plug-in for your digital audio workstation (DAW)

Once you’ve gathered these tools, you can attenuate the signals with or without a splitter.

With a Splitter

You can record the direct guitar signal and its amplified version with a splitter, then match the reamped level to the original amp recording. The entire process takes place in the DAW.

To do that, follow these steps:

  1. Record the direct signal and the microphone version from your amp.
  2. Place the meter plug-in on the recorded amp signals in the DAW.
  3. Press play in the DAW.

Reamp Stage

Follow the steps below:

  1. With input monitoring on, create a track that takes input from your mic.
  2. Set up the direct signal output to your amp and press play in your DAW.
  3. Adjust your output track’s level until the input track from your amp matches the level you noted when testing the recorded amp version.
  4. Press record!

Note: If you do this correctly, the original and the new recording levels will be the same, and they’ll sound similar.

Without a Splitter

You can use an SPL meter to attenuate signals without a splitter. To use this method, record the direct signal.

Reamp Stage

Follow the steps below:

  1. Set up the amp for recording.
  2. Plug in your guitar and play a sound similar to what you’ll be recording.
  3. Using the SPL meter, note the sound level.
  4. Create a new track that takes input from your mic.
  5. Set up the direct signal output to the amp.
  6. Modify the level of the output track so that the amp and SPL levels are similar to when you initially recorded the guitar sound.
  7. Press record!

Your final results should be the same as those you’d get using a splitter.

Bottom Line

A passive DI box is bidirectional; you can use it in both forward and backward configurations. However, it’s critical to check the signal levels. Most notably, connecting your DI box in reverse offers a large signal boost. As a result, you’ll wind up with distorted, extremely loud sounds. However, you can use an attenuator to reduce the intensity of the boosted sounds, getting a cleaner, pleasant sound that matches the original.