What does a DI box do? Why use one?

What does a DI box do? Why use one?

A direct injection (DI) box converts unbalanced instrument level signals with high impedance (electrical resistance) into balanced microphone-level signals with low impedance.

The pick-ups on instruments such as electric guitars and bass produce a signal with high impedance, but we need to decrease the resistance via a DI box so we can run these signals through a mixing desk.

  • What does a DI Box do?
  • Do I need a DI Box for home recording?
    • But in a professional studio…
  • How does a DI Box work?
    • What does a passive di box do?
    • What does an active DI box do?
  • What’s the difference between active and passive DI boxes?
  • Common features you’ll find on a DI Box

You’ll usually find DI boxes on stage during a performance, though you can use them in your home recording studio. However, the reason you’ll see them on stages more than in studios is due to how unbalanced signals pick up noise over longer distances.

The point of a direct injection box is to convert an unbalanced signal to a balanced one while it travels through a long cable. So converting that unbalanced signal into a balanced one via a DI box eliminates the noise problem. As a result, DI boxes come in handy in larger venues on big stages with big PA systems. In fact, one DI box allows the signal to travel a distance of 100 meters (300 feet) without picking up noise! And a live mixing console is usually positioned 50 to 100 meters away from the performers. So a DI Box is a critical tool that sits between them that keeps the signal from bass and electric guitars and keyboards/synths clean as it travels to the mixing desk.

audio interface will have at least one microphone preamp built-in. This means you do not need a DI box to record with a microphone in your home studio as your audio interface does the same job.

As for instrument-level signals, audio interfaces have dedicated instrument inputs in the form of 1/4″ inputs that have a high impedance to match. Hypothetically, if you were to connect a high impedance instrument signal to a low impedance input you’ll chop off some high-frequency content which isn’t very desirable. But thanks to the manufacturers of audio interfaces, this won’t happen!

So no, you do not need a DI box for home recording if you have an audio interface.

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But in a professional studio…

In contrast, you may find DI boxes in high-end recording studios. This is because instrumentalists record in an isolation booth which allows the microphone to capture the direct sound from the instrument with no background noise.

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What does a passive di box do?

Passive DI boxes are the most common DI boxes you’ll find. Passive DI boxes work best for headphones or loudspeaker outputs. But a common problem you’ll encounter with passive DI boxes is hum. Typically, cheaper DI boxes have a more noticeable hum. Additionally, passive DI boxes aren’t as versatile as active DI Boxes.

However, passive DI boxes do not need an external power source to work. They’re also easy to use and durable, and the high-end passive boxes are very reliable.

The Behringer Ultra-DI DI400P is a affordable example of an passive DI box. It's not got so many features as other DI's, but it does capture a harmonically rich sound - making it a great choice to record/perform with electric guitars, bass, keyboards, and synths. It also features a ground lift switch to cancel out ground loops.
The Behringer Ultra-DI DI400P passive DI box. Image Credit: Behringer

The Behringer Ultra-DI DI400P is an affordable example of a passive DI box. It’s not got so many features as other DI’s, but it does capture a harmonically rich sound – making it a great choice to record/perform with electric guitars, bass, keyboards, and synths. It also features a ground lift switch to cancel out ground loops.

amplifier or to a monitor so you can hear your performance before applying external processing.

Ground lift

Balanced equipment can fall victim to the noisy hum and buzz that ground loops cause. So a ground lift option disconnects pin 1 of the DI boxes’ XLR input. This stops the current that flows between your DI box and microphone preamp and removes the noise.


Pads, which you’ll also find on some microphones, are gain attenuators that stop excessive gain from overloading the circuitry in the DI box. Pads often attenuate your signal by a fixed amount – such as 10 dB, 15 dB or 20 dB – and allow you to plug in equipment with high output levels and/or unbalanced line equipment.

Polarity reverse

Finally, we have Polarity reverse which flips the polarity of a signal and prevents feedback. If your mixer doesn’t have any polarity reverse options, one on a DI box is very handy.

Other applications of polarity reverse allow us to adjust the XLR cable configuration from a standard Pin 2 hot to Pin 3 hot. If you’re using an XLR cable that’s been wired incorrectly, polarity reverse will solve that problem while you use it.

And polarity reverse allows us to align the absolute polarity of a direct signal with the polarity of a microphone on the same input source. and keep the signal chain balanced

Final thoughts

A DI box is a critical tool in some scenarios. You can use them practically in live sound and studio applications. However, there is scope to use them creatively.

In fact, industry standards for DI boxes have grown. You may find that running an acoustic guitar through an active DI box may give your signal some desirable openness. But on the other hand, using a passive DI box with powered devices such as a keyboard or digital drums is better because a passive DI box can handle higher levels without distorting.

So, is a DI box right for you?

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