Over the last few years, I’ve been getting questions about DI boxes.
What are they? What do they do? Are they necessary for my setup?
In this article, I’ll take a couple of minutes to explain how they work, how they can help your recordings and whether you actually need them in your music production setup.
Let’s jump right in.
What is a DI Box?
D.I. stands for Direct Injection or Direct Insertion.
In audio work, Direct Injection refers to the process of capturing a signal without the use of a microphone.
You do not pass the signal through the air, so it does not suffer from degradation while being transferred. That means you don’t get external (room) noise in your signal that might be difficult to remove later.
Why Use a DI Box?
A DI box is a pretty handy piece of kit.
We’re going to get into the weeds with some of the terms here but I feel this are important concepts to understand.
#1 — It Fixes Interference Issues (Signal Balancing)
If you are recording in an environment with a lot of radio frequency interference, old a place with bad electricity, this can affect your audio signal.
A DI box converts a high impedance unbalanced signal to a low impedance balanced signal and then send that through a balanced microphone cable. A balanced 3-pin XLR mic cable is less susceptible to interference than instrument cables.
A Balanced vs An Unbalanced Signal
A balanced signal has three legs — a common ground, a positive leg, and a negative leg. An unbalanced signal has only two legs — a ground and a hot.
The difference is application between the two types is that a balanced signal can be transmitted much longer without the risk of outside inteference or signal degradation.
Unbalanced signals are less complicated but are more suspectible to noise problems and inteference.
For example, an unbalanced signal such as that from a passive guitar cab typically only be transmitted 5 meters of 15 feet before you run the risk of outside inteference, hums, buzzes, and in extreme cases RF inteference.
Another signal inteference problem a DI box fixes is ground loops.
What is a ground loop?
An ground loop (or earth loop) is when two points of a circuit intended to have the same ground reference potential have different potential between them, usually as a result of enough current flowing in the ground to cause this.
Ground loops are a major cause of noise, hum, and interference in audio.
That’s where a DI box comes in. Should there be a problem with your electricity, a DI box will stop a ground loop from starting and generating a 50 or 60 cycle hump.
Note however that if you have noisy pickup, the DI box will not fix that because mic cables only keep additional inteference from getting to the signal as it travels through.
The DI box does not take any noise out of the signal that’s being fed directly from the source.
#2 — It Fixes Impedance Issues (Impedance Matching)
In the last point above we mentioned high vs low impedance.
Let’s take a minute to explain what that is and what you should be looking for in the specs of your interfaces and your DI boxes.
What is impedance?
Impedance is simply the opposition a circuit presents to a current when voltage is applied. It is basically AC resistance.
Here’s the bit you need to really pay attention…
Without getting overly technical, it’s important to understand that all instruments, whether they be guitars, keyboards, pianos, and so on, have what’s called output impedance.
That impedance is the electrical resistance of the circuit that’s outputting the signal from the instrument.
That’s either high impedance or low impedance.
For the best sound quality and voltage transfer, the input impedance of the connector you’re plugging into, such as your audio interface, should be roughly x7 or x10 higher than the output impedance of your source, such as your guitar.
For instance, the output impedance of a typical electric guitar is ~ 20-40k Ω, so the ideal input impedance of your guitar amp, your DI box, or your audio interface should be ~ 280k-400k Ω, on the higher side.
If you connect a low impedance source, into a high impedance load, you won’t have any distortion or frequency response change because of this connection.
But on the other hand…
Instruments that do not have an onboard pre-amp (there is no battery in the instrument) have a relatively high output impedance.
If you connect a high impedance source, into a low impedance load, you will have distortion or frequency response change.
This high frequency loss, or response change, or distortion is due to a mismatch between the impedances.
This is they type of thing you need to check on your device specifications.
These days, most audio interfaces have instrument inputs as well as mic inputs.
For instance, although FocusRite’s Scarlett 2i2 has a mic input impedance of 3k Ω, it has an instrument input impedance of 1.5M Ω, that more than takes care of this issue.
If your interface or your mixer only has mic level inputs, you will have to get a DI box to make that work. A typical mic input has as input impedance of 1.5-3k Ω.
One of the things that a DI box does is provide a relatively high input impedance so that you do not encounter this high frequency loss.
A DI box such as the BSS Audio AR-133 Active D.I. Box has an input impedance of 1M Ω. This will provide correct impedance matching between your instrument and the interface, mixer or recording system.
#3 — It Prepares a Signal for Re-amping
This point also ties into the first point we talked about — inteference.
What is Re-amping?
In multitracking, re-amping is routing a recorded signal out of the editing environment through to external processing using effects before sending that signal back to a guitar amp.
Here’s the thing to keep in mind.
When you are re-amping, you want to the send the cleanest sound possible to your amplifier.
So if you have an inteference issue, such a ground loop issue that’s generating a 50 or 60 cycle hump in your signal, you don’t want to send that to your amp while recording.
A di-box helps remove inteference when issues that might cause problems with re-amping.
#4 — It Helps in Editing a Live Amp Recording
When you record with live amps it can be very difficult to edit just the live amp recording. This is because the transients and high distortion tones are almost visually indistinguishable.
If you know that you will need to edit the live recordings after, record the di box also. This will give you a nice visual reference when editing later.
Is a DI Box Necessary For Your Setup? When Do You Need a DI Box?
Now comes the big question—
Do you need a DI box?
If you run a home studio, and you’re making music you personally distribute (meaning you likely won’t re-amp) — probably not.
It’s easier to just plug in directly into your input on your interface, and that gets great quality music.
If you don’t need the re-amping later on, don’t worry about it.
However, if you’re looking to re-amp later, if you want to break a ground loop, or you want to send the cleanest signal possible to a mix engineer so they can re-amp — then yes, DI box would be worth the investment.
Also, as I mentioned earlier if you need to run an unbalanced signal more than 5 meters or 15 feet, you need a DI box because you need to convert that unbalanced signal to a balanced signal in order to avoid signal interference and degradation.
#1 — It Helps with Connector Matching
If you play guitar or keyboard, you already know that your instrument outputs on Jack connector. Most interfaces and mixers input a 3-pin XLR connector.
A DI box has Jack input connectors on one side where you plug in your Guitar or Keyboard and a 3-pin XLR output on the other.
That another thing a DI box can do.
You should now have a clear idea of what a DI box is, why you would need one and if you need to.
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