Why Use A DI Box? Need-to-Knows

Why Use A DI Box? Need-to-Knows

26th May 2020 @ 13:13 | Matt Mccracken

Crucial for both live and studio, what is a DI Box?

The DI (Direct Injection) Box is one of the most useful, yet most misunderstood pieces of musical gear there is. Pretty much every stage and studio setup has one and if you use a relatively modern interface that will have one built-in as well.

But what is a DI Box and what does it do? In this article, we'll give you a breakdown of the (ahem) ins and outs on this critical piece of studio equipment...

It's all about balance...

Before we dive into DI, we need to know how balanced vs unbalanced cables work so we can understand why you'd need a DI Box in the first place.

An unbalanced cable is the most commonly found on stage and is your typical guitar cable with a wide variety of uses. Its technical name is a 'TS Cable' after the connectors it has, which stands for 'Tip' and 'Sleeve'. As you can see in the picture below, there's a black marking on the cable which is your 'Sleeve' along with the 'Tip' itself which match the two wires inside, a signal and a ground that transport your sound.

A typical, unbalanced instrument cable with 'Tip' and 'Sleeve'.

A balanced cable, more commonly found in studio applications is called a 'TRS Cable', which stands for Tip, Ring and Sleeve. As you can see in the picture below this balanced cable has two black markings underneath the tip, because a balanced cable has three wires to transport your signal, two signal wires ( called hot and cold) and one ground. This is the same for XLR cables, the only difference being the connector itself having a different format.

A balanced instrument cable with 'Tip', 'Ring' and 'Sleeve'.

So aside from the look, what's the difference? An unbalanced cable, because it only has one cable carrying the signal plus your ground wire, is more susceptible to noise because the cable acts as an antenna for interference. The ground wire does a decent job of noise reduction but only to a certain extent, which is why you'll be hard pushed to find an unbalanced cable longer than 20ft, as the noise level associated would become too much.

A balanced cable does the neat trick of cancelling any noise thanks to the hot and cold signal cables. Both send a signal, but one has its polarity reversed. Now bear with me here, if you have two signals, one with reverse polarity and one normal, what you actually get is silence because each signal cancels the other out (see image below). This is called Phase Inversion and is a common pitfall of recording in stereo.

We can't work with silence so the audio gear receiving the signal at the end of the chain flips the reversed signal back to its original orientation. The noise itself doesn't have its polarity reversed as it travels along the cable but is subject to the flip at the end of the chain, resulting in a strong, noise-free signal reaching your audio device. This may seem confusing, but for the purposes of this article, it's enough to know that balanced cables give you noise-free operation.

Why DI?

So after that brief sojourn into electronics, let's look at the DI Box itself. At its core the DI box is actually quite a simple device, it's what you can do with it that opens up a world of possibility. The essential function of a DI box is to convert a high-Z or high impedance signal to a low-Z or low impedance mic signal, but why would we want to do this?

Passive pickups on a guitar emit a high-Z signal, whereas gear that receives this signal such as mic preamps and mixing desks require a low-Z signal. The signals need to be at low-Z for recording and live purposes, thus the DI box ensures you get the right level signal for recording and the PA system.

The DI Box also allows you to split your signal, sending 'Wet' and 'Dry' signals to different places, which is why it's such a useful bit of studio and stage gear. On stage this allows you to send the balanced output to the desk whilst the unprocessed signal carries onto your amplifier. In the studio, you can record both effected and non-effected signals, which means you have the original signal available for re-amping or adding extra texture.

The third benefit of a DI Box is that it allows you to send your signal over longer distances without incurring any extra noise, which makes it fantastic for studio usage when you've got massive cable runs to amp rooms and audio gear.

Types of DI Box

There are two types of DI Box, Active and Passive and both have their uses depending on the situation you find yourself in. The primary difference between the two is that an Active DI Box is powered whereas a Passive DI is not.

Obviously there's more to it than that though! The rule of opposites occurs here, Active DI's work best with Passive instruments such as Electric Guitars and Passive Bass Guitars. This is because they utilise an active electronic buffer circuit to boost the signal, which is great for guitar work as an unamplified guitar signal can sound a little dead and lifeless.

Passive DI's work best with Active instruments like Keyboards, Active Bass Guitars and Electronic Drum Kits. A Passive DI has more headroom than an Active DI with a gain reduction of around 20 to 22dB. As these instruments tend to have onboard preamps with a 'hot' signal output, you don't need the amplification that an Active DI would provide.

Uses for DI Boxes

On Stage:

On stage you're far more likely to find Passive DI Boxes as most gigging musicians know, finding a free power socket on stage can be needle in a haystack type stuff. As a Passive DI doesn't require one, they're far more useful in this application. The nature of the transformer of a Passive DI Box also means that it's highly resistant to the dreaded Ground Loop Hum, as it eliminates any direct electrical connection between input and output so you get a noise-free operation which will do wonders for your live sound.

The Tom'sline Matchbox DI is great for guitars.

Bass Guitars:

DI Boxes are often used for Bass Guitars on stage and a common recording technique is to mix the DI with a mic signal recorded from the amplifier. You get the natural bass sound from the amp paired with the unaltered direct sound to add punch to your recordings. A DI'd bass tends to result in a clearer and more defined tone, which is what you want in the recording process and useful for live sound where rooms can be boomy or muddy.

EHX's Battalion is both Preamp and DI in one.

In the Studio:

Passive DI Boxes also have a nice-sounding natural saturation when driven hard which can result in a pleasant sound effect, whereas when Active DIs are pushed they result in a sound that's similar to digital clipping. Obviously having both Passive and Active DIs is a must for all studios as you encounter a wide variety of instruments with high and low impedance that need recording.

The Chord Active DI is a great studio addition.

Re-Amping:

Recording a DI signal during the recording phase means that the engineer can 'Re-Amp' your signal at a later date. You take the DI signal you captured during the original performance and use the 'Re-Amp' device to send it to a different amplifier and/or effects. This saves you time setting up that perfect guitar tone and lets you concentrate on getting a good take before returning to the tonal tweaking later on in the session.

In Conclusion...

So there you have it, DI Boxes are essential for any recording or live sound engineers and nowadays you'll find them built into pretty much every audio interface. So if you're starting to get serious about your home studio project or want to get set up for live sound, these ingenious little boxes are a must-have piece of kit and will ensure you get the highest quality recordings as well as being a versatile addition to any live sound setup.

If you liked that, then you'll like this

Our recent article we went through the process of "Re-amping using Laney amp heads".

We also went through the importance of DI boxes in our "Gigging Without an Amp"" article.

Get in touch

If you have a burning question that needs to be answered, then our Customer Service team can be reached via telephone on 01925 582420. Our in-store specialists will guide you through the what gear to utilise in you live or recording setup, just pop into your nearest Dawsons store.

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