DI boxes, sometimes referred to as direct boxes, which stands for us "Direct Injection," are some other most important pieces of studio gear, even though they often go undiscussed. 

So what exactly is a DI box, you ask? 

The main goal of a DI box is to take high impedance or unbalanced signals and convert them into signals that and being used for a microphone input on a console. People will use DI boxes in both the recording studio and in live performance situations. 

High-impedance or unbalanced instrument signals are those that are transmitted from many Electric pianos, pickups found on electric guitars and bases, and even a few older synths.

Do I Need a DI Box?

Knowing whether or not you need a DI box starts with getting a better understanding of how and why they were developed in the first place. 

Back in the day, the only things recorded with microphones were acoustic instruments. We'll call this the dawn of the recording arts. As time moved on, manufacturers began developing electronic instruments, such as electric guitars, and microphones were placed directly in front of sound source outputs (amplifiers). 

At some point or another, someone came up with the genius idea of bypassing the need to convert electrical signals into acoustic signals using a microphone and loudspeaker. They did so by using the electrical signal coming out of the electric sound source and directly injecting it into the mixing console. 

The only issue is that electrical signals found in musical instruments aren't compatible with microphone output signals, meaning they needed a special box to convert.

Essentially, if you want to send your electric signal from your sound source to an audio interface or mixing console, you'll need a DI box to do so. 

What's Going On Under the Hood?

The next question is, how do these little magic boxes function?

At its essence, a DI box has three unique functionalities.

Firstly, it translates electronic musical instrument output level, otherwise known as line level, to microphone level. Some examples of these instruments could include guitars, digital pianos, or synthesizers.

Secondly, a DI box is used to convert unbalanced output signals to balance output signals. Just about every electromagnetic instrument uses an unbalanced signal on the output, though microphones, for the most part, use balanced output levels.

Because most professional-grade audio equipment is manufactured to accept balanced signals or microphone-level signals, you typically have to convert unbalanced signals into balanced signals.

Lastly, DI boxes are made to reduce humming noise and ground loops, which can be especially problematic in older home studios.

Passive Vs. Active DI Box

When it comes to active and passive musical equipment, there's often a bit of confusion as to what path to take.

The quickest and simplest answer to whether you should get an active or passive DI box is that it depends on your power source. You have to look at the output level of the instrument you're trying to record. 

The golden rule is that if the sound source is an active sound source, such as an acoustic guitar with an integrated preamp or a keyboard, you can use a passive DI box. On the other hand, you'll need a DI box if you're using something like an electric guitar, a passive keyboard, such as a Rhodes, or an acoustic guitar with a passive pickup, such as a Piezo.

Things to Look for When Buying a DI Box

DI boxes have come a long way since they first came to fruition in the 1960s, and a quick online search will bring up results for hundreds of unique active and passive models with a wide range of distinct features. The versatility is seemingly endless. Let's look at a few specific features to look for when you're hunting for the right DI box.

Ground Lift Switch

Unbalanced instrument signals are notorious for having a fair amount of external noise, which is where DI boxes can be incredibly helpful. 

DI boxes with switchable ground lifts allow you to disconnect the '1' pin on the DI box's XLR jack, eliminating noise and breaking the ground Loop by preventing any current from moving along the shield between the DI and the mic pre.

Pad Switch

Many DI come with pads, which are gain attenuators that prevent internal circuitry from high-level overload. 

Pads usually come with a fixed gain reduction setting, somewhere between -15 and -20 dB, and they're great for reducing extreme output levels that come from unbalanced line-level devices and active pickups, including keyboards and some other digital instruments.

Thru/Bypass

The "Thru" switch, otherwise known as the switch, splits the input level into a separate quarter-inch output, so that the line-level signal can be sent to a PA, amplifier, or mixing console using a balanced XLR out. Having one of these switches on your DI can be particularly useful if you play bass in live situations. This is because you can separate the signal monitoring your sound on stage while drastically reducing the volume. 

Thru switches can vary in terms of functionality, as some are either buffered or completely passive. There are even some active DI boxes that are perfect for chains of effects pedals or long cable runs. 

Number of Inputs and Outputs

Another important thing to consider when picking out the DI box is how many inputs and outputs it has. Think of how many you'll require in your particular setup. 

For example, having a DI box with a single channel is more than enough if all you're looking to connect is a single-channel instrument, such as a guitar. On the other hand, if you're looking to connect a stereo-signal instrument, such as a keyboard or synthesizer, you'll need a DI box with multiple channels. 

Polarity Reverse

A polarity reverse switch flips the phase on a DI box, reversing pins 2 and 3 on the XLR cable. Recording Engineers will often use this as an effect, flipping line-level signals out of phase to produce unique effects. This can be an especially desirable tool for guitarists, especially for those who don't have access to phaser pedals. 

Polarity switches can be equally helpful in the live performance realm, as they can reduce the amount of feedback you get from an instrument.

Top 5 DI Boxes

Let's take a look at a few of the most popular DI boxes on the market today.

Radial Engineering Pro DI

One of the most popular manufacturers of DI boxes in the industry today is Radial Engineering.

The company Pro DI is a site to behold, using a 14-gauge steel chassis that's nearly indestructible. It's the perfect piece of equipment if you're looking for something that can handle a heavy touring or gigging schedule. Just as durable as the chassis is the group of switches, including the inputs and outputs, perfect for moving quickly from gig to gig. 

It also just so happens to have one of the best isolation ratings in the price range, so if you're doing professional recording sessions or live shows, I highly recommend it.

Countryman Type 85 Direct Box

The Countryman Type 85 Direct Box is a very unique choice in that it allows users to select either microphone or pickup settings, giving them greater control over how the signal is impacted by the device. 

Over the past decade, it has become somewhat of an industry standard, especially in the professional studio realm. With that said, it is quite pricey, so if you're just a weekend guitarist or hobby player, I might not recommend it.

Behringer Ultra-DI DI1400P

Behringer is one of the most well-known musical instrument and hardware developers on the market today, offering some of the best budget-friendly equipment money can buy. The beauty of the Ultra-DI DI400P is that it works really well for long cable runs, reducing hum without suppressing high-end frequency content. 

One of the main drawbacks of DI box, however, is that the ground-lift switch isn't the highest quality and may not isolate as well as some other pro-grade DI boxes. 

Because of this, it's much better for live performance applications rather than studio recording.

Tech 21 Para Driver V2

The Tech 21 Para Driver V2 might be one of the most distinct DI boxes on this list, as it was made for a very particular purpose. That purpose was to influence the tone of the input instrument. If you want to get a little bit of drive or warmth on your input signal, it's one of the best DI boxes on the market. 

On the other hand, if coloration is not what you're looking for, I would look elsewhere.

Whirlwind IMP 2

One of my favorite DI boxes for budget-conscious musicians and engineers is the Whirlwind USA IMP 2. It does an excellent job of reducing hum and unwanted noise, especially during studio recording situations. Even for the price, the ground-lift switch isolates really well. Plus, similar to the Radial Engineering Pro DI, it's built like a tank.

Direct To The Source

If you're a recording musician or a live sound engineer, having a DI box that your disposal is incredibly important. It's also worth noting that most modern audio interfaces have them built in already, though if you're getting serious about your current setup, we recommend looking into whether or not you need to integrate one.