What is a DI Box?

A DI box is a little device that lets you plug instruments like guitars and keyboards right into the fancy soundboards at a recording studio or a big concert. “DI” stands for “direct injection” or “direct input.” The main job of a DI box is to take the signal coming out of your instrument and change it so it works better with professional audio gear.

Instruments like electric guitars and basses, keyboards, and drum machines usually have “high impedance” outputs. That kind of signal is great for plugging into an amplifier, but it doesn’t travel well over long cables. It can pick up a lot of noise and interference. That’s where the DI box comes in.

How a DI Box Works

Inside the DI box, there’s a transformer. This transformer takes the high impedance signal and turns it into a “low impedance” signal. Low impedance signals can go down long cables without picking up much noise at all. They also don’t lose their strength over long distances. This is real important for big stages and studios.

But wait, there’s more! The transformer also “balances” the signal. Unbalanced signals, like the ones from a guitar, use one wire for the signal and one wire for the ground. Balanced signals use two wires for the signal and one for the ground. This helps cancel out any noise that gets into the cable.

So in short, a DI box takes an unbalanced, high impedance signal and turns it into a balanced, low impedance signal. This makes the signal a lot cleaner and stronger when it gets to the mixing board or recorder.

Types of DI Boxes

There are a couple main types of DI boxes you’ll see out there:

Passive DI Boxes

Passive DI boxes don’t need any power to work. They’re simple and reliable. The transformer inside does all the work of converting the signal. Passive DIs are great for instruments with strong outputs, like active basses and keyboards. They tend to have a really natural, transparent sound. The downside is they can suck away some high frequencies and dynamics from weaker signals like passive guitar pickups.

Active DI Boxes

Active DI boxes have electronics inside that need power to work. The power can come from a battery or from “phantom power” supplied by the mixing board. The electronics give the signal from your instrument a boost before it hits the transformer. This helps make up for the signal loss in passive DIs. Active DIs usually have a “pad” switch that lets you turn down really hot signals. They also often have a “ground lift” switch to help get rid of ground loop hums.

History of DI Boxes

DIs have been around in some form since the 1960s. In the early days of rock ‘n’ roll, engineers came up with DIs as a way to get the sound of electric basses and guitars right into the recording console. Before that, the only way to record these instruments was to mic up their amplifiers. That gave engineers less control over the sound.

Some say the first DI was made by a Los Angeles engineer named Bill Putnam, Sr. Putnam’s company Universal Audio went on to make some of the most legendary DIs in the business. On the other side of the pond, a London engineer named Dick Swettenham was cooking up his own DI designs. His company Electrosound Installations Ltd. supplied DI boxes to major recording studios like Olympic and Trident.

As pop music got more electronic in the 1970s and 80s, DIs became a must-have for plugging synthesizers and drum machines right into the board. Today, you’ll find DI boxes everywhere from bedroom studios to festival stages.

Key Features of DI Boxes

When you’re shopping for a DI box, there are a few key features to look out for:

Inputs and Outputs

Most DIs have a 1/4″ input for plugging in your instrument. The output is usually an XLR jack that lets you run a balanced cable to your mixer. Some DIs also have a 1/4″ “thru” jack that sends your unaltered signal to your amplifier.

Pad Switch

A pad switch lets you cut the level of your incoming signal, usually by 20dB or so. This is handy for really hot signals that might overload the DI’s input.

Ground Lift

A ground lift switch disconnects the ground pin on the XLR output. This can help get rid of ground loop hum that happens when there are multiple paths to ground in your setup.

Phantom Power

Active DIs need power to run their internal circuitry. Many can take “phantom power” supplied by the mixing board over the XLR cable. This is a 48V DC voltage that doesn’t affect the audio signal. If your board doesn’t have phantom power, you’ll need to use a battery to power your active DI.

Choosing the Right DI Box

So how do you know which DI is right for you? It really depends on what you’re plugging in and what kind of sound you’re going for.

If you’ve got a passive guitar or bass with traditional magnetic pickups, a passive DI might be all you need. They tend to have a really natural, vintage kind of tone. Just make sure your instrument has a strong enough output to drive the transformer.

For active basses, keyboards, and other high-output instruments, an active DI can give you a bit more headroom and flexibility. The built-in preamp can help boost weaker signals and the pad switch lets you tame hotter ones. Active DIs are also a good choice if you need to run really long cable distances, like on a big stage.

There are also special DIs made for specific instruments. For example, you can get DIs with built-in speaker emulation for plugging guitar amplifiers right into the board. Some keyboard DIs have stereo inputs and outputs for synths with left and right outputs.

At the end of the day, the right DI for you is the one that gives you the sound you want with the least hassle. It’s always a good idea to try a few different ones to see what works best with your particular setup.

Related Audio Tools

While DIs are a key tool for getting instruments into the mixer, they’re not the only bit of gear you might need. Here are a few other tools that often go hand-in-hand with DIs:

Preamps

A preamp boosts your signal to “line level” before it hits the main mixer channels. Many mixers have built-in preamps on each channel, but outboard preamps can offer higher quality and more character.

Reampers

A reamp box is like the opposite of a DI. It takes a line level signal and converts it back to a high impedance, unbalanced signal. This lets you send a recorded track back out to a guitar amp or effects pedal. Some DIs have a reamp function built-in.

Splitters

A splitter lets you take one input signal and send it to multiple outputs. This is handy if you need to send your instrument to both the mixer and your amplifier. Some splitters also have an “isolated” output that prevents ground loops.