There are three common questions folks ask us when considering a direct box:

1. Do I actually need one?
2. What kind of DI should I get?
3. How much should I spend?

Do I really need a DI box?

The answer is 'it depends'. A direct box is primarily used to allow you to run a long cable without adding noise or losing signal quality. High impedance signals tend to be much more prone to noise and keeping cable lengths under 8 meters (25 ft) is recommended. A DI box converts the high-impedance of an instrument to a balanced low impedance signal. This enables the instrument signal to travel distances of 100 meters (300 feet) without adding appreciable noise. The output of a DI box is mic level – thus the balanced signal is treated just like a microphone.

When playing live, the mixing desk is usually positioned in the house (front of house or FOH position) which is often 50 to 100 meters away. Most instruments such as bass guitar, acoustic guitar and keyboards are connected to a DI box and mixed at FOH. For the sound engineer, capturing the sound before it is processed by the artist on stage usually makes it easier to amplify the signal as it can be optimized for the room.

In the studio, recording from a separate room (isolation booth) enables the engineer to capture a direct sound from the instrument using a direct box and also add a mic in front of the amplifier to capture the tone generated by the amp. When recording in the control room, you may or may not need a DI box, depending on the tone you are looking for. Most mixer inputs have a 'one size fits all' type of input that may not flatter your instrument. A good DI box is optimized to interface with your mixing desk or recording system by presenting the instrument with the right input impedance. This can take the edge off the instrument for a smoother, more natural sound.

What kind of DI box should I get?

This is like asking what kind of microphone should I buy. Just as there are all kinds of microphones for all types of applications, there are a number of DI box types for the same reason. Just as you could use a dynamic microphone like a Shure SM58 to capture just about anything, you could buy a Radial JDI and be pretty much set. But sometimes, using a condenser mic can give you the extra reach to capture more sparkle from an acoustic guitar or more detail from a voice when recording. An active DI box like the Radial J48 is almost the same.

Like dynamic microphones, passive DI boxes tend to be able to handle more signal level without distortion while condenser mics – like active DIs - generally produce a wider frequency response while being more sensitive. And just as most studios and live stages are equipped with a selection of dynamic and condenser mics, both passive and active DI boxes are often used side by side. The choice usually comes down to personal preference.

A simple rule of thumb:

1. If the source is active, use a passive DI box
2. If the source is passive, use an active DI box

So if you have an old Fender Precision bass with magnetic pickups, an active DI box will probably work best as the buffer will generate plenty of signal for the PA system while reducing the load on the instrument. If on the other hand you have a new, high output active bass with a 9 volt battery inside, you can turn up your volume with confidence knowing that your passive Radial ProDI will easily handle the signal without distortion.

Over the years, industry standards become common place. For instance, most engineers prefer to run an acoustic guitar through an active DI like the Radial J48. On AC powered devices like keyboards, electronic drums, DJ mixers and other active sources, most engineers prefer to use a passive DI like the Radial ProD2. This is because passive DIs can handle more level without distortion and they are also really helpful when it comes to eliminating hum and buzz caused by ground loops.

How much should I spend on a DI box?

We recommend that you follow the 5:1 rule: if you spend €1000 on an instrument, you should probably invest €200 in a direct box. So if your guitar is worth €500, sending €100 on a direct box is probably the right ratio. In our view, there is no point in spending €200 on a DI box if your guitar is only worth €200.

Think of it this way: would you spend €2000 on a great guitar only to play through a €30 guitar amp? Probably not. A DI box is a unity gain preamp. Preamps can cost anywhere from €30 to €10,000. And just like guitars, basses, keyboards and studio preamps - direct boxes come in all shapes, sizes and quality levels based on your expectations. There is no shortcut to quality. Radial DIs are used on the world's top stages and in the best studios because they are designed to deliver the utmost quality day in and day out. We are confident that once you listen to the difference, you will come to appreciate the benefits.

Radial DI boxes come with a 3-year transferable warranty which means that if you decide to sell your Radial DI within the warranty period, the warranty will still be good for the next owner. And because Radial DIs are in demand, they tend to have a much higher resale value.

As described above there are no hard fast rules. It comes down to taste and application.

On this roadmap you can find out which DI is most suitable for your instrument.

Comparing passive DIs for instruments

Comparing active DIs for instruments

Comparing DI boxes for the studio