What are DI Boxes? (Types, Benefits, Uses)

The ‘DI’ in DI boxes refers to multiple names like Direct Insertion, Direct Injection, Direct Input, or Direct Interface. Fundamentally, DI boxes are used to take an unbalanced, high impedance signal and convert it to a balanced, low impedance signal.

Unbalanced signals are prone to noise. Hence, it’s important to convert that unbalanced signal to low impedance, balanced signal, especially while running signals over large distances. This is extremely helpful at larger venues with bigger stages and PA systems.

With the help of a DI, such issues can be resolved. A DI box ensures that the impedance matches the signal strength, thus the device functions well. The low impedance signal is better at rejecting noise, making it easy to use with devices such as mixers or speakers.

Types of DI boxes

Passive DI boxes

Passive DI boxes are the most commonly used DI boxes. They consist of a resistive load, either with or without capacitor coupling. Such units work best for outputs that are designed for headphones or loudspeakers.

Hum is a common problem encountered with Passive DI boxes. Typically, the cheaper the DI box, the more the hum will be noticeable. Passive units are also less versatile than their active counterparts are.

That being said, they are often preferred in certain situations because they do not require a power source (phantom power). Furthermore, they are quite simple to use, hardwearing, and the top shelf units are extremely reliable.

Active DI boxes

Active DI units contain a preamp section too. They have the ability to provide gain, are more complex and yet more versatile as compared to Passive DI units. However, active units require a power source.

This can be a battery or a standard AC outlet connection. Some active units also contain the option for phantom power use.

Most DI units have switches for important features like gain adjustment, ground lift, mono/stereo mode, and power source selection. The bypass feature is more commonly found in active DI units than Passive ones. The ways in which bypass occurs can be loosely classified into two ways.

In “True bypass”, the signal goes straight from the input jack to the output jack without involvement of circuitry or impedance from the source. False bypass occurs when the signal is routed through the circuitry without any intentional signal alteration.

The Key Differences Between Active and Passive DI Boxes:

The most basic difference between an Active DI box and a Passive DI box is that the latter doesn’t need a power source. Batteries or phantom power usually works with Active DI boxes. Among some of the more detailed differences, Passive DI boxes are merely transformers; they contain transformers to perform impedance matching and balancing.

The strength of the impedance signal always depends on the source. This could end up becoming a disadvantage if the source signal is particularly low level. This is because the DI box will not be able to do anything to increase the level of the signal.

However, the following are some notable advantages to Passive DI boxes:

  • No noise added due to active circuits

  • No power source required

  • Desirable coloration from the transformer

In contrast, Active DI boxes include a preamp unit. This provides a stronger signal and higher input impedance. It can sound good with lower level signals too. Tone-wise, certain Active DI units are designed to be extremely quiet, hi-fi, and transparent.

When Do We Require Active/Passive DI boxes?

Choosing a DI box is no different than choosing any other audio equipment; it all depends on the kind of sound you prefer. Generally, the sound produced by Passive DI boxes will be more rounded as opposed to an Active unit, which will produce a more high frequency tone.

What instruments work best with Active/Passive DI boxes?

Active DI units work best for direct recording in the studio. Tube active direct boxes and solid-state active direct boxes are both designed for studio use. Any instrument that lacks an internal power source is better suited for an Active DI box. Some good examples are acoustic instruments with piezo pickups, old keyboards like the Fender Rhodes and Wurlitzer EPs, and some classic basses.

For instruments like acoustic-electric guitars and electric basses, active DIs work brilliantly if you’re looking for a tone with higher attack, tonal definition and slap. However, aggressive slapping on the bass may cause an Active DI to distort. Active DI boxes work well for classic basses in that they aid in adding beef to the sound.

Active DI boxes are great for FOH engineers. However, some of these are AC powered. Hence, having an AC power near the stage setup is mandatory. Moreover, if Active DI boxes are plugged into a wall or a power source nearby, there lies the problem of ground loops.

While this problem can be managed with the use of a simple ground lift switch, you may have to keep switching between loud noise and less noise. Hence, a DI that uses phantom power works best for FOH engineers.

If the instrument in use has a built in preamp powered by a battery, then it may be more prudent to use a Passive DI. Passive DI boxes with high quality transformers are less expensive and won’t require batteries or an AC line or take up a phantom powered unit in the console.

RADIAL PRODI: A high quality Passive DI box

(Passive DI Box) Radial ProDI 1-channel Passive Instrument Direct Box

The PRODI is a passive mono direct box that is perfect for use with bass, acoustic guitars, synthesizers and electric pianos. The Radial PRODI is a full range Passive DI box that does not require batteries or any power supply.

All it takes for the Radial PRODI to cancel unwanted noise is a custom isolation transformer. It provides exceptional signal handling without saturation. It delivers extremely low phase distortion and eliminates hum/noise inducing ground loops by providing 100% isolation.

Additionally, there are isolated XLR connectors and a military grade PC board with a full surface ground plane to reduce any susceptibility to RF noise. Because of this and many more features, the signal retains excellent clarity and definition.

The plug and play feature in any audio device is a bonus in a studio/live setting, and PRODI is designed for plug and play. You just need to connect the instrument to the 1/4” inputs to your amplifier/mixer and the XLR output to the mixing console.

Overall, Radial PRODI works as well with acoustic instruments as it does with electric ones. It helps the natural tone of acoustic instruments come through and eliminates unfavorable ground loops while ensuring solid dynamics and a rich sound.

Radial J48: A high quality Active DI box

(Active DI Box Radial) J48 Stereo 2-channel Active Instrument Direct Box

The Radial J48 is an active DI designed to work with a 48V phantom power. Since there is limited current supply available with the phantom power, the J48 works best in this situation while still maintaining the pure and natural sound of the instrument.

High headroom without compromising the sound quality is one of the most important features of the Radial J48. Another product’s highlight is the switch mode supply. This sets up the internal rails to allow an input signal of up to 10V without any distortion whatsoever.

It is equipped with capacitors that provide sufficient current storage to ensure clean and unobstructed power for the signal. It possesses certain technical characteristics that significantly lower harmonic distortion.

The 80Hz HPF reduces low-end rumble and balances acoustic resonance. By doing so, the dynamic handling of the J48 is increased by 3dB or twice that of the power handling. This feature reduces mud and helps to increase the headroom simultaneously.

The input panel of the J48 has the usual 1/4″ input and thru put connections. The Merge function converts the thru put connection into a second input thereby summing stereo sources to mono such as stereo keyboards or CD players.

Overall, the J48 has several functions aimed at improving functionality and creativity. The J48 is capable of hitting up to 9 Volts without choking. High power consuming LEDs are turned off when the J48 is in use in order to increase the horsepower further.

Related Questions – DI BOX FAQ

Does a DI box reduce noise?

No, DI boxes typically do not help in reducing the external noise. The DI box functions to reduce the impedance by converting an unbalanced signal from the source (line level) into a balanced signal (mic level). During live gigs with big PA systems, a DI box helps eliminate interference over the long distance by balancing the signal.

Does a DI box boost signal?

The DI box does not help in boosting low-level signals. The DI box works in decreasing the impedance of the high (line) level signal coming from the source (unbalanced) to a low (mic) level signal (balanced) which goes into a sound desk microphone input.

How do I connect my DI box to my amp?

Connect the female end of the cable to the XLR output on the amplifier and the male end to the XLR input on the mixing console. In case of noise or disturbance, connect the XLR to an XLR- TRS pin and plug it in the 1/4″ line level on the mixing console. This results in a clearer sound because the microphone preamp is bypassed.

Can you play an electric guitar through a PA system?

It won’t be the best sound quality but it can work as long as the right preamps are built in. In this way, weak signals can be amplified to strong ones. However, the best option for guitarists is to go through an amplifier.

Can you use a DI box backwards?

DI boxes help in reducing the impedance of a high-level signal (line) and convert it into a low-level signal (mic). If a DI box were to work backwards, it may adversely affect the sound quality because the transformer in the Passive DI box would be operating at line level instead of mic level. Active DI boxes cannot function backwards.

Summary

The conception of DI boxes dates back to the 1960s in studios such as Motown and United Sound Systems. As a musician or audio engineer, you are better off understanding the features and functions of both types of DI boxes. To that end, we hope this article has served as a helping hand to understand their inner workings.

Featured Image by Ashley Pomeroy, CC BY-SA 3.0, via Wikimedia Commons 

We will be happy to hear your thoughts

Leave a reply