Our DI box recommendations

We have three main products we’d like to highlight here for high-performance DI boxes, so before we get too technical, here are our picks:

What is a DI box?

Traditionally, instruments like electric guitars, organs, keyboards, and bass guitars were recorded by placing a microphone in front of an amplifier’s speakers. In the 1960s, however, engineers started wanting to take a direct signal into the mixing desks for a more accurate sound. They called this “Direct Inject”, hence the term DI box.

There was one key problem though: the output volume of these instruments is much higher than that of a microphone, which would create significant distortion in the recording.

Enter DI boxes. These handy devices were made to solve the disparity in volume between these two signals, allowing guitarists and keyboard players to record directly into the console. Guitarists like U2’s The Edge and Pink Floyd’s David Gilmour were fans of doing this.

Engineers found themselves with more tonal control through the console EQ and a much easier recording setup, as well as the possibility of clipping the preamp to add some distortion to the sound.

DI box designs advanced further over the years, with extra features to solve problems such as “Thru” outputs, which allowed the instrument-level signal to carry on. This allowed musicians to take a DI of their instrument while sending the original signal to pedalboards and guitar amps.

“Thru” outputs also allowed for reamping, where studio engineers could use a reamp box, a reversed DI box that converted the balanced line level signal back to instrument level. They could then send the DI signal back out of the console to amps in order to refine, change, or add extra layers to guitar tones and get something that would fit the mix better or sounded bigger.

Ground lift switches helped prevent electrical interference, and these simple little boxes became key elements of studio recording.

These features also solved a lot of issues in live shows, ensuring a clean guitar signal, a backup DI in case of amp failure, or even the ability to merge multiple signals into a single mixer channel.

When to use a passive DI box

A passive DI box is best suited to high-output instruments like electric guitars, basses with active pickups, and keyboards.

These instruments produce a strong signal that doesn’t need additional boosting, making an active circuit unnecessary. Instead, passive DI boxes rely on a transformer to convert the unbalanced, high-impedance signal into a balanced, low-impedance one, reducing noise and interference over long cable runs.

Most passive DI boxes use a high-quality isolation transformer, often made from materials like mu-metal to minimise distortion and maintain signal clarity. Some models include extra features such as a pad switch to handle particularly hot signals, a ground lift to eliminate hum, and multiple outputs for signal splitting.

Passive DI boxes are ideal for live performances and studio setups where simplicity and reliability are key. They require no external power, making them convenient for quick stage changes and reducing potential power supply issues. If you’re using a keyboard or a bass with an onboard preamp, a passive DI box will preserve your tone without adding unnecessary colouration.

For a reliable passive DI box, we’d recommend the SubZero Passive DI Box.

When to use an active DI box

An active DI box is the best choice for low-output instruments like passive electric basses, acoustic guitars without a preamp, and vintage keyboards. Unlike passive models, active DIs include a built-in preamp to boost weak signals before they reach a mixer or audio interface, ensuring clarity and consistency.

These DI boxes require power, either from a battery or phantom power supplied by a mixing desk or audio interface. Many active models include features like gain controls, high-pass filters to remove unwanted low-end rumble, and polarity switches to help with phase alignment in multi-mic setups. Some also offer multiple outputs for splitting signals between amplifiers and PA systems.

An active DI is especially useful in recording and live sound applications where signal integrity is crucial. If you’re using a passive instrument with long cable runs, an active DI will maintain sound quality by preventing signal degradation. However, active DIs may not be ideal for high-output instruments like keyboards or active basses as their preamps can introduce unnecessary gain and potential distortion.

For a high-quality and industry-standard active DI box, we recommend the Radial J48, which has become a standard choice for professional studios.

What to look for in a DI box

Ground lift

The ground lift switch on a DI box helps eliminate unwanted hum and buzz caused by ground loops. A ground loop occurs when there are multiple paths to earth in an audio system, leading to electrical interference and noise.

Activating the ground lift disconnects the electrical ground connection between the input and output, breaking the loop while still allowing the audio signal to pass through. This is particularly useful in live and studio environments where different pieces of equipment are powered from separate sources. If you experience persistent hum, using the ground lift can often resolve the issue without affecting sound quality.

Pad

The pad switch on a DI box reduces the input signal level to prevent distortion from overly strong signals. This is useful when connecting high-output instruments like keyboards, drum machines, or active basses, which can otherwise overload the DI box and cause clipping.

Pads are typically available in fixed values, but some DI boxes offer variable pads for greater control. Engaging the pad ensures a clean, undistorted signal while preserving tone. If your signal sounds distorted even at normal levels, activating the pad can help maintain clarity without affecting overall sound quality.

Thru/bypass

The thru or bypass output on a DI box allows you to send an unaltered copy of your instrument’s signal to another destination, such as an amplifier, while the balanced output goes to a mixer or audio interface. This is especially useful for bassists and guitarists who need to hear their amp on stage while also sending a clean signal to the front-of-house or recording setup.

In studio and live settings, the thru output ensures you can capture both a direct and an amplified signal simultaneously. This provides flexibility for blending tones or re-amping later in the mixing process.

Multiple channels

A multi-channel DI box allows you to process multiple instrument signals within a single unit, reducing clutter and simplifying setup. This is particularly useful for stereo keyboards, electronic drum kits, and multi-instrument rigs, where each output needs to be balanced and noise-free.

In live sound, a multi-channel DI box streamlines stage connections, making it easier for sound engineers to manage multiple sources. In the studio, it helps when recording multiple direct signals simultaneously, ensuring consistency across tracks. Consolidating several DIs into one unit also saves space in racks and pedalboards while maintaining high-quality signal conversion.

Polarity reverse

The polarity reverse switch on a DI box flips the phase of the signal by 180 degrees. This is useful when combining multiple sound sources that may be out of phase, which can cause cancellations and a thin or weak sound.

In live and studio settings, polarity reversal helps when using multiple microphones on a single instrument, such as a bass DI and a mic on a bass amp. It can also resolve phase issues when integrating DI signals with amplified sources. If you notice a loss of low-end or an unnatural tone, engaging the polarity switch can restore clarity and balance.

FAQs

What is the purpose of a DI box?

The purpose of a DI box is to convert high-impedance, unbalanced signals into low-impedance, balanced signals. This helps reduce noise and interference while allowing instruments like electric guitars and keyboards to connect directly to mixing consoles or audio interfaces. DI boxes are essential for clean signal transmission in live and studio setups.

What is the disadvantage of using a DI box?

The disadvantage of using a DI box is that it can slightly alter the tone and dynamics of the signal. Passive DI boxes may cause signal loss, while active DI boxes require power, adding complexity. Additionally, using a DI box may introduce extra cables and connections, increasing setup time and potential failure points.

Do you need a DI box if you have an amp?

Having an amp does not necessarily eliminate the need for a DI box. If you want to send a clean, balanced signal to a mixer or recording device, a DI box may still be required. Many amps have built-in DI outputs, but if yours doesn’t, a DI box ensures proper impedance matching and noise reduction.

Final thoughts

While small and unassuming, DI boxes are essential tools for audio engineering. A reliable problem-solver in everything from bedroom studios to Abbey Road itself, and local pub stages all the way up to Glastonbury’s main stage, if there’s a guitar, keyboard, bass guitar, or drum machine around, a DI box may just give you all the extra flexibility you need.

They’re used for converting high-output instrument-level signals to quieter, balanced line-level for use with studio and live sound equipment; cutting electrical interference and noise from instrument signals; inverting polarity to prevent phase issues for a clearer signal; and allowing for reamps in the studio. In summary, DI boxes have a lot of functions!

And that’s what a DI box is and why you might just need one in your arsenal.

Looking for more tips to improve your sound? Here’s our guide to live sound mixing.

Looking to gig and not sure what you need to bring? Here’s our band equipment checklist.

Looking for an amp to use with your new DI box? Here are our favourite guitar amps on the market.