Choosing The Perfect DI Box

This is a continuation of yesterday’s introduction to DI boxes. If you haven’t caught part I, you can check it out right here!

So, now that we know a thing or two about DI boxes, what does that exactly mean for you? Which one is better? Do you need an expensive unit for your situation or would something simple and affordable be the best choice? How about active or passive? Well, before we answer all that and more, let’s start with the most important factor in determining what type of DI box best fits your needs. Much like preamps, pickups, effects or pretty much anything gear related that makes sound, when it comes to choosing a DI box, there are no hard rules – think of them more like suggestions or guidelines that can help guide you towards what you’re looking for.

Just like certain combinations of microphone and preamp offer different tonal qualities – not good or bad, just different – the same goes for DI boxes. But as far as the general consensus goes, a passive DI tends to give a rounder, thicker tone while active DIs offer more kick in the high-frequency area – very much like the tonal differences between tube and a solid-state preamps. But be aware that even among two passive or active units, small differences may be found, some of which you might not want so it’s always a good idea to check out reviews or forums to get a sense of what a specific model sounds like. Remember, here, we are only talking about generalities of DI units. Let’s check out some important ones.


Going Active

In general, passive DI boxes are recommended for active signal sources (such any instrument equipped with active pickups) while active DIs tend to be preferred for passive signal sources. But like most anything else, there are a few exceptions to the rule. Some active sources can work just as well with active DIs such as those designed to with higher voltage handling features. There are also DI boxes that allow users to operate them as either active or passive which comes in handy to have around in a studio setting where different instruments are always in rotation.

And speaking of the studio setting, if you plan on doing some direct recording you’ll most likely want the sound of an active DI. Basically any instrument that doesn’t have any form of internal power (e.g.: those with active pickups) should work well with an active DI box. Some examples would be acoustic instruments with piezo electric pickups, classis basses and old keyboards. Taking into specific account acoustic-electric guitars and electric basses, an active DI box can add some commonly sought after high-frequency sparkle which is perfect for adding some attack to aid in tonal definition or for slapping styles of bass. On the other hand, the dramatic transients produced by aggressive rhythm guitar playing and “slapping” and “popping” on bass can cause an active DI unit to distort in not son pleasant ways.

A good tip for those using a high-output (also known as “hot”) acoustic-electric guitar or bass, you should look for a DI box with the ability to handle high voltages such as the Radial J48. If you’re playing a classic, standard-output bass and feeling like it needs a bit more of a kick then an active DI is the answer. Today, there are active direct boxes that are specifically made with bass in mind such as the A Designs REDDI, or the Avalon U5. Both of these work just as well with guitars, synths and keyboards too in case you’re wondering. There are also some units that act like a combination of a DI and preamp designed specifically for electric and acoustic guitars, as well as other specific instruments.

Some advice for bands setting up a PA system for gigs and aspiring live sound engineers: Certain active DIs are AC powered. Not a problem in the studio but it might make them a little complicated for live performance use since you’ll have to make sure there’s AC power near the stage setup. Also, plugging an active DI into a nearby wall or power source can cause ground loops. Most, if not all, active DIs have a ground lift switch to solve that problem; however, you might find yourself switching between loud noise and less noise. From a live sound engineer’s point of view, a DI that uses phantom power might be a better choice.  


Passive Aggression

If you’re using an instrument with a built-in battery-powered preamp, such as an acoustic-electric guitar or bass, a passive DI will do the trick. Also, modern electronic keyboards and CD players are quite capable of producing output levels sufficient to overdrive an active DI. As mentioned earlier, there are active DIs that can handle the high voltage requirements of these instruments and devices; however, a passive DI with a quality transformer is less expensive and won’t require batteries or an AC line, or take up a phantom-powered input in your console. For noise-related problem solving in live stage environments when there’s little time to troubleshoot noise from ground loops, etc., it’s good to have a few passive DIs on hand – just in case.


Further Tips and Things to Think About

As with preamps, look for an DI box – either active or passive – with high-quality transformers and a wide dynamic range. In live performance a wide-bandwidth DI will preserve the harmonic content of your instrument that lives above 20kHz. Along with enhanced sound quality, there is acoustic information in the upper frequency range that is a component of your instrument’s attack. And, as mentioned earlier, poorly designed transformers can wreak havoc on the upper frequencies. The benefit of quality transformers and wide bandwidth is better definition and spatial localization which in turn allows your instrument to cut out its own space in the mix.

As any experienced live sound engineer will tell you, the fastest and easiest way to eliminate ground loop hum is to put a transformer in-between the offending units. Passive DIs such as the Whirlwind IMP-2 are quite affordable and do the job more than adequately.

A common use of the DI for an impressive sound in the studio is to combine a miked signal and a DI signal into two channels and blend them. The trick is to use phase reverse on the DI. If your DI or console does not have a phase reversal switch, you can wire an XLR cable to be out of phase. (Just swap pins 2 and 3 on one end of the cable and put some red tape on it so you don’t use it elsewhere.) If you’re recording to a DAW, just invert one of the channels (you can find this command in the Audio menu of most DAW software).

If you’re using an unbalanced line-out from your console to feed a house speaker system and experience loud 60-cycle hum, put a passive DI with isolated outputs (floating transformer) and a ground-lift switch such as the Pro Co DB-1 in between your console’s unbalanced output cable and the house system’s input cable. If you still hear noise, flipping the ground-lift switch should solve the problem.

And finally, if you’re using a passive DI to send an output from an electric guitar amplifier to a console, do not sit the DI on top of your amp! The magnetic fields produced by the amp’s power transformers will defeat the DI’ s electronic isolation properties by interfering with its transformer. Noise and possible phase and frequency shift will be the result.

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