Among the dozens of gadgets we use as musicians…there are few tools more misunderstood than the direct box, aka DI box.
Virtually every stage rig will have them in some form or another…
And in the studio, virtually every audio interface has one built-in.
Yet how many of us can truly explain exactly what it is they do?
Worse still…when buying a direct box, how do you even begin sorting through all the potential options?
Well, if you want answers…that’s exactly what you’ll find in today’s post.
Let’s begin. First up, the basics…
Table of Contents:
- What Exactly is a Direct Box?
- Passive vs Active Direct Boxes
- Acoustic DI’s
- Stereo DI’s
- Multi-Channel DI’s
- How much to spend on YOUR direct box
What Exactly is a Direct Box?
At its core, the direct box has ONE fundamental purpose:
To convert a hi-z unbalanced instrument signal into a low-z balanced mic signal.
Now here’s how that helps you:
On-stage, it allows you to split an instrument signal…
Sending the balanced “output” to the mixer, and out the PA, and the unprocessed “thru” signal to your amp.
In the studio, it works similarly, except the balanced signal goes to your audio interface instead…
Which allows you to simultaneously record wet and dry versions of the same track.
In both cases, direct boxes have the added benefit of allowing you to send guitar signals over much longer distances without gathering noise.
Passive vs Active Direct Boxes
The real question on everyone’s mind is:
What’s the difference between active and passive DI’s?
The part that most people already understand is:
- Active DI’s require a power supply
- Passive DI’s don’t
Yet as I’m sure you suspect, there’s WAY more to the story than just that.
So let’s keep learning…shall we?
The Best Instruments for Active Direct Boxes
The first rule of thumb is:
Active DI’s work best with PASSIVE instruments, including:
- Electric Guitars
- Passive Basses
- Vintage Rhodes pianos
And that’s because…
Passive pickups output a weaker signal, and can therefore benefit from the amplification of active DI’s.
The Best Instruments for Passive Direct Boxes
As you might guess, the opposite rule of thumb applies here:
Passive DI’s work best with ACTIVE instruments, including:
- Active Basses
- Electronic Percussion
Since their on-board preamps output a hotter signal…
You don’t need the amplification that active DI’s provide.
But there’s more…
Passive DI’s typically have far more headroom than active DI’s, and can therefore handle hotter signals without overloading.
If and when they DO overload, passive DI’s produce a pleasant “saturating” distortion, while active DI’s have a much harsher sound, similar to digital clipping.
So that’s one scenario in which passive DI’s are ideal. The other scenario is live performaces…
Why Passive DI’s Work Better On-Stage
The problem with using active direct boxes on-stage is that each of their 3 possible power sources presents its own unique challenge:
- AC wall power – is a hassle to supply on-stage.
- Batteries – always die at the worst moment, and are expensive to replace.
- 48V phantom power – is normally not strong enough to provide adequate headroom.
Passive DI’s on the other hand, which DON’T use power, work better because they avoid each of these potential problems.
The other reason passive DI’s work better in live settings is…
The transformers they use in their circuitry are highly resistant ground loop hum.
By passing the audio signal through a magnetic field, transformers eliminate any direct electrical connection between the input and the output…
Thus blocking whatever ground loops may exist in the system.
Of course, some DI’s do this better than others, and up next, I’ll explain why…
Choosing a Good Passive DI
A common myth with passive direct boxes is that they’re all the same.
But the truth is:
The good ones really do sound far better than the cheap ones…
…and that’s mainly because of the transformer.
Under normal conditions, transformers are constantly exposed to multiple sources of interference which negatively impact the sound…
The most significant source being: the magnetic field from your amp.
To avoid this problem, good transformers use various kinds of shielding on the outer-casing to maintain isolation. And as it turns out, that shielding can be expensive…
Which is why, with passive direct boxes especially, you really do get what you pay for.
3 great options I recommend are:
While doing research online, I came across the following video on the Radial JDI, which includes tons of great information on passive DI’s in general. Check it out:
Choosing a Good Active DI
As I stated earlier, a big problem with most active DI’s is their inability to work well in live-settings.
So one sign of a good active DI, is its ability to overcome these challenges.
For example, with most active DI’s, the 48V phantom power has a tendency to introduce ground loops into the system…
But you can’t engage the ground lift switch without cutting off the phantom power.
To solve this problem, the Radial J48 converts 48V phantom power into AC, using a unique switching power supply that allows you to lift the ground without cutting off power.
Another common problem with 48V phantom power is: it restricts the DI’s internal working voltage to an extent that the available headroom is much less than typical passive DI’s.
The Radial J48 solves this problem with a unique power scheme that increases its internal rail voltage up to 9 volts…
Providing way more headroom than typical active DI’s.
Alternatively, here are some other top active DI’s I also recommend:
For the studio:
Again, here’s another great video by Radial with lots of great info on active DI’s:
Since acoustic guitars traditionally use passive piezo-electric pickups…
The standard rule of thumb suggests an active direct box, correct?
While that is true, these pickups have an even higher impedance than those found in active basses…
And therefore use special “acoustic DI’s” designed specifically for the instrument.
The biggest difference you’ll notice with these acoustic DI’s is…
They are far better at preserving high-frequency detail, which of course is essential to the sound of the acoustic guitar.
Among the top models on the market, here are the ones I recommend:
- LR Baggs Para DI – (Amazon/Thomann)
- LR Baggs Venue – (Amazon/Thomann)
- Fishman Aura Spectrum DI – (Amazon/B&H/Thomann)
- BBE Acoustimax – (Amazon/B&H/Thomann)
- Radial PZ-DI – (Amazon/B&H/Thomann)
On stereo outputs such as keyboards and electronic drums…
Stereo DI’s offer an easy solution to process BOTH channels through ONE device.
Another useful feature they sometimes have is a “MERGE” button…
Which mixes the STEREO channel down to a single MONO output.
The reason you would use this is:
At live events in larger venues, where fans are spread out over a wide area…
Stereo imaging can actually detract from the listening experience of those seated off to the sides.
So in this case, MONO is actually preferred, and the merge button makes it easy.
If you need a stereo DI for your rig, here are two great options I recommend:
As we all know, finding the perfect guitar tone takes time, right?
The problem is, musicians usually perform best on the first few takes…
And we often waste those takes experimenting with different tones and mic positions.
Recognizing this problem…
Engineers developed clever work-arounds that enabled them to tweak and re-record a track long after the take was finished, and the guitarist went home.
Then one day, a man named John Cuniberti designed a device known as the “re-amp“, which was designed specifically for this one purpose.
Here’s how it works:
You take the dry guitar track that was previously recorded, and send it out to the reamp.
The reamp takes the balanced line-level signal and converts it back into a guitar signal…which you then feed to the amp through a second guitar cable.
At this point, you can loop the pre-recorded track and take all the time you need to find that perfect sound.
Once you’ve got it, you just re-record it onto a new track, and you’re done! Simple, right?
If you’d like to try it, these are the top models I recommend:
- Radial ProRMP – (Amazon/B&H/Thomann)
- Radial Reamp JCR – (Amazon/B&H/Thomann)
- Radial X-Amp – (Amazon/B&H/Thomann)
- Little Labs Redeye – (Amazon/Thomann)
While they’re certainly overkill for the average home studio…
Multi-channel rackmounted DI’s are truly the best-of-the-best in the world of direct boxes…
…as they can offer enormous benefits to those who require them.
In pro studios and large live-rigs with complex routing…
They allow you to connect multiple guitars, to multiple amps, with multiple reamping loops.
And while you or I will likely never need one, it’s still nice to know they exist if the day comes when we do.
Not surprisingly, all the best DI’s in this category are made by Radial. Here are the ones I recommend:
- JD7 Injector – (Amazon)
- JD6 – (Amazon/B&H/Thomann)
- ProD8 – (Amazon/B&H/Thomann)
- JX44 Air Control – (Amazon/B&H/Thomann)
How much to spend on YOUR direct box
Now that we’ve covered the full-spectrum of DI options, you may have noticed that prices can range anywhere from $40 to over $1000.
The question is, how much should you spend on YOURS?
Well, as you may have also noticed, the guys over at Radial Engineering seem to have all the answers when it comes to direct boxes…
And it just so happens they have an answer this question as well.
According to their 5:1 Rule, they say that for every 5 dollars you spent on your instrument, you should invest 1 dollar on your direct box…
Meaning a 1000 dollar guitar, would warrant using a 200 dollar direct box.
Makes sense, right? Now we know.