So, you’ve got an audio interface and you can record an electric guitar (or any instrument level signal) to it. It’s a great solution that handles many recording situations, yet there are still producers who insist that direct boxes are indispensable units for recording.
If you’re new to the idea of direct boxes, here’s a crash course. A direct box, or direct input (DI) box, takes the unbalanced signal of an electric instrument and converts it to a balanced signal with the proper impedance for a mixing board. In the days before audio interfaces, they were required for recording direct to tape, since mixing boards don’t accept instrument level signal.
Now that audio interfaces are the main avenue for signals going to “tape,” there are fewer uses for direct boxes. But, some remain.
First, there is the issue of interference. Unbalanced signals running through a cable from a guitar are incredibly susceptible to electromagnetic interference. As the cable gets longer, interference increases to create unwanted hums and buzzing noises in the signal. It’s recommended that instrument cables are no longer than 20 feet.
The direct box is a great way around that problem. Direct boxes convert unbalanced signals to balanced, at which point the signal can travel as far as it needs to, interference free. In this case, the direct box is perfect for extending the reach of an instrument without losing signal quality. You can shorten your unbalanced cables and improve your instrument signal with a direct box.
Another, more obvious use for direct boxes is for monitoring. Recording instruments direct to disk is fine, but it lacks the feeling of playing live. A guitarist who relies on hearing the sound of their amp can still record direct and through their amp, thanks to direct input. The sound leaving the direct box can be routed into your DAW, and into the amp, making everybody happy.
Of course, when it comes to buying a direct box, there are options. Check out this buying guide from Bestcovery, which covers some of the best direct boxes on the market.
Here’s a taste:
Certain DI boxes can even help to achieve a warm tone, for example, or to roll-off unwanted frequencies in a natural and sonically pleasing way. The very best passive DI boxes can accomplish this effect and require no power source to operate. Active DI boxes, on the other hand, do require power but allow for greater headroom and finer detail in the sound being recorded. Most engineers have a variety of DIs on hand, so use the following list as an educated jumping-off point for your personal studio collection.