Most home studios contain an arsenal of carefully chosen gear. From synths and groove boxes to
guitars and drums, the tools in your studio need to be connected properly to work. But for some types
of gear, making the right connection means you’ll need an extra piece of equipment—a DI box.
A DI box is a utility tool that corrects signal level and impedance to make audio gear compatible.
The term DI stands for Direct Injection. The first DIs were built to allow engineers to plug electric
basses and guitars directly into the studio mixing console instead of mic'ing an amplifier.
DIs are commonly used for those instruments as well as synthesizers, drum machines and other gear with ¼” outputs.
Using a DI you can plug these sources into an XLR microphone preamp input like those you might find on a
mixer or audio interface.
DI boxes contain a transformer that electrically isolates the source from its destination. That’s why DI boxes are frequently used to address signal issues like ground loops.
Not all the audio sources in your home studio carry the same type of signal. There are different connector types, different signal levels and different impedances. Your signal fidelity can get worse if some of these qualities are mismatched. One of the most common examples is when you connect ¼” instruments such as electric guitar and bass to a mic preamp or audio interface.
The guitar signal coming from the pickups is a high impedance, instrument level signal. The mic preamp is expecting to see a low impedance, mic level signal. Even if you converted the ¼” and XLR connectors with an adapter, the signal and impedance mismatch would cause poor sound through the preamp. To fix it you’ll need a DI box to manage the signal level and impedance conversion so that the mic preamp works properly.
The same goes for most types of gear with ¼” outputs like synths, drum machines and samplers. Hot tip: Some hardware has ¼” outputs that are strong enough to be plugged directly into a mixer at line level. Gear like this doesn’t strictly need a DI as long as the destination has line level inputs. However, you may find using a DI box to pass the signal through the mic preamp sounds more pleasing.
There are two main types of DI boxes—active and passive. Passive DI boxes don’t require a power supply to run. The transformer inside performs the electrical operations that convert the signal.
DIs work well for most applications and are sometimes more affordable than their active counterparts. They can also be used with extremely strong signals since there’s no electrical circuitry to overload. Active DIs use phantom power to run an electrical buffer circuit that makes the signal stronger and helps it maintain fidelity. These are a good choice for low level instruments and long cable runs.
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