Do I Need a DI Box?

This blog post is first of a three-part series that covers DI boxes, getting the best mix in a live environment, and finally reamp boxes. Yup, all three are actually highly inter-related.

What’s a concert stage wired like?

Before we get into DI, let’s think for a moment about what the wiring on a stage looks like. Professional PA mixing consoles are designed to take in XLR microphone level inputs that connect to onboard microphone preamps. Consumer level mixers often have a limited number of mic inputs, and lots of 1/4” line-level inputs. This is because the XLR connectors and mic preamps are expensive where as 1/4” jacks with no preamp allows the manufacturer to advertise many more channels for a cheaper price. Professional quality mixers generally don’t play this trick, every advertised input has an XLR mic preamp.

The reason why this is important to note is because at home or rehearsal you may use one of these consumer level mixers and are sending line-level signals from a keyboard, an e-drum kit or even your guitar modelling amp into those line-level mixer inputs because that’s what they’re there for.

Consumer level mixers provide lots of line-level inputs. These are the 1/4″ jacks to the right of the XLR jacks present on Channels 1-4.
Pro mixing consoles have a mic preamp on every channel input. You can tell because every fader has idential knobs (the channel strip) above it.
On this Mackie 1604 all the channel inputs are on the back.

However, when you get to a venue like a festival with many bands playing, the sound crew can get grumpy if you try to send them line-level. They want everything coming from the stage at mic-level. Why would they want this? Isn’t line-level a stronger signal and better than mic level? Maybe in a studio with fixed wiring, but not at a dynamic environment like a live venue.

The sound guy has to deal with multiple bands, all with different numbers of instruments and microphones being used. Sound checks and change overs need to happen fast and with so many channels, trying to reconfigure the preamp gain for each channel depending on whether it is mic level or line level will take too much time. If every channel input on the mixer is always fed mic level, then everything gets a lot simpler and sound checks go much faster. If a particular channel cuts out, they can quickly switch to another channel.

If you want be professional, be prepared to send mic-level signals, regardless of what kind of instrument you have.

A mic preamp works best when it’s connected to a mic signal. That implies a specific output impedance from whatever is plugged into it, as well as a certain signal level. Professional sound engineers particularly like simplicity and reliability. Mic signals are always balanced, which means they reject common noise. Any noise sources (from lighting, radio interference, etc.) hit both wires in the mic cable pretty much the same way and so the interference is “common” to both, and is effectively eliminated by the mic preamp. Balanced signals only use the ground connection for shielding, so lifting (disconnecting) the ground at only one end will break any ground loops while keeping the benefits of shielding intact.

Mic signals can also be run for very long distances (100 feet) without significant degradation if the cabling is good quality. In summary, despite line-level potentially being a higher quality singal, for simplicity it makes sense for sound engineers to treat (or convert) everything to a mic signal at a venue. This greatly simplifies how the sound system is connected and problems are easier to track down.

So do you need a DI box?

Maybe. In a nutshell, DI boxes are most commonly used to convert whatever you have to something that looks very much like a mic signal. So, if you always keep your amp right next to you and always mic it, then no. You’ve got a short instrument cable from your guitar to your amp, and then you’ve got a mic on the cabinet. You’re sending a mic signal to the mixing console so you’re good, no need for a DI here. However, you may want to stick around for the rest of this article to see what other scenarios you might run into where a DI is going to be needed.

What if you are further than 20 feet away from the amp? What if you play a bass? What if you use digital modelling processors or amps?

What if you’ve noticed (or been told) that your band sounds like a wall of mud on stage. Oh crap! Can a DI fix that?

In Part 2 of this 3-part series, we’ll talk about how to get a better sounding mix in a live environment, and how a DI can play a role in achieving that goal.