Welcome back to part two in our series on the basics of sound reinforcement. If you missed part one on setting up your PA, it’s worth going back and taking a gander. I talk about what gear you need and how to set it up for different spaces and situations. In this post I’m going to talk about what to do with your mixer once you are set up and ready to make some noise.
Most mixers have predominantly XLR inputs which are grounded. Some have 1/4″ line level inputs and then some have 1/4″ TRS inputs which are grounded (two stripes on the plug). It’s very important to have everything coming in to your mixer grounded. What does that mean? If you think about it like electrical plugs, some have 2 prongs and some have 3. XLR mic cables are like 3 prong electrical cords. They have a positive, negative, and a ground. It’s important to have grounded lines all going into your mixer because this is the #1 cause for noise & buzzing in your mix. Microphones are easy. They have XLR mic connectors and you connect them to an XLR mic input. In the same way, guitar amps are most often also mic’d. Sometimes bass amps get mic’d or many come with a built in XLR output which also works great.
It gets tricky with instruments like electric-acoustic guitars. Most electric-acoustics come with a 1/4″ instrument output. Sometimes you go in direct and it’s okay, but often times you’ll put a tuner in between and maybe that tuner plugs in to an electrical outlet…buzzzzzz! The preferred method for electric-acoustics is to go from your guitar or tuner into a DI box which grounds the signal and has an XLR output to safely go into your mixer. This same method is used for things like keyboards and synths that can have a variety of outputs depending on the brand & model. MP3 players or computers can also be connected through a DI box unless you are fortunate enough to have stereo RCA inputs for a house music mix. A lot of standard analog Mackie’s have that option, but I’m seeing it less and less on newer boards, especially digital ones.
Back to microphones. Another thing to note is that some mics require phantom power. I’ll spend more time on mic selection in a future post because it is it’s own art, but for this discussion there are two basic types of microphones you’ll be using, dynamic and condensers. Most dynamic mics do not require any extra power, but condensers tend to be more sensitive and need more juice. Not all mixers even come with phantom power built in. Some only offer it on certain channels, some have it on all. Higher end mixers have it available on every channel, but it can be switched on and off on a channel by channel basis. One of the most common reasons for a mic not working is that it requires phantom power and you either have it on a channel that doesn’t have it, or you forgot to switch it on. (Happens all the time!)
Gain & Unity
This is THE most misunderstood concept with folks who are unfamiliar with mixers. People get all excited about the faders which are so cool, but they ignore the gain controls! Faders are for mixing. This important tool is what’s usually located near the top of the board and is labeled as gain or trim. This is where you establish the base volume for your input. You want to start every channel with the fader at what is known as unity. The best way I can describe unity is the ideal volume for that particular instrument or channel. On many mixers it’s marked as a “U” on the decibel indicator. Some boards have a numbered scale instead of U, so you want to see if there is a zero with more room above if like +15db. If that’s the case, 0db is unity. There are other mixers out there that have 0 at the very top. In that case -6db or -12db are better for setting that as your unity so that there is room to go up or down. Once unity is established, then you can start to adjust your mix by bringing some channels down or up. If your gain is too weak the sound is faint and puny. If it’s too strong then it clips and distorts. When you are getting started before you do anything else like EQ, you want to establish your channels at unity so that they have the best baseline sound quality.
The outputs can go from as simple as a mono send to a powered speaker to multiple monitor mixes, to multiple house speaker configurations with their own mixes and EQ. For simplicity’s sake (since you’re probably not reading this if you need to set up for a production of Jesus Christ Superstar) we’ll do a main mix and a monitor mix. You want to set up or “tune” your speakers with the mix at unity. That may mean that you don’t have your amp or powered speakers very high for a small room. I’ve seen people have the main out fader way down because their speakers are cranked. This results in a bunch of hiss coming out of the speakers and a weak mix coming out from the board. It’s just not ideal. In the same way, if you crank your output control and don’t have your amp or speakers turned up loud enough you get a lot of distortion which doesn’t sound very good either. If you’d like a separate mix for your monitors, that’s where you use a Bus or Aux send. This allows you to have only vocals and maybe a rhythm instrument in a speaker near you without having everything coming though. In more complicated set ups you can have an Aux send for your sub so that only your bass and kick drum go to that speaker. It can get more complicated especially if you also have to send channels to an effects processor, but you get the idea. Set your channels, set your main send and then adjust your amp or powered speakers from there, that’s the main point here.
Basic rule of thumb on EQ is to start everything at unity or zero and then trim as needed. Many simple mixers have just treble & bass. If you are fortunate enough to have parametric EQ or a sweepable mid you can really go after some frequencies that are causing feedback or just don’t sound very pleasant, but for the most part all you want to do with EQ is trim out harshness in the treble range or boominess in the low end. If your mixer has a high pass filter, often seen as a button, that will cut out the unnecessary muddy low end on most of your channels and clean up your mix. There are some fantastic techniques on EQ that you can do with more sophisticated mixers, especially if they have a nice interface or an iPad app. If you want to learn more, there’s a terrific tutorial for home recording that also applies to live mixing if your board allows over at www.therecordingrevolution.com.
You’re finally ready to mix! All you really want to do here is keep what needs to cut through the most at the unity level and then dial the other channels back as needed. Ideally, you have someone mixing live during a worship service, but if not, make sure that things like vocals aren’t getting drowned out by the band. If there’s a lot of natural volume from an instrument or amp you don’t need as much of it in your main mix. Leave room to boost an electric guitar or featured instrument. This is what the faders are all about. If you have instruments that aren’t always playing or on, go ahead and cut down noise by muting them or dropping their level all the way until they are back in. If you experience a lot of feedback, then you may need to cut the level of everything down. You also may need to adjust the position of your main speakers or monitors. Good placement of your speakers and EQ will help reduce those problems.