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Mixing 101 Part 1: Inputs, Gain, and EQ Basics

For the uninitiated, there are few things in the realm of sound reinforcement more intimidating than the dreaded mixing console. I mean, just LOOK AT IT: all those knobs and buttons and sliders and faders and jacks and…*hysterical breathing*… You get my point. And whether you’re the slickest mofo in the recording studio or you’ve only recently professed an interest in the more technical side of music and audio, we’ve all been at that overwhelmed “where do I even start” point when it comes to mixing live sound.

I know that for me, growing up around performing and recording musicians and sound techs and being a musician myself, instruments, my tools for wielding RAWK, made sense to me. But all that PA equipment? I used to file that under “Magic” and just never engaged it much. Not that I wasn’t interested, I was just intimidated. But over the last few years as I’ve transformed from just a musician to a musician-slash-tech nerd, I’ve come to understand this about mixers: they aren’t nearly as complicated as they look.

If you’ve found yourself wanting to learn more about mixers and what they’re for and how they work but you haven’t had the faintest idea how to begin wrapping your brain around it, this blog was written with you in mind. If you’re a well-seasoned sound engineering professional looking to pursue the murky depths of the more nuanced parts of audio mixing, stand by for later blogs. We mere mortals must take it one step at a time. Step one!

Mixing 101: Assuming You Know Jack Squat

This is probably one of the best ways mixers (at their most basic level) were ever explained to me: any control on a mixer is essentially addressing one of 3 things about an audio signal…

1. Where From?

2. Where To?

3. How Much?

Or, in order of operation, 1) Getting signal in, 2) Messing with signal until it sounds good, 3) Sending signal out. Truthfully, a mixer is just a collection of multiple sound sources all cobbled together in a way that sounds good and is coherent and is then routed back out to one or more destinations. Bam. Mic drop. I could end this article on that note alone. But that’d be boring :)

To best understand how a mixer works, it’s necessary to have a solid understanding of the signal path when reinforcing live or recorded sound in general. Beginning with the signal source itself, you gotta get that sound into the mixer, then make it useable for the mixer, and finally making it listenable to the audience using the mixing controls and outputs. These are the basic steps to any sound reinforcement project.

For the purposes of this blog (Part 1 of likely several parts), I’m just going to focus on the first two operations of basic mixing: getting sound IN (where from) and setting sound UP for the mixer to use (how much). This is because A) it’s easier to understand a mixer if you take it one bite at a time and B) I have a tendency to rabbit-trail and go a little too deep into the murkiness of things and confuse myself and others. Yay.

Step 1: Getting Sound INTO the Mixer

The signal flow of a live music PA system can be expressed even this simply… Something creates a sound and that sound is converted from a physical sound pressure phenomenon (acoustic energy) into an electrical signal via transduction (again, magic). The transducer, be it a microphone or a guitar pickup or whatever, sends the newly converted signal down a length of cable (sometimes through other devices, like a D.I. or a preamp, which we won’t get into this time) and is fed into the mixer according to the corresponding inputs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Most mixers come equipped with at least two kinds of inputs: XLR inputs for microphones and other balanced signals, and ¼” inputs for instruments and/or line-level signals.

 

 

 

 

 

 

 

Again, for the sake of simplicity, if you don’t know what line level means, don’t worry. We’re just covering the most general topics at this time.

It is fair to say that not all output signals are created equal. In professional audio, we have a handful of categories we use to distinguish different output level types, so you’ll hear things like “line level”, “instrument level”, “microphone level”, and sometimes “speaker level”. For the purposes of this blog, keep in mind that everything from the keyboard’s signal to the acoustic guitar to the vocalist produces a different type of output level and sometime require additional devices and equipment to render them useful to the mixing console (even prior to gain staging and EQ).

Once you’ve got your sound sources fed into the mixer inputs, things start gettin’ real. For example, let’s say we’ve got a four piece band: a drummer, a bass player, a lead vocalist, and a tuba. Beginning with your tuba, hooked up to Channel One, the magical journey down the control strip starts.

 

Let’s say we have the tuba mic’d up in such a way that it is running direct into the XLR input on Channel One, and we’ll descend from there. After your input jacks, the next most obvious control on the console in the Gain/Trim control (we’ll skip Inserts and things like that for now). This is the first instance of a typical mixer’s “How Much”…

Step 2: Screwin’ Around with the Signal Until it Sounds Good

Gain staging, like any other part of the mixing process, is often misunderstood right from the get-go. Even veteran sound engineers sometimes get the concept of dialing in Gain levels a little sideways, much less the average rookie sound reinforce. Having spent the bulk of my live mixing experience in churches and small coffee shop-style venues, the most common audio misconception I come across is a simple, but crucial, misunderstanding about the nature of Gain control.

What is Gain and what’s it for anyhow? I’ll tell you up front first: Gain is not the same volume. It is similar in that you are increasing the overall level of an audio signal, but there is a big difference in purpose. Unlike Volume, which is a function of loudness and output level, Gain is a function of total input level. Loudness is what your volume faders are for.

 

 

 

 

 

 

 

 

 

 

Harking back to my weird little rabbit-trail above about how “not all signals are created equal”, remember that every sound source produces a different signal strength. Being that a microphone is going to produce a different signal type than say, electric guitar or an effects processor, we need to understand that a mixing console needs to see a certain signal level in order to work with it. This means that all these different input signals need to be adjusted according to their original levels and brought up to the level that the mixer can “see” them (i.e. line level). Phew! Here’s a new drinking game: take a drink whenever you read the word “level”.

How do we bring input levels (drink) up to snuff for our mixer to use? That, my friends, is Gain’s purpose in life. Basically, when you turn the Gain knob up, you are increasing how much of that signal source is being fed into the mixer. An analogy that isn’t 100% accurate, but helps my brain at least, is to think of Gain is terms of water pouring into a sink.

You’ve got water coming in from the pipe (your signal source) that feeds into a faucet (the gain knob) which controls the amount of water pouring into the sink (the mixer). But don’t follow that analogy too far, otherwise we start getting into overflow traps and drain stops and septic tanks and we all know that the only septic tank analogy in pro audio is the drummer’s girlfriend.

…that one’s gonna get me some angry emails…

For this blog, I’m choosing only to cover what Gain is and why we’ve got it on our mixers. The concept of Gain staging itself deserves its own series of blog posts and honestly, it’s all I can do not to geek out and start ranting about deeper, creepier parts of it…but for the sake of my own attention span (and yours), let’s move on down the line.

So we’ve got your tuba, your vocalist, your drum mics, and the bass player’s channels all gained up in the best possible way for your mixer to utilize. That was your first “how much” function in the mixer, meant to establish your overall input level (drink). The next “how much” gets a little more…nitpicky.

 

If Gain and Volume are concerned with the quantity of your sound levels (drink), Equalization (commonly shortened to EQ) is basically how you dial in the quality of each sound before you start sending it places to be listened to and/or recorded. Any given mixer can be as simple a single tone knob (turn clockwise, it boost highs and cuts lows, and visa-versa) to a 33+ Graphic EQ with adjustable sweeps and all that fancy-pantsy stuff. Generally, the larger the mixing console, the more precise you can get with the EQ’s control.

I won’t dive into the dark complexities of how human hearing works except that human hearing ain’t a straight-forward thing and a lot of it is about perception of sound. There’s some science and mathematical theory as to what frequencies sound good to us when, and how and why, but for now you can think of it like this: having control over these frequencies means having control over the perceived “goodness” of the sound. In other words, EQ is how to make stuff sound good/better by boosting or cutting frequencies.

Let’s imagine we’ve got a pretty simple, small-ish analog mixer with a 3-band EQ. You’ve got 3 knobs per input channel: one for low frequencies, one for mid frequencies, and one for highs.

 

 

 

 

 

 

 

 

 

 

 

These controls represent three chunks sliced out of the human hearing spectrum often measured in Hertz or kilohertz. For each sound source to be heard “best” when mixed together, some of these frequencies need to be cut or boosted. Yes, there are plenty of science-y guidelines for “what sounds good for a [insert instrument/source here], but this is the part of mixing that I would consider more art than science. You can teach a sound engineer to memorize frequency bands and formulas, but you can’t always teach good hearing ;)

However.

Allow me to share with you the not-so-patented Bigfoot Golden Rule of EQ-ing: always cut before boosting. For example! Imagine your tuba is coming through your main mix plenty loud but it sounds a bit muffled and thumpy. Not very clear or articulate. When using the 3-band EQ on your tuba’s channel, first cut the lows and maybe some of the mids and then subsequently boost the highs to achieve a clearer tone. Or, let’s say the opposite situation is true and the tuba is coming through brittle, tinny, and just downright unpleasant. Roll off some o’ dat treble, and then reinforce the bass and mids to round out the audio image and give the tuba some blood and guys. Again, it’s kind of like painting: there are general rules and guidelines, but ultimately…you’re the sound engineer and your ear determines what is needed. Yes, I’m giving you permission to be drunk with power (if you’re not already drunk from our “level” drinking game). AHAHA!

 So that’s the gist of getting started with a live mixing project. Consider this blog a cursory look at what a mixer is and what it does. There is still quite a lot to talk about (we haven’t even gotten to outputs, inserts, auxiliaries, sends/returns, blah blah), but for the sake of simplicity, I’ll keep the focus on “Where From” and the basics on “How Much”. Stay tuned for the Mixing 101: Part 2!

Stay excellent and have a good week! 


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