How to Use an Audio Mixer (soundboard)

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Introduction: How to Use an Audio Mixer (soundboard)

In this instructable I am going to go through all the control features found on most mixers (mixing consoles, mixing desks, audio consoles, soundboards - they all refer to the same thing). I will start with the absolute basics:
What is a mixer?
A mixer, in its purest and simplest form, combines or meshes an array of inputs into a few controllable outputs (hence the name, MIXer). It is pretty much universal that mixers will have at least a volume control on the output. The vast majority will have volume or "level" controls on each input, or "channel." A great many still will have a variety of controls on each channel, from gains or trims to EQ and aux'es and buses and PFL's and more; don't worry though - I will go through each of these at least briefly.
When a new sound guy looks at a mixer for a large church, per se, he may feel overwhelmed by the oceans of knobs that may or may not be there. But here,I will explain what these knobs do, and you will actually find them to be overwhelmingly simple.

The first thing you need to know is that I will be dealing with moderate to large mixing desks and sound boards, with at least 10 channels (available inputs) or more. These are what you will see if you want to "run sound" for a church or venue or record music of bands, etc.

Step 1: Channels

The most important aspect of understanding mixers is understanding the channels. On almost all consoles, the channels are laid out in strips; the signal comes in physically through the back of the device, then passes through that channel's various controls from top to bottom, with the gain or trim at the top and the fader at the bottom. I will go through what each of these steps does in their own, well, steps.

Simply look at one of the black circle inputs (XLR's for microphones and snakes), then follow the column of knobs straight down. This is a channel strip.

Step 2: From the Top: Gain (Trim, Sens)

On any good size mixer there will be a knob at the very top (first one in the strip) labeled "Gain" or "Sens" or "Trim." These are all the same thing. Put simply, the gain knob sets the "input volume." Think of a water faucet: a full water "signal" comes in through the pipe (input cord), and the faucet itself (gain control) sort of limits the amount coming into the sink (mixer). Because of the way a sound signal is composed of several different sounds at different volumes mixed together, the gain will naturally eliminate some of the very quiet signals; unless it is set very high. It's like survival of the loudest, and the trim sets the bar on how present a signal must be to get into the mixer. For this reason, it is sometimes labeled as Sens., for sensitivity. A high gain will be more sensitive to quieter signals like soft overtones and even spit pops in microphones.

Using Gain
Many people make the mistake of mistaking gain for volume. This is wrong. Gain should be used just like any other control knob: to set the kind of sound you want and the quality, not volume. That is what faders are for. Additionally, any gain changes will also affect the sound in the monitors or other auxes, so be careful. If you don't know what those are, don't worry: I'll explain them later.
A common use for gain is to sort of even out or normalize the signal (calibration). This is done if you have a VU meter, which tells you how loud the output sound is. One would set your fader or output volume control to 0dB and alter the gain until the meter says the sound is at 0dB.

Step 3: EQ: Equalization

For those of you who are new to audio, equalization refers to the control (boosting, cutting) of certain frequencies to achieve a better sound or to eliminate feedback or unwanted noises. The EQ section of most mixers will be located right under the gain control, and can consist of anything from 1 to 13+ knobs or 3 to 33 sliders.

Tone Knob: One knob that, when turned clockwise boosts high frequencies and lowers low, and vice versa. Sometimes called contour, and usually found on very small mixers.

2-3 Band: Consists of bass and treble knobs or Low - Mid - High knobs. I don't think I need to explain these.

Semi - Parametric: Usually a 3 or 4 band (Low, Low-mid, High-mid, High) containing at least one sweep. A sweepable control is one that has a pair of knobs: one chooses a frequency to boost or cut, and the other sets the boost or cut. The Frequency knob is called a sweep.The mixer below has one sweepable band.

Fully Parametric: Every band has a sweep to go along with it.

Graphic: These contain sliders instead of knobs. Each slider has a set frequency and is moved to change the presence of that frequency. These are not commonly found on channels, but are often found on the total mix (right before the output goes out). I have seen graphic EQs with 3 sliders and some with 31+ sliders.

As you progress in size from small mixers to large, you will find the amount of control over the EQ of each channel increasing. Many of the large boards, like the Soundcraft MH series, have a 3rd control knob on their fully-parametric EQ bands: Q. Just as the sweep sets the "center" frequency to be boosted, the Q sets how wide the boost range is. If you think of an EQ band as a line with a hill or bump in it, the sweep sets where the bump is, the boost sets how high the bump is, and the Q sets how wide the bump is.
Many digital mixers allow you to actually have a graphic EQ on each channel. You would select the channel on the screen, and set its EQ. These can be troublesome, however, if you need to quickly cut a particular frequency in a live show before it causes feedback and time is crucial.
I have told you how to use EQ, but not how to be good at it. Many times it is best for newbies to leave the EQ on flat (no frequencies boosted or cut) if possible. Mastering use of EQ takes experience and research. Remember, however, that it can make an OK sound sound good, and a good sound great, but it cannot replace what should be in a bad sound.

Step 4: Auxiliary Outputs (Auxes)

Auxiliary outputs, or auxes, are incredibly useful tools. If you can, picture the signal coming into the mixer, going through the gain and the EQ, then hitting an aux knob. That knob controls how much of that signal from that channel gets sent into that aux out. On this board there are 4 aux outputs, thus 4 aux knobs on each channel. Each row of aux knobs controls the level of all the channels in its auxiliary output.
Example:
The most common use for auxes is stage monitors. Lets say that we have Bob on stage singing, and Joe playing guitar, and each has his own monitor. Lets also say we have Bob's voice plugged into channel 1, and the guitar in 2, and Bob's monitor in aux 1 and Joe's in aux 2. So, if Bob wanted more guitar in his monitor, we would go to channel 2 (where Joe's guitar is plugged in) and turn up the Aux 1 knob: this tells the board to put more of the signal in channel 2 into the device plugged into aux 1.

Two other common uses for auxes are reverbs (device that simulate reverberation effects) and subwoofers (loudspeakers designed to reproduce lower frequencies than normal speakers can play).

Step 5: Faders, PFL's and AFL's, Pre/Post Fader Auxes

The fader (present in small mixers as a level or volume knob) is used to set the volume of that channel's signal in the mix. It is the most basic component in any channel strip. Faders are essentially volume sliders, set in a logarithmic scale of dB (if you don't know what that means, ignore it). Faders are also used to set the volume of the buses, or subgroups, and the main mix or mixed mono, and VCA's if applicable. I'll get into those next step.

Auxes, you should know, are normally pre-fader by default. This means that changing the level of a channel on the fader will not affect the sound of that channel in the auxes. However, many medium-large boards have a button near the aux knobs that allows you to change them from pre-fader to post-fader or vice versa.
Example of pre/post fader auxes:
You are running sound for a rock band playing in a large room. Being the sound perfectionist you are, you have set up some subwoofers to help properly produce the low frequencies of the kick drum, floor tom, and bass guitar. The band also has monitors set up on stage. If you have the option, you will naturally want the monitors to be pre-fader, so that changes on the faders will not mess with the monitors. You will also, however, want the subwoofer auxes to be post-fader, so that the mains-subs balance remains the same after changing the fader settings. When you turn up the bass guitar fader, you want the bass signal in the monitors to stay the same, but the bass in the subwoofers needs to increase along with the bass in the main speakers.

Most medium-large size desks also have a headphones jack for the engineer to use headphones. You will also see a button near the fader on each channel labeled PFL. This stands for Pre-Fader Listen. This allows you to listen directly to the signal in any channel via the headphones, unaffected by the fader setting. You may also see a button near the aux masters (they set the total volume of the auxiliary outputs) labeled AFL. This stands for, you guessed it: After-Fader Listen. This allows you to hear the exact sound and volume coming out of the monitors or whatever else you have plugged into the auxes.

You should also realize that above the fader, just after the auxes, is a pan knob. This is simply used to "pan" the channel's signal to left or right. All the way to the left would put the signal only in the left signal, and vice versa, with the middle sending equal to both sides.

Step 6: Buses (subgroups), Main Mix, VCA's

Almost all decent sized mixers have at least one bus, or subgroup, many have up to 10 or more. Buses are, simply put, a routing system. There will be buttons near the fader on each channel for each subgroup, allowing you to assign that channel to one or more of these subgroups. Think of the buses is mini-mixes.
One very common use of a bus is to assign all the drum channels (floor tom, kick, hi-lo tom, hi-hat, snare, etc.) to one bus. This way, the engineer can change the volume of the drumset in the total mix without having to change each fader on each channel. Other uses include groups of singers (girls, boys; leads, harmony), instruments (main, backup; brass, woodwind, percussion), etc.
Just remember that changing the fader on a bus is NOT equivalent to changing the faders on all of its assigned channels. It simply changes the volume of that particular mix of channels relative to the entire mix. Channels can be assigned to multiple buses, and changing the volume of one bus with channel 6 in it will not change the volume of channel 6 in any other subgroups.

Each of the subgroups also has a button allowing assignment to the main mix. In most cases, you will want everything combined into the main mix so that you can control the total volume of everything with one setting. Sometimes, however, you may leave one subgroup by itself; independent of the main mix, for whatever reason may apply. Usually each subgroup will have a left and a right fader, allowing for individual adjustment of the left and right aspects of that mini-mix. The main mix will also probably be stereo. There will be two outputs on the back of the board for left and right mix.

However, some mixers have another button to assign the main mix and any and all subgroups to a "mono" fader. This is another output on the back that is a single bridged out between the right and left of the mix out. This allows you to have a huge amount of possibilities of setups depending on where you have channels and busses assigned and what you have plugged in to the back. The mono will "bridge" the left and right channels, causing all sounds in each to be played in both. It will also, however, leave alone any left/right settings set before it.

VCA's are confusingly similar to buses. However, it helps to remember that buses route, and VCAs are simply a control mechanism. Contrary to subgroups, a change in a VCA will be exactly like moving the faders of all its assigned channels. Thus, any post-fader outs will be affected: post-fader auxes, the level of that channel in any subgroups, etc. If post-fader auxes are used for other main speakers like subwoofers, than a VCA will allow change in those too; where a subgroup would not.
VCA's are found only in larger boards.

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    130 Comments

    Hi

    I'm looking at building my own audio mixer from scratch and was wondering how long the faders should be. I have seen ones at about 75mm but that seems very short? What sort of size is on professional audio mixers? I am also not sure how much to spend on the faders. I would like them to be decent quality and accuracy but not audiophile quality. Let me know if you know of any good brands.

    Thanks

    1 reply

    It would behoove you to look at buying an off-the-shelf mixer. You can buy decent used ones at a good price. Designing and building a circuit board and adding all of the components and case would be a daunting task, and might not give you the desired results that a store-bought unit would provide. All those knobs and faders alone would add a lot to the cost.
    But to answer your question, if you design your own, then it basically comes down to personal preference.

    We live in an "over 55" gated community and we have a theater club. We put on 2 shows a year. I run the mixing board and I have a question about labeling the channels for the microphones. What is the best way? Do I label them in alphabetical order using the character's name, or label them in order of appearance in the play. Any suggestions? We have a Mackie 24 channel VLZ4 .4 bus board. A year ago last spring we did "A Funny Thing Happened On The Way To The Forum" with 19 people miked on stage.

    1 reply

    Ultimately, you have to label the mixer however it makes sense to you. When I ran audio for theatre, I labeled loosely in order of appearance, keeping the leads toward the left side of the board. You can also group people who are exclusively in scenes together and just mute/unmute them as a subgroup.

    For conferences, I like to label each channel with the mic number, because people swap out mics each session. As people get mic'd up, I'll stick their name on a separate piece of tape under the mic number, if I have time.


    Whatever you decide to do, just make sure you label everything clearly just in case someone else needs to jump in! Also, making notes in your script/show flow will make your life easier!

    I really learn a lot from here.....

    Wonderful. You filled in all the gaps that I had: busses and aux.

    Right on! Thanks for this. I've always looked at soundboards as being overwhelmingly complicated, but you really simplified it a lot for me. To the point that I think I could probably tackle one. (I'm going to have to, since we need a sound man for a gig in a couple of weeks, and I've been elected)

    Say i intended to record audio for a soundtrack using electric instruments, is there really purpose of a mixer?

    This is good i really love the instructions. Thank you.

    Although I've seen soundboards in the backs of high school theaters and whatnot, I really haven't had much experience with them. There's so many buttons and switches that it's hard to even focus on any one thing! It's insane how complicated sound mixing can be. Your article really helped explain the audio mixers a lot, though; thanks for all the info!

    http://metrosoundlighting.com/

    Hi, I have an old powered mixer with passive speakers. 400w rms. the desk also has balanced outputs ( XLR male) which i am hoping is like a line out. I am guessing they are for running a signal to another amp to power monitors. I am proposing to run powered speakers from them, i did a test run for 5 minutes but didnt want to damage anything so I halted there. How right am i? the main outs run passive speakers using a speakon connector and as its only an 800w amp ( or 2 x 400w rms) i assume it couldnt split the power any further. I have a gig coming up on the 10th and need an answer. If i was running 400 watts into a 400w powered speaker i assume i would have seen smoke. they seemed to run normally for the 5 minutes i ran them. do you have any advice as to how i can make sure its a line signal? or would it be safe to say it IS a line signal and that i am safe to run as is? any help would be great as i dont have a book on the mixer. thank you so much and please may i have your attention asap. I have googled and googled with no luck.

    1 reply

    it's been a while since you asked so you may already know the answer, but line out is safe for your application. Old mixers sometimes make a little noise/hum out of these outputs. Just be sure not to use amp out or headphones out on old gear. Those contain some amperage usually.

    The Aux section on an Alesis MM8FX is labeled "Send"

    I am beginner to PA system. In our church we are using Yamaha MG 166 CX with two speakers but the performers feel that need a proper feedback. Earlier we were using powered mixer (mixers with buit in amplifiers) with two small speakers. Can I take a out from my mixer (phones) and in to powered mixer. I tried it, it works out but i am looking for a technical guidance will it leads to any troubles. Please reply me.

    1 reply

    Yes you can. A non powered mixer sends out a plain signal referred to as a "line level." A powered mixer should also receive a "line level" which it's getting from your unpowered mixer.

    I'm currently using this same board at a small theatre, however I do not see on it how to make the two FX knobs work as 3rd and 4th Auxes. Any tips on how to make that work? Could I use the subgroups on the board?

    Question about subgroups on using them for podcasting. I have two hosts with mics in to two different tracks. Also, have two computers into the mixer using Skype. I have a mixer that allows 2 subgroups with separate outputs.

    Question is could producer take a call on Skype on one of the computers by connecting her track with 2nd computer track through a subgroup, talk to the guest on Skype (off air) away from main output. Then when the guest is ready change it so the 2nd computer skype guest can be brought into the main mix? Sorry if it is so confusing.

    HI....Great Explanation

    please help me to buy these products...

    i need yamaha 16 channal mixer --- 1

    jbl speakers ---- 6

    shure cordless mics ---- 5

    shure podium mic ----- 1

    suggest the models names to buy....

    1 reply

    A yamaha mg16xu will be good
    and the shure pgx2 with the sm58 mic will be good
    just search on sites like musiciansfriend.com or something

    The best explanation of a mixing board I have found to date. Congratulations. Like *****