Audio Basics
Stage Monitoring Simplified: mixing monitors and
house simultaneously
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Encompassed in today's live show are several individual shows, for example, light shows, laser shows and more. It's not uncommon for each of these independent shows to have its own set of engineers. The focal point is the band/artist, and they're the reason all of the other shows are taking place. And, it should be pointed out that most of these "shows within the show" are presented for the audience. Good engineers realize that the monitor mix is a show in itself. It's the only show that the musicians get to hear, and it certainly is the mix that most affects their performance. Big shows usually have a separate engineer for the monitor mix, but for average shows one valuable individual functions as both the front of house (FOH) and monitor engineer. To accomplish a good monitor mix, you must understand your particular mixing console; we can, however, examine some basic principles that apply unilaterally. While working your magic behind the FOH console, most people don't realize the work you're doing for the musicians. |
The musicians also have to hear the performance, except they usually want to hear something totally different than the house mix.
In fact, many bands have members that each want (or even require) a different mix than another band member. That means multiple mixes, all running at the same time, which can present some challenges to the engineer, because all of these mixes cannot be monitored simultaneously. Most consoles allow toggling between each of the mixes, allowing you to make changes to each individually. This, of course, depends on what features the console has and how you, as an engineer, decide to accomplish your monitor mix. Let's first take a look at some obstacles you may encounter in your equipment.
SNAKES, SENDS & RETURNS
The snake, of course, is the multiple input cable that all of the instruments plug into on the stage. The cable then is plugged into the console to carry the signal from the stage to the mixing console. The snake also has "returns," which, as the name implies, route signal from the console back to the stage and musicians.
The amount of returns available will directly affect the amount of signal that can be routed back to the stage. For example, a 24 x 4 snake offers up to 24 pathways to the console from the stage, and four pathways back to the stage from the console. With four return paths, the possible combinations of mixes are four independent mono mixes, two stereo mixes or one stereo mix and two mono mixes.
The more return paths, the more possibilities you have to run monitor mixes. Bear in mind that these return paths also must carry the signal to the main loudspeakers.
Another limitation that can be encountered is the amount of pathways that a mixing console has to use as returns to the stage. A 24 x 4 x 2 console has 24 inputs for instruments, four buss (or group) outputs, and a pair of outputs for the mains. Buss or group outputs (sometimes called sub-outs) can be used as monitor return outputs.
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Four-buss outputs would yield the same combination of possibilities as a four-return snake. Obviously, more buss outputs equals more possibilities for this type of monitor mix. Probably the method with the most possibilities is routing monitor mixes with the auxiliary sends. Like busses, auxiliary or aux sends can be used to route monitor mixes. Although aux sends are used for routing signal to effects processors, they are very useful in running monitor mixes. For aux sends to be useful as monitor mixes, they must be able to be used in what is known as pre-fader mode. There is usually a button next to the aux send pot on each channel that will allow you to switch between pre and post-fader modes. Keep in mind that for each mono return path, a separate amp at the other end for a power source is needed. Stereo requires a two-channel power amplifier, or a separate amp for the left and right sides. Have you checked your equipment for features? To make it easier to describe some basic techniques, we need a typical scenario. |
Let's assume we have a 24-channel input console with four buss outputs and at least four auxiliary sends. Our console is also equipped with a stereo headphone output, so we can listen to each mix separately without listening to (or affecting) the house mix. Most consoles possess this capability because it is necessary for the engineer to listen to alternate mixes during a performance.
Our snake has 24 channels with four return paths. Let's also assume that we will be running a stereo house mix. To achieve a good monitor mix, there are several ways to get there. So, let's take the trip.
GET ON THE BUS(S)
Each channel has a feature that will allow assignment of its signal to a group or buss out. These assignment groups include the main L/R buss. The main L/R group will be used to route signal from the console's main output jacks on the back of the board through the snake's first two returns. The faders on the console labeled "mains" or "L/R" (or something similar) will control the amount of signal. The returns from the snake on the stage side will be routed to the stereo power amp (or amps) that powers the main front of house speakers. This way, the signal from the power amps takes the shortest path to the speakers.
In addition to the main L/R outputs, a four-buss console has four additional outputs that correspond to faders that control the signal routed to them. The faders are typically labeled "buss 1,2,3,4" or "Sub out 1,2,3,4" etc. Each channel has a switch, which allows you to assign its signal to a particular buss. With this configuration, we could run a stereo monitor mix. If we decided to do this, we would assign each channel to busses 1 and 2.
The output of buss 1 will be routed through the snake's return 3, and the output of buss 2 output will be routed through return 4. Remember we're using returns 1 and 2 for the main house mix. Return 3 will be routed to the amp that powers the left side of the monitor mix and return 4 to the right side.
I only recommend doing a stereo monitor mix if in-ear monitors are to be used. Most applications require the use of on stage loudspeakers (monitors or wedges). For this reason, it is a good idea to run a mono monitor mix. Monitors on stage would normally be too complex to run a stereo monitor mix. By assigning all of the instruments to buss 1, we can be sure that all of the stage speakers represent an overall mix for all of the musicians on stage.
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Because we are only using buss 1 for this mix, we could then use buss 2 for some accent monitors on stage. For example, if all of the musicians can hear the overall mix, we could assign only the vocals and other lead instruments to buss 2 and route that buss to spot monitors for singers (who like to hear themselves heavily in the monitor mix) as well as other lead instrumentalists who cue off of each other. If we had more returns in our snake we could even provide accent monitors for the bassist and drummer/percussionist, for example, by using busses 3 and 4. One limitation of using busses for your monitor mix is that if you assign a particular channel to a buss, you might not be able to route that signal to another buss or at least not the buss you need. Another limitation is that on some consoles, you cannot adjust the amount of signal that each channel contributes to each buss. That means that whenever the buss is assigned, the entire signal from that channel is routed to that buss assignment. The amount of individual signal from each channel to the buss is determined by the position of the channel fader. Many manufacturers design features that allow for more possibilities; however, that usually means more circuitry, hardware and board space for additional faders or pots. More features means more expensive. This is a quick and easy way to run monitors, but there are other avenues that lead out of the console - the auxiliary send outputs (aux sends). |
WORKING THE AUX SENDS
In addition to buss output jacks, mixing consoles also have output jacks that correspond to their auxiliary send pots. Remember that our sample console has at least 4 auxiliary sends. Each one of these channels has a level adjustment pot for each of the sends. The console will almost certainly have an aux master section that will allow for control of the overall signal level of each aux output. The aux 1 output jack should be routed to the snake's return 3. Aux 2 out should be routed to the snake's return 4.
We still need to use returns 1 and 2 for the house mix. By utilizing the aux sends, we can accomplish two mono mixes. Each of these mixes can contain any amount of each channel. For example, if we want more of channel 9's audio in the aux 1 mix, we simply turn up the aux 1 pot on channel 9. By using the level adjustments for aux sends 1 and 2 on each channel, we can create a mix that is suitable for the lead instruments on aux 1 and a completely separate mix that is suitable for the rhythm section on aux 2.
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One feature that our mixing console must incorporate is that ability to route the sends in "pre-fader" mode. In pre-fader mode the position of the volume faders on each channel has no affect on the level being sent down each of the aux sends. This means that if we turn down the lead guitar in the house mix by lowering the channel's volume fader, the monitor mix will not be changed. Once again, if our snake had more return paths, we could utilize additional sends for more on stage monitoring possibilities. |
By assigning the aux mixes one at a time to the headphone outputs, you can make adjustments to each mix without affecting what the audience hears. In addition, by routing the signal outputs of our effects processors to channel inputs, we can send some effects to each of the monitor mixes. For example, by routing the outputs of a reverb processor to the inputs of channels 23 and 24 of our mixing console, we can send an adjustable level of reverb to each of the two monitor mixes by simply turning up sends 1 and 2 on those channels.
Be cautious of routing signal from channels 23 and 24 back to the inputs of the reverb unit as this will result in an electronic feedback loop. If you use send 3 and 4 for the inputs to your effects processors while using channels 23 and 24 for your reverb returns, turning up sends 3 and/or 4 on these channels will create this kind of loop.
Using aux sends for monitor mixing is probably the best and most popular approach as it affords the engineer the most versatility and functionality. Hopefully, this article will arm you with some of the knowledge critical in implementing some basic rules of audio. Always make sure you know the equipment you own and the equipment you intend to buy. Good luck, and have fun!
Scott Foulkrod has a degree in audio engineering and currently teaches audio engineering at Houston Community College in Houston, TX.
January 2003 Live Sound International