The Mixing Console in Worship

By Leon Sievers
Sound Professional
December 03, 2018

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The mixing console can be an intimidating and "phobic" experience for a new sound tech.Modern consoles can feature more than 500 knobs and infinite settings. However, operating a mixing console can be a very rewarding experience once you understand the basic principals of signal flow. Every console, regardless of size, can be broken down into either an INPUT or CONTROL section.†

The INPUTS or channels strips are available in both MONO and STEREO configurations. It is important to consider this when evaluating a console for your particular application. MONO inputs accept either a mic or line level input and the fader controls a single signal. Many consoles feature a number of STEREO inputs, which accept only line level inputs and control two channel inputs from a single fader. Donít automatically assume that a 32-channel console offers 32 microphone inputs when often several channels are reserved for line level devices such as CD players, DAT machines, etc.

The Input or Signal Trim is usually the first knob at the top of the channel strip; this level control allows you to adjust the level of the incoming signal from a microphone or instrument. Proper adjustment of this control maximizes the signal to noise ratio of the signal. All sources put out different amounts of signal. Some may be weak and others quite strong. If there is too much, distortion will result. On the other hand, if there is too little, the channel level may have to be set much higher than the rest of the channels. The input is usually adjusted in conjunction with an LED Clip indicator or VU Meter, which is used for setting the Gain/Trim/Pad. This LED is designed to illuminate when the input signal is approaching the upper limit of the input circuit's capacity, but still leaving around 3dB of headroom in most cases (check the manual to be sure). It is thus possible to set the Gain controls simply by watching the channel Clip indicators during a sound check and adjusting them for slight amounts of activity.†

Aux Sends are simply what the name implies, an auxiliary send of the audio signal or source input for that channel strip. On mixers with "Pre/Post" EQ selector buttons for these controls, they will come after the EQ section, otherwise they will be right after the Gain, Trim, etc. This extremely versatile "knob set: allows you to route the channel signal to an outboard effects processor, recording device, assistive listening or broadcast output. Additionally Aux Sends are often used to provide a separate mix for the stage monitors. The reason for there being more than one Aux Send control on the channel and more than one Aux Master Control is so that you can mix for more than one monitor system. The drummer, for example, usually needs to hear himself and the vocals extra loudly, and the vocalists, of course, need to hear themselves very loudly while the guitarist might want to hear a predominance of bass and keyboards because his amp is almost all he can hear.

The EQ or Equalizer section usually follows the Aux Sends and is usually desirable only on that portion of the channel signal headed for the FOH system.†

For example, stage monitors operate in a terribly demanding acoustic environment - speakers are close to mics and everything tends to be very loud. As a result, the best way to mix for monitors is to treat them as a totally independent system. Large concert PA's usually have a separate monitor mixer and someone to run it. Smaller systems still need to treat the monitor mix as separately from the main mix as possible. That is why the channel signals would not, as a rule, be EQ'd before being sent to the Mon/Aux busses. That way, the only equalization they get will be specifically for the stage monitor system.

For that reason, some mixers have Aux Send controls after the EQ with "Pre/Post" selector buttons to put the desired ones through the channel EQ ("Post") or to bypass it ("Pre"). In other mixers, one or more of the Mon/Aux controls may simply be after the EQ (i.e. "post EQ") and are therefore permanently affected by it.†

All EQ's function by altering the gain above or below normal over various frequency ranges. Some mixers offer "semi-parametric" EQ. This usually comes in the form of one or more cut/boost controls, each with a frequency control to position the cut/boost exactly where you want it along the frequency spectrum. One application of such a feature is in the fight against feedback. Here you would turn the cut/boost control counter-clockwise to produce a "dip" in the frequency response, then rotate the frequency control until the dip reaches the guilty frequency and the feedback is reduced.†

The SWEEP control determines what range of frequencies is affected by the MID cut/boost. It moves or "sweeps" the MID control's peak or notch in response all the way up to several thousand Hz or down to below one hundred Hz. As a result it can have quite a noticeable effect on the sound especially since the MID cut or boost will be interacting with whatever cuts or boosts you may have set with the LOW or HIGH EQ controls. If you have set a LOW boost, a MID boost swept all the way down to the lowest frequency setting will alter the sound of lows AND increase their volume. As music plays through a channel on the mixer and speakers, adjust that channel's MID, first for a boost then for a cut and SWEEP them back and forth. (If there is no MID cut or boost setting, i.e. if it is set at the center position, the SWEEP will have no effect at all). Now repeat the process with that channel's LOW and HIGH EQ controls at various settings (but with the volume at a safe level for the speakers).†

Most EQ sections include an optional High Pass Filter, which inserts a Low Frequency Cut at a pre-selected frequency usually at or near 80Hz. By invoking the HPF you automatically attenuate these lower frequencies. This feature can be very useful in cleaning up the mix by removing ambient low frequencies from open vocal mics.

The Pan control found only on mixers with stereo Main outputs, functions a bit like the "balance" control on a home stereo system. In fact it regulates how much of the channel's post-EQ signal gets routed to either the Left or Right Main PA busses. If, for example, the Pan control is rotated all the way left, that channel's signal will only go to the left Main buss. If the F.O.H. (main) PA is stereo, only the speakers on the left side of the stage will be producing that channel's output - not an ideal situation. In most PA situations, the only real reason for running a stereo F.O.H. system is to get the sonic benefit of a stereo reverb. However, if you have a basic stereo mixer with a "Main" master and corresponding mono output, and you are running a mono F.O.H. system, the PAN controls can be used to establish two main mixdowns, perhaps one for the live sound and the other for recording.

The Pre-Fade Listen or PFL/Cue button sends post-EQ channel signal to the headphone amplifier so those individual channels can be isolated through the phones. Because the PFL/Cue signal is tapped off just before the channel fader (hence "pre-fade") you can shut that channel down through the FOH PA, but still hear it through your headphones. This is a convenient feature for previewing channels before bringing them into the mix (eg., for cueing tapes up). It may also be used for checking out problems - a squealing amp, a distorted mic, etc.†

The Mute button is usually inserted just after the EQ section. I mention it at the end of the channel section simply because that is where the button most often appears - i.e. conveniently close to the channel fader and PFL/Cue button. As the name implies it silences the channel through the FOH system and possibly the monitors (check your manual). Its prime function is to enable the user to pre-set a channel's level, then shut the channel off to be added to the music program later on. Muting is a convenient feature for infrequently-used channels such as harmonica mic, acoustic guitar, banjo, mandolin, certain wind and percussion instruments, pre-recorded music or sound effects, all of which should be left off when not in use to reduce unwanted sound pickup and the risk of feedback.†

And finally the Fader or level control is the slide control that allows you to adjust the amount of signal that appears ion the main mix. While the trim control is used to adjust all of the incoming signal levels to be nearly the same, the fader allows you to adjust the relative levels of each channel being mixed to the master mix buss. Usually adjacent to the channel fader, are the Submix sends, which allow you to assign the channel strips to the master subgroup faders. For example you may wish to assign all of the drums and percussion to one group and the background vocals to another. This method of mixing enables you to control the relative levels of groups of microphones with just one fader in the master or control section.

The features of the master or Control section of the mixing console generally act as output level controls for their designated output connectors, one exception being the Aux Return master(s) since those jacks are inputs. Aside from that, everything does exactly what its name implies. Check the owners manual for your specific console for more detailed information on any of these features.†

The Sub Group masters regulate the Sub mix or Group output levels, which are assigned by each channel strip. When a console is properly adjusted it is possible to mix entirely from the Sub Group faders which each control entire groups of input channels. The Main output(s) regulates the output of the MAIN, SUM or MONO buss where the outputs of the Sub or Group busses or Left & Right stereo master busses get mixed down into a single signal which is delivered to the amplification system.

The Aux Send masters regulate the output level of all of the channel strips, which are sending signal via the Aux Send. This control is used to set the output level of the signal being delivered to effects rocessors, recording devices, etc. The Aux Return masters regulate the input levels of their designated RETURN jacks such as the signal being returned from an effects processor. The effects return offers a convenient method to blend the level of the effects device back into the main mix.†

A mixer may have 12, 24, 36 or upward of 56 channel strips. Thatís a lot of knobs! But rememberthat most channel strips are exactly alike, and once you learn the features and operation for a single channel strip. Therefore you can simply repeat the process for the input, aux send and eq for each channel strip, bearing in mind that each instrument or vocal will require itís own unique adjustments.

One of the best ways to become familiar with a console is to spend a some time in practice. First, you'll need a sound source, or a selection of sound sources. There are two types of sources you could use: one is an acoustic source picked up by a microphone; the other is a direct source, such as tape or CD. I suggest you begin by using a tape or CD player, connected to a line input of your mixer. You'll also need decent headphones or some good quality studio monitors connected to the control room or main mixer outputs. By monitoring the console output as directly as possible, you will be able to hear qualitative changes as you make them - including subtle differences room acoustics or ambient noise would otherwise obscure.

The idea is to send your program source through an input channel, play with the various channel controls (EQ, pan, etc.), and monitor the results. You may want to connect your source to a stereo channel to do some of your tests and then connect to a mono input to discover the differences. The stereo and mono inputs may differ, for example, in the EQ control available. Also, listen to how the pan (or balance) control differs on a stereo channel from the pan on a mono channel.

The area you'll want to spend the most time with is the EQ. Listen to a variety of program material to determine how your mixer's channel EQ affects the sound of the signal. Some of the best recordings to use include male speaking voices and solo recordings of piano, violin and guitar. The higher the recording quality the better, but almost any recording will give you some idea of what your EQ will do.

Using recorded sound as your source, rather than a microphone on a voice or instrument, provides exact repeatability for comparison of different control settings. It also allows you to hear only what the mixer settings are doing, without the confusion of hearing direct sound from the stage.

One factor that should make the sea of knobs in front of you a little less imposing is the fact that during a typical church service, relatively few controls need to be touched. Many of the controls on your console are used to pre-adjust levels or determine the destinations to which signals will be routed. It is not unusual for an operator to use only the mute buttons and faders during a service. Trim controls should be set in advance and need to be adjusted only if conditions change dramatically. Likewise, channel assignments to sub sends or main outputs are normally set and left alone. Once channel EQ adjustments have been made for particular microphone, there should be no further need to adjust EQ during the service.

Of course, there's a lot more to mixing sound than we can get to in this article. That's what Sound Advice is for. In the future we'll further explore what it takes to provide the best sound possible in your worship service.









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