On a basic mixer every knob is a volume control. On a bigger board there may be some special function knobs. The thing that you must understand is that when you twist any knob you are affecting the volume and the mix.
From the top of the mixer channel strip we usually see a gain control, several eq controls, auxiliary send controls, a pan control, and the channel fader. The aux controls do not control volume in the main mix, but they do control the send level to various other areas.
The Auxiliary Send Section
If monitors are run from the house board one or more of the aux sends will be used for that purpose. If there are outboard effects the aux sends will control the amount of the channel input that is sent to that particular effect unit. Sometimes aux sends may be used for a different mix for a special use, such as for a limited recording or to send to another sound system in another part of the venue.
Aux sends may be pre fader or post fader. Pre fader sends are used if monitors are run from the house board. Post fader is usually used for sends to effect processors and for some other aux send applications. Some boards allow the patch position to be switched between pre and post on an individual channel or a global basis. They may be set up pre or post eq. This patch point is not usually switchable on an analog board, though some allow for switching with internal jumpers. A digital board may give you full control of the patching through virtual patching controls.
The Gain Control
The gain control knob at the top of the channel strip can be considered the preamp gain control. The purpose of this control is to match the channel strip with the level of the incoming signal. The gain control effects the whole channel strip. If you are running monitors from the house board a change of the gain level will affect both what you have in the channel and what the musicians hear in the monitor.
The control should be set so that the signal feeding the channel is relatively high without overloading the channel. You do not want to see peek lights lighting in the gain control are, as that will produce distortion, but too low of a level can increase the noise in the channel strip.
The EQ Section
There are usually at least two, and sometimes several more knobs in the eq section of the channel strip. There will be a low and a high eq even on the most basic mixers. The next step is to add a mid eq or two. On more advanced mixers there may also be sweep controls and Q controls or switches.
The sweep control adjusts the center point of the effect of the eq band with which it is associated. If there is a Q control or switch it affects the width of the signal spectrum that is effected by the control. If there is no sweep control the center frequency or turnover frequency is fixed.
The high (treble) and low (bass) controls are usually set up as shelving controls. This means that they effect all frequencies above or below their turnover point. Mid controls produce a bell shaped curve around their center point. The level controls affect the amount of boost or cut for their bands of influence.
The eq controls are selective volume controls. If you turn all of the tone controls up the effect is similar to pushing the channel fader up. If you cut all of the eq controls the effect is similar to pulling the channel fader down. Sometimes when you think that something is not quite loud enough in the mix you can make a small adjustment in the eq section to make the instrument or vocal stand out in the mix without moving the channel fader. When you adjust an eq control you may need to also adjust the gain control or the channel fader to compensate for the change in the eq section.
The Channel Fader
The channel fader is the primary means of real time level control. This is the go to knob when the vocalist can't be heard or the guitar player switches from a distorted sound to a clean sound and threatens to peal the paint from the walls. The channel fader controls the level in the mix and any post fader aux sends. It does not affect pre fader send levels.
Channel faders are often set up with an expanded section near the 0 db point. In this region a given control movement will have a smaller overall effect on the output of the channel. This helps to fine tune the mix. When setting up the mix it is usually best practice to keep the channel faders near the zero point and adjust the gain controls to provide the proper amount of signal at that point. Then use the channel faders to fine tune the mix or to pop a solo out of the mix at the proper time.
The Things to Remember
Most of the controls on the channel strip will affect the output of the strip in one way or another. The gain control has an effect on the channel output and the outputs of the various aux sends. The eq section is a frequency variable level control. The channel fader is the primary level control for the channel strip in the final mix.
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