As the complexity of mixing consoles continues to grow to meet the demands of contemporary worship services, it becomes a challenge to find experienced sound technicians. Learning the function of each control in a sea of knobs can seem daunting; and learning how to adjust those controls for optimal performance can seem overwhelming. But take heart, understanding how to get good performance from your mix console need not be difficult, once you have a basic understanding of how it operates.
We will begin this task by exploring sound system gain structure. (engineers are required by law to use fancy terms to describe simple things) Optimizing gain structure means nothing more than learning to set the controls on the mixer so that what comes out is as quiet and distortion-free as possible.
While we are at it, lets get some more technical baggage out of the way so we can get on to the good stuff.
• Signal – An electrical representation of a sound as it passes through electronic equipment.
• Volume – How loud the sound is
• Level – The electrical equivalent of Volume
• Gain – Another way to describe making a signal stronger (a measure of signal level increase).
• Noise – Any undesired sound that your sound system creates, even when a sound signal is not present. (hiss or hum)
• Distortion – An undesirable alteration of the signal (clipping)
That wasn’t so bad was it?
Passing an electrical signal through a piece of audio equipment requires walking a line between two audio evils, noise and distortion. All audio equipment adds noise. If the audio signal is small, the noise becomes a significant part of the signal. To keep our audio signal as clean as possible, we need to make sure that the signal is strong from the very first stage.
On the other end of the level spectrum, there is a limit to how large a signal can pass through an audio circuit undistorted. Like driving a big truck under a low overpass, if it doesn’t fit, some rather ugly clipping results.
So to keep our audio signal safe from harm we must keep it strong ALL the way through the mix console, but at a level low enough to prevent distortion. Fortunately, the mix console designers have kept this in mind and made this easy to achieve.
One of the most important tools that we have on a mix console is the audio level meters. When the audio system is running at its loudest, the output meter should peak at ‘zero’ or slightly above. Under these conditions the signal level at the output of the mixer is at its optimum. If the meter never reaches zero, and noise is audible coming from your speaker system with no audio signals present, you may wish to reduce the gain at the power amplifiers or crossover to bring the system gain into balance. Furthermore, if you have trouble getting enough signal level from the mixer to tape your service, you may want to make this adjustment. If you have a biamped or triamped system or are unsure of this adjustment, get a professional to help.
Now lets look at signal flow through a mix console and the controls that adjust the signal level. The input channel controls are ‘Gain’ or ‘Trim’, Pad, Equalization and the level Fader. The master Faders control the gain in the master section. The figure below shows this basic signal flow diagram.
With all of these controls, how do you adjust them? In the example with the meter and power amplifiers, adding gain later in the chain only leads to more noise. If we adjust the microphone preamplifier gain, so that the signal exits at the proper level and set the faders so they do not change the gain (unity gain), the mixer is working as it was designed. How can you tell where to set the faders? Most console manufactures label the ‘unity’ gain position with a ‘0’ in the upper part of the scale. Now let’s see how easily this can be put into practice.
An easy procedure for setting up a Mix Console:
• Turn down all of the channel gain trims. (optional)
• Set the input channels faders that will be used and the master faders to ‘0’.
• Adjust the gain trims on each channel for the ‘proper mix’ at the proper sound level. (leave the faders alone and adjust the mix with the trims)
• If an input is too loud with the fader at ‘0’ and the gain trim is down, engage the input pad.
If the rest of the system gain is set correctly you are done. With the faders at ‘0’, there is still room to increase or decrease the inputs as necessary to adjust the mix. Don’t become obsessed with keeping the faders on the ‘0’ mark. However, if the fader is always near the top or if it is 10 dB or more below the zero mark, which can lead to distortion, readjust the gain to return it the proper range.
Just remember to keep your faders near ‘0’, don’t be afraid of the gain trims, and then noise and distortion should become a thing of the past. By reducing the distraction of noise and distortion, a properly adjusted mix console is an asset to the worship service.