Sound System Basics

Basic Operation Of A Sound Board

There are certain minimum knowledge requirements needed to be able to operate a PA system sound board. These requirements are not overly difficult and can be mastered by anyone willing to learn a few basic concepts and then listen and apply them to the operation of the sound system. I will be describing the operation of a typical sound board like the one the Shasta Blues Society uses. While other brands of sound boards may have slightly different operational features, their basic layout and controls are fairly standardized. Although there are quite a large number of knobs on a sound board, if you learn one vertical row dealing with just one channel you have learned what 90% of the rest of the knobs do.
Let's start with channel 1.
At the top of the channel row of knobs is the most important control. This knob adjusts the input level of whatever signal is plugged into that channel so that the final volume slider can be operated without moving it to either extreme. This control is what allows many differing kinds of of audio signals to be mixed by just one sound board. As an example, a CD player or the Blues Society organ inputs a very large signal into the board while a guitar or some microphones input very small signals. Any change in this control affects all other levels that come after it.
The next group of knobs, (usually 3 or 4) adjust the tone of the signal in that channel. These knobs adjust the high, middle, (or high mids & low mids) and low frequency content of the input signal.
The next knob is really 2 controls at one position with the inner part adjusting Reverb/Effects, and the outer part adjusting AUX/Mon2 send. The Reverb/Effects knob controls the amount of reverb that is applied to that channel only. Each channels reverb can be adjusted separately. The AUX send control on the Blues Society board has been set up to be a second monitor control and is used to adjust the volume of the monitor speaker(s) that face the keyboard players and the drummers. These are called the back line monitors. This knob can also be used to add additional effects such as delay or compression to that particular channel by sending the signal to an off board processor. On some boards these two functions are controlled by separate knobs and there may be additional AUX Sends to accommodate more than one extra processor.
Next is the primary monitor control knob that is used to adjust the volume of that channel in the 2 floor monitor speakers that face back at the performers. This is the main control to allow the vocalists to better hear themselves. Both the Mon. and the AUX/Mon2 controls are independent of the channel volume slider and can be adjusted without affecting the house sound.
The next knob is call a Pan Control. If we were operating the board in the stereo mode, this knob would be adjusted to position the sound of that channel left or right as needed in the stereo mix. If the board is run in the Mono mode this control is set to the 12 0'clock position and no further adjustment is needed.
The last control on the channel is the volume slider. It adjusts the loudness of that channel in the house speakers. This control is independent of and has no affect at all on the two monitor volume levels. At the very bottom of the channel row is a label that tells the operator just what signal that channel controls.
The only control that affects both the house sound volume and the two monitor levels is the first knob on the channel, the input gain control. That is why it is the most important control.
Moving from the individual channels, 1 through 16, to the right hand side of the board, we come to the Master Control section. It is here that we control the overall sound and volume of the mix.
While there are many knobs and 4 sliders, for right now we only need to know about the sliders and some of the knobs. Two of the knobs are in the top area of the master section and control the overall reverb and the amount of reverb in the house speakers. They are labeled Rev Send and Rev to Main and since these are master controls they are usually set to the 12 o'clock position and any further adjustment is done at the individual channels.
The third knob is labeled AUX Send and is the overall volume control for the backline monitor speakers or it can control the level of the signal that is sent to an effects processor. If the AUX Send is used as an effects send then the knob labeled Effects Return is used to adjust the level of the returning processed signal to the mixer before use by the individual channels.
The Left and Right sliders are set to the 0 mark along the side of their travel. No other adjustment is needed if the system is being run in Mono. The Main slider is set a little below the 0 mark and is adjusted only if the overall volume in the house speakers needs to be raised or lowered. If the system is being operated in Stereo then the Left and Right sliders are the controls that are adjusted to change the house volume. The Mon. slider is also set a little below the 0 mark and is adjusted only if the the overall volume of the front floor monitor speakers needs to be raised or lowered.
The only thing left is the hook-up of the audio snake to the sound board. Everything is usually either color coded or numbered. In the case of the Blues Society board the wires coded Red are to the house speakers and are plugged into the jacks with the Red label. The wire coded Green is the Mon 1 signal to the power amp at the stage and is plugged into the jack coded Green and labeled Mon Out. The wire color-coded Yellow is the Mon 2 signal to the power amp and is plugged into the jack coded Yellow and labeled AUX Out. If this output were to be used as an effects send instead of a second Mon output, the signal would be routed to an effects processor, such as a delay unit, then back into the mixer at the Effects Return jack. The remaining wires are numbered 1 to 16 and are plugged into the corresponding channel input jacks of the same number.

With an understanding of the function of the controls that I have discussed and some additional training, anyone interested in running live sound on a mixer like the Blues Society's should be very successful and find it an enjoyable experience.

David Thompson