Do you ever hear hiss or distortion in your PA? You may not have faulty equipment! After working in many churches and schools there is one common problem people have with their PA system. This issue is gain structure. Setting up your console with the proper gain structure is very important and being done correctly can save you lots of headache and money.
The Technical Information
First let’s discuss a few words you may hear sound guys throw around. Words like headroom, unity, gain, trim and fader. Headroom is the amount of volume you are able to add above normal operating volume. It is important to have a good amount of headroom. Gain/trim is referring to the volume knob on the top of any channel on your mixer. The gain is your input volume to the channel. This knob is very sensitive and can increase/decrease volume quickly. The fader is the secondary volume control at the bottom of any channel. This is where most of your mixing happens and is intended for small/smooth volume changes. Unity refers to the point where there is no volume added or subtracted on the fader. Unity is marked 0db on the mixer. This is also known as the “sweet spot” on the fader. Any changes in volume in this area will be smoother and less noticeable to the listener.
How to fix your gain structure!
1st you will want to have your mixer completely zeroed out. Turn all your gain knobs and faders all the way down and set all the eq knobs to 0db (you may hear engineers call this a flat eq).
2nd set your master fader to unity (0db). There are many times I will come across a mixer that someone has set the master too low and each channel gain too high. This causes hiss and distortion. With the master fader set to 0 you will be starting with the output of your mixer neither adding or subtracting volume.
3rd make sure your channel is all zeroed out and the master fader is set to unity (0db).
4th bring your channel fader up to unity and ask your singer/musician to play or sing. While they are singing begin to turn up the gain knob until a good volume is heard in your speakers.
You now can leave the gain alone and mix from the fader. It’s that easy! Be sure to watch your channel meters and clip lights. If your gain is too high you may start clipping the channel. This is where distortion and possible damage can occur.
Thanks for reading!