In thinking about the church sound systems I’ve worked on over the course of my career, I realized that the vast majority of the problems I’ve encountered can be boiled down into just a few categories. If a church asks me to address a problem, odds are that it was caused by one of the following issues.
1. Gain Structure
This is of paramount importance in an audio system, to the point that if it’s wrong, it almost doesn’t matter if everything else is right. In simple terms, every component of a sound system is designed to operate with signals of a certain level. Too high, and the signal becomes distorted when the device overloads; too low, and the signal becomes swamped in the noise floor.
We generally classify audio devices as operating at one of three signal levels: mic level (obvious…), speaker level (also obvious) and line level (everything else). Mics put out a very weak signal, on the magnitude of a hundredth of a volt or so, simply because the air pressure variations they’re picking up are not very strong to begin with. So as soon as the mic-level signals get to the console, they hit the preamp, which boosts them up to a more reasonable level.
From this point on, we’re operating at or around line level, which in the professional audio world is +4 dBu (1.23 volts) or thereabouts. We hang out at line level all the way until the signal leaves the power amplifiers, which boost both voltage and current significantly. We’re talking about levels of power that can rival what comes out of the receptacles in your home. This is appropriately named speaker level, and should be treated with respect.
Within the realm of line-level signal flow, which is where our audio signals spend most of their electronic existence, it’s extremely important to pay close attention to how the signal level changes as it flows through the desk.
Every piece of audio equipment known to humanity has a maximum signal level it can accommodate (usually around 10 volts rms for pro devices) and a noise floor which, as long as we occupy this physical universe we do, can only be reduced to a point.
If the signal level is too high at any point in the chain, distortion may be added to the signal as a result of overload and we’re stuck with it for good, regardless of what we do downstream. A common example: let’s say we set the mic preamp gain too high, and the signal is clipped as it comes in. We can lower the channel fader to attenuate the signal back down to a reasonable level, but now it’s just quieter and still distorted.
Likewise, if the preamp is set too low, the signal-to-noise ratio (SNR) will be poor, and the signal will be noisy and hissy. We can boost the signal later on, but we’ll be boosting the hiss, too. So it’s very important to get the signal level right at every point, in order to avoid causing problems that we can’t reverse later.
Optimally, every device in the signal chain would overload at the same time, meaning there’s no headroom bottlenecks anywhere. If the console meters are at -10 dBu (most analog desk meters read in dBu, even if they don’t say so) and the amps are clipping, that’s no good. Likewise, if we’re slamming all the faders up to the top of their tracks and we still can’t get a decent level into the amplifier, that’s a problem as well. The goal is to get the signal level into the “sweet spot” (engineer-speak: “nominal level”) as soon as possible and keep it there.