Microphone: Some condenser mics have a built-in pad. It attenuates the signal between the mic capsule and the mic’s internal circuit. Because the pad degrades S/N, switch in the pad only if you hear distortion in the mic signal, and the mic’s signal is not clipping in the console.
Effects: Most signal processors have an input level knob and output level knob.
For starters, set the knobs to unity gain. Do the same for the effects-return control in your mixer.
When your mix is nearly complete with effects sends in use, check the processor’s input meter or LED.
If it is showing an overload, turn down the processor’s input level, and turn up the output level to compensate. Do the opposite if the input levels are low.
The goal is to have nominal signal levels in the outboard effects devices, and unity gain through them.
Look for +4/-10 level switches on your console effects sends and in your effects units. Set them to match.
Compressors/Limiters: Similarly, don’t clip the input of a compressor, and don’t feed it too low of a signal level.
Generally you set the makeup gain to match the measured gain reduction. This achieves unity gain through the compressor on the loudest notes.
Electronic Crossovers and Graphic Equalizers: Make sure their clip lights flash only occasionally. Generally they are set to flash a few dB below clip. Some manufacturers say to set the input and output levels to maximum; others say to set them 1/2 to 3/4 up. Check your manuals.
Power Amplifiers: Start with the amp’s level controls halfway up. Set your mix to read around 0 on the mixer meters, then turn up the power-amp level until the sound is as loud as you want it.
It’s a mistake to run a power amp wide open (full volume). If the amp’s input level controls should always be set to maximum, amp manufacturers would not include them. They are there to set proper gain staging.
Turning down an amp’s level controls does not reduce its power. Doing so varies the signal level needed to drive the amplifier to full power. You can still get full power from an amp even with the level controls partly turned down, if the input signal level is high enough. Those level knobs don’t adjust the power level; they adjust input sensitivity.
If you turn an amplifier up to maximum, you amplify any noise coming out of the sound system. Also, you might run the console well below 0 on the console output meters so the house sound is not too loud – but this degrades signal-to-noise ratio.
So, start with your console running at an optimum level near 0 on its meters, then adjust the power-amp input levels for the desired loudness. If your system includes an electronic crossover and multiple power amps, set the level of each amp for the desired loudness from the lows, mids and highs.
SUMMARY
In the console, use a pad only if the gain trim can’t prevent clipping. Get the maximum gain up front, in the musical instrument and in the mic preamp.
If the mixer is not too noisy, turn down the input trim about 15 dB below clipping to create some peakroom. This prevents overload in the following stages.
In any mixer stage or audio component, avoid too-high levels (which sound distorted) or too-low levels (which sound noisy).
Try to keep channel faders, sub faders and master faders near design zero, the shaded portion of fader travel about 2/3 up. The more channel faders in use, the lower they should be set to prevent overloading the mix bus.
With the mixer meters peaking around 0, set the power amp input levels to achieve the desired loudness. Don’t set the power amp levels fully up unless the volume is too quiet otherwise.
By following these tips, you can make your system sound as clean as it can be.
Goodbye noise and distortion.
AES and SynAudCon member Bruce Bartlett is a recording engineer, audio journalist and microphone engineer (www.bartlettmics.com). He is the author of Practical Recording Techniques 5th Ed. and Recording Music On Location.