Distortion is not as big a problem as it was 30 years ago (and oddly enough is often now used as an effect to add warmth and size to an input that’s too clean), but it can seriously degrade the sound of an input. The distortion we’re talking about here is caused by poor gain structure somewhere in the audio signal chain. If the channel’s input preamp is turned up too much and you’re seeing red lights and peaking meters, you may also hear distortion of the voice or instrument along with the blinky lights. An easy remedy is to back off on the preamp gain, re-balance input and output fader levels to achieve the desired volume, and the distortion should disappear.
A common place for gain structure to go wrong and distortion to be introduced is with wireless microphone systems. Let’s say you have a wireless handheld transmitter and receiver combo. They usually have level adjustments on the transmitter as well as the receiver. Set the transmit level too “hot” and the receive level too low to compensate and you may hear some distortion – if the voice sounds fuzzy and squashed, this may be what’s happening. Ensure that the levels on the transmitter are strong but shy of peaking, and then adjust the receiver level to attain a clean output level to the mixing board.
Poor gain structure can be the cause of many other unwelcome noises in the signal chain. If you don’t adjust input preamp levels to a nominal level, let’s say 0 dB on the input meter or that first yellow light, and then you turn up the fader to +10, and the master fader to +10 to make up for the low preamp level, there will probably be audible hiss in the sound system.
The same goes for hums and buzzes that can accumulate across inputs on stage. If the acoustic and bass guitar have a small “rizz” because of a bad cable or poor grounding of the electrical service in the venue, these noises are doubly noticeable if you’re practicing poor gain structure techniques.
Polarity & Phase
It’s tempting to use more than one mic for a kick drum, snare drum and/or guitar amp. The benefits are many if they’re dialed in to work well together, but bad things can happen if they’re not.
A snare with a top and bottom mic is the easiest of these scenarios. Because the mics are mostly pointing in opposite directions – down on the top head and up to the bottom head – a simple polarity reverse on the input channel of the bottom microphone generally gets them working together for a fatter midrange and fuller low-end. If you start with the top mic only, then add the bottom mic and the fullness goes away, chances are you haven’t reversed the polarity of the bottom mic. If you have, the two mics may not be wired the same or you have a mis-wired mic cable or snake line.
When it comes to using two mics on a kick drum and/or guitar cabinet, or a bass DI blended with a bass mic, things can get tricky. There are a few simple rules to avoid frequency cancellations that occur because of phase problems caused by timing/position offset.
Rule number 1: Always listen to one input at a time before combining them. If one input sounds great on its own but starts to sound “hollowed out” or thin when you add the second input, chances are there’s a polarity or time arrival issue.
Rule number 2: Flip the polarity of one channel or,
Rule number 3: Use some input delay to get the two channels to work together. If you’re pressed for time, I recommend using just one input to get started, adding the second input only when there’s time to align them. Be cautious when combining similar inputs and be on the lookout for frequency cancellations due to non-aligned mics or sources. The frequency cancellations can sometimes occur in the highs or high-mids, but when the low-mids or lows cancel, it’s pretty easy to hear – if you know what you’re listening for.
This brings us back around to where we started. Listening critically is a skill that takes years to master. I’m not going to overdramatize by saying it’s like performing surgery or flying a plane, but I don’t want a first-timer doing either one of those things, so it’s a good idea to have some “hours in the cockpit” before mixing through a huge sound system in front of 20,000 people.
Practice, practice, and then practice some more. Get familiar with how 500 Hz sounds compared to 2 kHz. Start slowly by recognizing the difference between low-mid frequencies on a guitar compared to high-mids. If you have access to a mixing console, listen in headphones and play around with the parametric EQ to hear the changes that happen as you sweep frequencies. Then crank up the preamp level (very carefully, mind you) and create then identify distortion. Play with various gain structure scenarios and listen for hiss and buzz problems when you don’t follow the rules.
If you don’t have access to a console and PA system,
I’d be happy to share my frequency recognition cassette with you – that is, if you happen to still have a Sony Walkman stored in an old shoebox in the garage.