LIVE SOUND
Travis Stoddart is an audio engineer , live sound tech , and system design consultant . He is based out of London , ON and runs his own business , Alleyway Productions , as well as authoring the blog The Home Studio
Archive . He can be reached at alleywayprod @ gmail . com .
By Travis Stoddart
Understanding Complementary EQ
Q uickly creating a good mix can be one of the toughest aspects of doing live sound , especially at showcases or festivals where sound checks are often brief and by no means comprehensive . Thankfully , this challenge can be made easier with one of the most readily available tools at an engineer ’ s disposal : an equalizer . With thoughtful use , even the most basic equalizers can be used to carve out a spot in the mix for each instrument and voice .
The Theory To understand complementary EQ , we must first understand a phenomenon known in the audio world as “ masking ,” which occurs when two instruments share a similar frequency range . Since frequency is one of the ways in which the human brain tells different sounds apart from one another , masking will make it difficult to distinguish one instrument from the other and leaves the listener feeling like they can ’ t hear either instrument properly . When this happens in multiple frequency ranges simultaneously , it can give the impression of a cluttered mix that lacks definition between instruments . One of the best and easiest ways to combat this phenomenon is with complementary EQ .
By definition , complementary EQ is the use of opposite equalization curves on two or more different sources that work together ( i . e . complement each other ) to make both sources stand out in the mix . Usually , this will involve choosing a centre frequency that both sources share and then using the equalizers on their respective channels to attenuate that frequency on one and boost it on the other . On equalizers with a variable Q value , I recommend starting with something moderate since overly wide or narrow Q values will defeat the purpose of your cutting / boosting . Similar to the old saying about sculptors and statues , your goal is to start with a bunch of conflicting sounds and carve away everything that isn ’ t part of your spectacular mix .
The ideal tool for this is a fully parametric equalizer because it allows you to sweep the centre frequency in order to find the place that you want to attenuate / boost ; however , in a pinch , fixed-frequency and fixed-Q equalizers will still work . In fact , even the channel EQs found on most small , low-budget consoles will have enough flexibility for a basic implementation of this technique , so complementary EQ can even be used on small , simple systems .
Putting It into Practice The theory behind complementary EQ may sound difficult and technical to some , but it ’ s actually quite simple in practice . Let ’ s pretend we ’ re mixing a jazz-rock band with both an electric bass and a piano . When both instruments play low in their range , they will begin to mask each other because they both have similar low frequency content . To prevent this , we will determine where we want each instrument to sit in the overall mix , choose our centre frequency , and attenuate / boost according to our ears .
For example , we may choose a centre frequency of 80 Hz and decide to attenuate it by 6dB on the piano and boost it by 1.5dB on the bass . The more musicians there are on stage , the more likely it is that you will have to carve out a dedicated spot in the mix for each one .
The Speed Factor At the beginning of this column , I mentioned that using complementary EQ can be a life-saver in fast-paced situations . How ? There are a handful of masking issues that occur with surprising regularity , especially when dealing with low frequencies . The electric bass and piano example I used earlier is one of them , but I also regularly see issues with electric bass and kick drum . Sometimes electric guitar and electric bass can step on each other , as well as electric guitar and piano . At events like industry showcases where it ’ s unlikely that each act will get a comprehensive sound check before they hit the stage , complementary EQ can be set up in advance based on the band ’ s instrumentation to correct common problems before they happen . This means that when the band takes the stage and hits the first chord , every instrument will be heard in the mix . Of course , these settings will need to be refined and the levels will need to be re-balanced almost immediately , but right off the bat , each instrument will have its own spot frequency-wise . This has saved me from scrambling to correct a potential disaster more times than I can count .
Complementary EQ is a technique that every audio engineer should understand . It is relatively simple to implement , can be done on the most basic of systems , and is a great way to get a mix up and running quickly in high-pressure situations . While there are plenty of strategies for getting good live mixes , complementary EQ is an essential part of every technician ’ s toolkit .
60 • CANADIAN MUSICIAN