Tuesday, March 13, 2012

EQ - What To Do First

 As a sound guy one of the most powerful tools you have at your disposal is the EQ.  I'm not going to cover any tricks about specific instruments in this post but there's a link to a great article that does at the end of this post.  What I want to talk about today is what each type of EQ is best used for.

Starting with the one that is most misused let's go to the console.  That's right, those knobs on each channel strip that are roughly equivalent to the bass and treble on your stereo.  Some consoles are acually that simple, some have four band fully parametric setups that can be pretty intimidating.  We'll save parametrics for a little later. Channel EQ is to modify the signal of an individual instrument or voice as it passes through the mixer.  But STOP RIGHT THERE!!! (!)

This is so important I'm going to start a new paragraph to rant about it.  Before you even touch that channel EQ, if you need a different sound out of a mic on stage or in the live room of a studio, you need to move the mic, or try a different mic.  A good sound guy will have an encyclopedic knowledge of how different mics sound and how they sound when used in different positions and combinations.  A lot of this comes from experimentation and the rest comes from swapping stories and reading articles.  Trust me on this though, your signal will be so much cleaner if you use the right mic in the right position than if you're lazy and just "fix it in the mix".

So once you've got your mics chosen and placed you dial up your gain structure and start tweaking EQ.  Think of the channel EQ as the tool you want to use for the artistic part of your craft (the scientific part comes later in the signal chain).  Also, use boost only when you absolutely have to.  If something sounds muddy, turn down the lows before you boost the highs.  You'll prevent feedback, ear fatigue and have a better shot at building a coherent mix if you mostly subtract.  I don't say only subtract because this is one of those rules that's hard and fast... until it's not.  It's OK to boost so don't be afraid to, just make it a careful decision when you do.

So let's say you've got four or five vocal channels open and they all need 200 Hz and 1.5 kHz cut to add clarity and eliminate feedback.  If you do that for all five mics on the channels, you're done, you can't make any artistic decisions about that signal unless you're on a big desk with a ton of channel EQ.  So where do you go to get the job done?

Two places.  The first would be to go to the FOH graphic EQ and start notching out problem frequencies.  If you're on a good system that's been well tuned by a thoughtful engineer, then frequencies that tend to feed back in that space have probably already been notched out.  Often in bigger systems this is done in the digital loudspeaker management box, that's what the guys are doing with the laptops and the pink noise. That leaves the graphs flat for the FOH engineer to touch things up for each particular event. But what if your notches help out the vocals but hurt the drums and guitars?

Grouping all the related channels together allows you to insert a graph on just those signals.  Just one channel of graphic EQ (or two if you're mixing stereo) can take care of all the issues with that group of inputs (the science) leaving your channel EQ free to delicately shape the sound (the art).  Need to take care of another group in a different way?  Just insert another graph and off you go.
This is the area where a stand alone parametric EQ can come in very handy.  A parametric just means that you have full control over every parameter of the filter.  A basic EQ is at a fixed frequency and you can run that frequency up and down.  A swept EQ lets you choose what that frequency is, and a fully parametric EQ also lets you adjust the Q or the width of the filter, from razor sharp to octaves wide.  Parametrics tend to have fewer bands because you need more control for each band.  A 31 band graph can easily fit in a single rack space if it uses short throw faders for each frequency.  Some parametrics cover just two or three bands and take up two or more rack spaces.  In the digital realm, the engineer often has a fully parametric four band on each channel, and the same on each output, with the option to also switch to or add in a 31 band graphic.  
That's some serious power!  But you have to know how to use it.

Keeping the purpose of each type of EQ in mind when you build a system, or plan to expand one, or mix on some one else's will always give you the best results possible for a given situation.  A lot of times you don't have all the right tools at your disposal and you have to fake it or make do.  But whatever the situation, a well educated sound guy is always in a position to make the best of it.
For a little additional reading along the same lines check out THIS ARTICLE at ProSoundWeb, written more for a recording audience than live sound but all the same principles apply.

Also, I've been posting links to articles on my Facebook account but my non-audio friends are getting tired of them.  To have posts show up in your news feed, like the SNR page on FB.  There's a link just under the email subscription box at the upper right. 

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