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Equalization: A basic overview

equalization.jpg

adapted from http://www.kubton.com/eq.html

I have read comments that compression is the most misunderstood audio process but I really think it is equalization. It might be the most over and under used audio processing tool at the same time. What complicates the matter is factors intrinsic to our humanity. We perceive different frequencies different ways. Some frequencies will sound louder or quieter than their actual volume. This is why some audio hardware has a “loudness” button. Most people will try to improve sounds by boosting frequencies. But EQ is a sculpting process. The best result will be attained by boosting and cutting. You can accentuate one frequency by reducing another frequency , and it not make the sound muddy. Following is a basic overview of the spectrum of audible frequencies.

20-40hz: Edge of human range of unwanted rumble often complete removed.
40-80hz: Sub-bass or “feel” of bass. Can add low end kick or over power mix. Is not produced by small speakers..
80-250hz: Bass 100-200hz can be boosted to add fullness or cut to reduce boomy sounds.
250-600hz: Fullness or some vocals and percussion. The cardboard box sound of kick drum is around 300-400hz.
600-4khz: Midrange all too easy to add mud. 800hz is where the “cheap” sound comes from. 2k-4khz is where the attack of most percussion and some other instruments reside.
4-6khz: The “presence” range that determines how far out in front of the mix vocals sound. Can easily become grating.
7khz: The nasty realm of sibilance, the unwanted “s” hiss
8-20khz: This is the range of “air” or “brilliance”, and its presence adds sparkle.

In addition to the tips and guidelines in this article the Interactive Frequency chart is a handy reference guide for spefic instruments. It shows the breakdown what part of that instrument resides where in the spectrum. But there is a lot more EQ than knowing where the instruments sit in the spectrum.

Monitors
The ideal audio monitor will have a flat response curve across the whole spectrum so it is as transparent as possible. But there is no replacement for listening on different sound systems. Listen in a car, on a cheap CD player, on your home stereo, and anywhere else you can think to listen to it. This will give you valuable perspective that will help you improve your mixing, especially for getting the tricky low end right. Low sounds are harder to hear at low volumes. This is why a spectrum analyzer can be a useful tool to see what makes up a sound.

Below is a list of guidelines of what frequency does what. And they are just that… guidelines. I used several sources and personal experience and experimentation to compile them. There are no hard and fast rules when it comes EQ. Sometimes I think professorial sound engineers do a disservice to amateurs and hobbyists by declaring what should be boosted and cut; it really depends on the source material and the entire mix. Also, pros benefit from skilled arrangements, professional musicians and vocalists, and quality gear throughout the entire signal chain. A lot of EQ advice is intend to get a “professional sound” which generally means sounding like everything else on the radio. That is fine but I would strongly suggest that you try and achieve the sound you want. Remember: equalization is not a magic bullet. If the sound is bad to start with, EQ is not going to fix it. You cannot boost what is not there.

The Low Down

20hz is the very low end of human hearing. 20-40hz is out of instrument range. This is the rumble of an earthquake, thunder of anything else earth shaking. Usually nothing desirable can come from a boost in this range. It sometimes can cause problems. Ambient sound like that of train or freeway or things moving in the room can rumble its way into ruining your mix. It is often completely filtered out. A lot of sound systems don’t even go this low.

Here Comes the Bass

40hz to 80hz or the 1st octave is the sub-bass of the “feel” of the bass. Its an important range for hip-hop, dance or electronic music. If you want to rattle an impala at a stop light or send thunderous pulse through the planks of a dance floor this range is for you. Bass is also hard to work with. These frequencies are made for sub woofers or large speakers. Small sound systems and even monitors frequency response rolls off in this region. This is compounded by psychics. Low end frequencies are not heard as well by human ears at low volumes. You often hear that you should try and listen on different and varying sound systems which is absolutely true but you should also listen at different volumes. while true of all sounds varied listening is critical in this range. Despite monitor’s transparency they can under emphasize bass especially small monitors. Due to the physics small speakers have trouble replicating low frequencies. This is the reason for bass boost on small systems and headphone products. The danger here is boosting the bass to overcompensate for poor bass response or listening at low volume levels only to find it overwhelms the mix at high volumes or on systems large speakers and sub woofers that produce more bass. It usually is enough to boost just the baseline or bass drum or both to get some nice tight powerful bass. Boosting to many tracks in this area can easily over power the everything else. Often all other instrument these in this range are completely filtered out.

Boom, Boom, Boom

100hz has the boom. Often guitars or other instruments will sound boomy and a cut at 100hz will remove that quality. at 100hz bass and guitar tend to blur together cutting the guitar here helps separate the two. A boost at 100hz can also add fullness to a thin sound.

200hz-250hz can add fullness to vocals but also muddy things up quickly. It is a good place to start look for mud in vocals. Small reduction or boosts can be help but changes in this range can become dramatic quickly. Mud and fullness of other acoustic instruments hang out around here also. Slight boosts to fill out a thin sounding acoustic guitar is common in this range. Also this is the range the fullness of a snare and gong sound of cymbals usually reside. 250hz-600hz is the borderlands between midrange and bass. Some fullness for vocals can be found hear also. If your kick drum or other low register percussion has that icky cardboard box sound a cut some around 300hz to 400hz can get rid of it. this same range is also a good place to get space between the baseline and bass drum.

Middle of the Road

600hz-4khz is the midrange. This is tricky area. Subtlety is the key for it is easy to get unintended result. In this range it is easy to induce ear fatigue. It is also the range in which edgey and aggressive sounds come from but it is an extremely fine line even if you are making aggressive music. You can think of it as the telephone band. If you create a step bell curve over these frequencies cut almost all the frequencies on either side and greatly boost most the ones inside of the bell and you get the telephone sound. The sound referred to by a host of negative terms like cheap, plastic, tinny, toy sounding, unmusical, that is almost universally loathed is prevalent around 800hz. 800hz is the area where that can boost or reduce the punchiness of a base guitar but is most often reduced to remove that cheap sound in other instruments.

Climbing above 800hz between 2khz-4khz is the area of the attack of the beater hitting a percussion instrument and the attack of some other instruments can be accentuated or diminished here. Sound can really mush together in this range so it can take so work to get everything to fit.

Stage Presence

4khz-6khz is usually the frequency people are talking about when the word presence is used. The presence knob on a guitar amp boosts these frequencies. These frequencies affect how close the sound seems and can help separates it form the rest of the mix. It is the range that can make vocals or instrument solos seem “up front.” It is also easy to abuse. To much boost can easily become grating and listening fatigue will almost assuredly be induced.

Sssssssssssss!

7khz is the sibilance or “s” sound area of the frequency spectrum. This where you can reduce the unpleasant and sometimes overpowering “s” sounds known as de-essing. It can work wonders but if over applied can take the life out of the vocal track.

Way Up High

7k-8k is where the brightness of cymbals and other high register percussion is. It is often referred to shimmer or sizzle. It can all add some bite to other instruments. Sometimes boosting in this area can yield a metallic sound.

8k and above is often referred to as air, brilliance, breath sound, or sparkle. These "air" frequencies are where that unpleasant sound often referred to as the ice pick sound or brittleness can be dealt or a sound brightened up and sparkle added. 10k is a good starting point to look at adding some brilliance. 15k and above is more the area referred as “air.”

Some General Tips:

Types of eq vary greatly(it would take an article just as long to explain them all.) the best eq hardware or software is one that you like the sound of and you have a good understanding of and find easy to use.

A lot of the time use eq is addition by subtraction.

A spectrum analyzer is a good tool can be useful and is a great learning tool to see what makes up what sounds.

It helps to think of the frequency spectrum in 3 dimensional terms.

Remember there is a ying-yang quality to there frequency spectrum. A boost will diminish something else etc. And don’t forget panning. Eq and panning go hand and hand to help everything sit in the mix

Listen to your sounds on as many different systems as possible at different volumes.

Do not rely on numbers use your ears. Experiment: nothing is set in stone.

Mix in shorter focused sessions and don’t burn your ears out.

Search out more info on the web. Like GI Joe says, "Knowing is half the battle."

Have fun.

 

Here are some free eq plugins to help you with your tone shaping needs. This actually is a pretty thin area when it comes to free plugins. I suppose eq is not the sexiest piece of digital kit and most host come with decent eq it as not as attract to develop. I wish a few virtual analog snyths would be replaced by eq’s. Oh, well. This is good stuff but if oddly enough there is not a lot choice when comes to free plugins emulating the vintage hardware eq units. You’ll have to pay for the good ones like that.

  • Nyquisteq is great eq plugin from Magnus at Smartelectronix. the name comes from being able to handle sound up to the Nyquist Frequency without the normal problems. it handles the low end well also and and gui is uncluttered which makes all 5 bands easy to use. it is the most transparent of the eq listed here.
  • Kjaerhus Classic Eq has a nice emulation of classic analog sound. it is not great when precision is need but it is great for general eq tasks. Being in stereo lets you create some cool panning effects by splitting frequencies right and left. it look and acts like a graphic eq unit you might find on a lot of consumer audio equipment so it should be easy to use and comfortable to most users.
  • The Pariseq may not be that attractive but it sounds good and is easy to use. Unfortunately its developer’s site is gone. But you can still download it here. This eq is well suited to being an "effect" as well a more typical use for an eq.
  • Electri-Q great all around eq.
  • Voc-EQ pro as is names implies is a useful tool for vocals.
  • Voxengo span is a real time spectrum analyzer plugin. It can help you see whats going on with your sound. a useful tool in tandem with eq.
  • Overtone is another free equalization plugin from voxengo. This again is made to really color the sound in a good way. it has a few more bell and whistle than the others.
  • KarmaFx Equalizer is a 31 band graphic eq that you might like. It has some nice options to give you a lot of control while maintaining a a simple layout.
  • TDAe EQ2008S is a graphic style sith eight bands stereo(8 bands each side)EQ.