Buy PDF

E

It's always worth thinking about where you place EQ inrelation to other processors. It makes sense to performcorrective EQ before any compression, so that thecompressor isn't triggered by and doesn't boost anyunwanted frequencies. This means that if your sequencerhas a built–in channel EQ, you need to think whether it ismore appropriate to use an insert — or possibly both, asshown here.

Using high– and low–pass filters (top), you can 'bracket' thefrequency band you want to let through, cutting out unwantedfrequencies on either side — a helpful way of making spacefor other elements in a mix. High and low shelf filters level out('shelve'), so are a better option when you want to apply agentle boost to the top or bottom end.

There aren't really any hard and fast rules for EQ — you dowhat sounds best — but a useful guideline is to use narrownotches for 'surgical' removal of unwanted frequencies, butgentle, broad boosts when looking to augment one aspect ofa sound. You may be able to achieve more radical notches bycombining more than one filter.

Why are some analogue EQs, such as the Neve modelemulated below, so revered? It's because they do more thancut and boost frequencies: phase shifting and distortion also

Printer-friendly version

Published in SOS December 2008

What's The Frequency?A Guide To Effective EQTechnique : Processing

Manipulating the frequency spectrum is one of the most important skills in recordingand mixing. We explain the different types of EQ you can use in your mix and sharesome tips on how to get the best from them.Paul White, Matt Houghton

qualisation, more commonly abbreviated to 'EQ', is one ofthe key elements of the recording, mix or masteringengineer's toolkit, and you'll hear engineers talking at

great length about the sound characteristics of specific makesand models of EQ — such is the importance of EQ to a modernrecording. But simply knowing that engineer Bloggs uses aPultec on his kick drums teaches you very little about how andwhy he uses it. In this article, then, we'll take you through thedifferent types of EQ and explain their applications, as well asoffering tips and tricks about which frequency ranges you mightfind most useful for common instruments.

What Is EQ?

The term 'equalisation' comes from the pioneering days of thetelephone, when it described the process of correcting for — or'equalising' — tonal changes caused by losses in the longtelephone lines, but today the term is more generally used tocover all types of audio 'tone' controls. To put it very plainly, anequaliser is a frequency–selective filter that's able to cut or boostthe level of specified parts of the audio spectrum. The simplestequaliser consists of just one capacitor and one resistor. With theresistor in series and the capacitor linking the output to ground,you get a high–cut (alternatively, 'top–cut' or 'low–pass': they allmean the same thing) filter that's just like the tone control youfind on an electric guitar — that is to say, one that filters out thehigher frequencies. Putting the capacitor in series and theresistor to ground gives you a low–cut (or 'high–pass') filter, thatcuts out lower frequencies.

As long as no additional electrical load is applied to suchcircuits, the response is 6dB/octave (which means that the signallevel drops by 6dB for every octave below the filter's 'turnover'frequency), or 'first order'. These simple, passive circuits cannotbe used to boost frequencies, they can only cut them. To achievean EQ boost, you have to combine the filters with active circuitry,which is what Peter Baxandall did when he developed his bass and treble equaliser, which was capable of cutting andboosting both low and high frequencies using two independent controls. Baxandall's basic circuit still forms the basis of manymixing console high and low equaliser sections and is mimicked in the form of presets on a good number of EQ plug–ins.

The Highs & Lows

Let's look more closely at the simple first–order low–cut filter. AsI've just mentioned, the signal level drops by 6dB for everyoctave below the filter's turnover frequency, and this means thatany components two octaves down from that frequency will beattenuated by 12dB, those three octaves down will be attenuatedby 18dB, and so on. If you need a 'steeper' filter slope, you puttwo first–order filters in series, creating a second–order filter witha 12dB/octave response. Such filters are very useful forattenuating frequencies that are outside the area of wantedfrequencies, and they form the basis of the low–cut filters foundin microphones and mixers. However, although their responseshape is useful for cutting, wiring them into a boost circuit can beproblematic, because for every octave you go past the filter'scutoff point, the gain rises by 6dB (doubles in voltage), whichmakes it incredibly easy to run into clipping problems.

A more practical option for boosting a frequency region is the'shelving' equaliser. In these designs, instead of the gaincontinuing to change by 6dB per octave, the curve flattens out —or 'shelves' — so that you can adjust the gain of the desired highor low section of the audio spectrum by the same amount. Forexample, if you've a filter that's designed to affect onlyfrequencies below 100Hz, once the filter flattens, out all the lowfrequencies will be cut or boosted by the same amount when you

In this article:What Is EQ?The Highs & LowsWhat's In The Middle?Graphic EQMinimum Vs Linear

PhaseSome Practical

ConsiderationsThe EqualiserWhere To Cut & Boost

For CommonInstruments

Five EQ Tips

Home | Tablet Mag | Podcasts | WIN Prizes | Subscribe | Advertise | About SOS | Help Thu 3 Sep 2015 Search SOS Have an account? or Register for freeLog in

Sound On Sound : Est. 1985

Search News Articles Forum Video Subscribe Shop Readers' Adverts Information WebExtras

colour the sound. Linear–phase digital EQ is much moreprecise, but doesn't always sound as pleasing. Some plug–ins, such as the ddmf LP10 shown left, offer variable phasefor each filter, giving access to the best of both worlds.

turn the EQ gain control. Again, the more filters you stack inseries, the steeper the transition at the filter's operatingfrequency. (The screen shot at the bottom of this page shows ashelving equaliser plug–in.) Because the amount of gain levelsout, this type of filter is less likely to cause clipping problemswhen boosting. Most equalisers will use high– and low–passfilters only for cutting the extremes of the audio spectrum, andshelving filters where both cut and boost are desired.

What's In The Middle?

While the filters described so far are useful for general high–cut,low–cut and boost purposes, you'll often find frequenciesbetween these two extremes that need attention — such aswhen you need to reduce the boom of an acoustic guitar body,for example, or emphasise the crack of a snare drum — and thisis where the 'band–pass', or 'peak' equaliser comes into its own.This is essentially a tuned filter that offers both cut and boost,and operates on a specific band of frequencies. The range offrequencies that are affected is determined by the bandwidth of the filter (measured at its –3dB points). These adjustablefilters can usually be tuned over a wide frequency range, although the technical limitations of analogue circuitry mean thatanalogue band–pass EQs seldom cover the entire audio spectrum with a single filter. Digital equalisers, on the other hand,can have pretty much whatever range their designers decide they want to build into them.

The shape of the band-pass EQ curve is sometimes described as bell–like: the maximum cut or boost occurs at the centreof the bell and gets progressively less each side of it. The centre frequency of the filter divided by its bandwidth at the –3dBpoints gives the 'Q' of the filter, meaning that the higher the Q value, the narrower the filter response.

On smaller mixers (and some less sophisticated EQ units) with so–called 'swept–mid' controls, the bandwidth of the midfilter is preset — or may perhaps offer a couple of preset widths — but in a true 'parametric' equaliser the filter width isvariable, which means that the user is able to apply a broad boost, or to focus in on very narrow sections of the audiospectrum — or, of course, anything in between these two extremes. Parametric equalisers offer control over filter frequency,cut or boost amount (usually up to about 15dB) and bandwidth (or 'Q'), so there are three controls per band. Most practicalparametric equalisers have two or more bands that can be used at the same time to tackle problems in different parts of theaudio spectrum.

Graphic EQ

Graphic equalisers are based around a large number of fixed–frequency filters, either with fixed bandwidth or proportional Qresponses, usually spaced by a half, a third, or a whole octave,depending on the number of bands. Each band is controlledusing a vertical slider, which governs the cut or boost, with 'flat'being in the centre position — so clearly the name 'graphicequaliser' comes about because the faders show the generalshape of the EQ curve. Individual filter bandwidths are arrangedso that they overlap smoothly, while the highest and lowestfrequency sliders are usually linked to shelving filters to providemore useful control over the high and low extremes. Althoughthere's no reason not to use a graphic equaliser in the studio, most engineers prefer the parametric EQ because it gives themmore precise control. Live sound engineers also often like to use graphic equalisers, because they're fast to set up and quiteuseful for tackling general room EQ problems.

Minimum Vs Linear Phase

Analogue equalisers tend to colour the sound in a way that'smore complicated than simple frequency bosts and cuts,because they introduce phase shifts, some of which will be moremusically pleasing to the ear than others (one of the reasons thatpeople admire some particular 'classic outboard'). Unsurprisingly,digital equalisers are often designed to emulate suchcharacteristics, to the extent that both the frequency curves andattendant phase shifts are emulated as closely as possible. Thistype of EQ is a 'minimum–phase' design, but digital equaliserscan also be created with 'linear–phase' characteristics, where nophase shift is introduced between low and high frequencieswhen cutting or boosting — and this sort of EQ is ideal forcorrecting spectral balance issues without changing the soundexcessively.

It's probably true to say that the phase changes introduced by many classic equaliser designs make an importantcontribution to their sound, so it doesn't always make sense to choose the technically more precise linear–phase option. Youshould also bear in mind that linear–phase equalisers introduce quite a lot of delay, which means that they'll increase thelatency of your DAW by a significant amount. I like to think of traditional minimu-phase EQ as 'art' and linear-phase EQ as'science'. Put another way, analogue or minimu-phase EQs tend to be better for creative tonal shaping where you're lookingfor a musically pleasing sound, whereas linear–phase designs tend to be better for corrective, 'surgical' jobs, such as notchfiltering.

Analogue EQs tend to sound different for a number of reasons, not least the shape of the EQ curves — which may departfrom the theoretical curves we've discussed so far by intent, or perhaps by some accident of design. Then there's the qualityof the circuitry, as equalisation places heavy demands on both the headroom and bandwidth of the active support circuitry.Some vintage equalisers may distort in a musically pleasant way, while a badly designed one can run out of headroom whenlarge amounts of cut or boost are used, which can result in a harsh, unpleasant sound. Engineers creating digital models ofclassic analogue gear go to great lengths to emulate all the subtle distortions and quirks of the original, as it is often these thatgive it a unique sonic signature.

Some Practical Considerations

When using EQ, it's useful to understand something of the way our ears perceive the changes we make. In fact, you can trythis for yourself by playing a mix through the equaliser and then listening to the subjective results of narrow EQ cuts and

Universityof LawGDLDownload aProspectusfor more infoon our GDL

Universityof LawGDLDownload aProspectusfor more infoon our GDL

DAW Techniques100s of great SOS articles!CubaseDigital PerformerLiveLogicPro ToolsReaperReasonSonarStudio One

boosts at different parts of the frequency spectrum. What shouldbe evident right away is that narrow EQ boosts sound muchmore obvious — and unnatural — than correspondingly deep EQcuts. While EQ boost can be useful, it tends to sound mostnatural when the range of affected frequencies is fairly wide, andwhere the amount of boost used is quite modest. However,before you boost something you'd like to hear more of, tryinstead cutting those parts of the spectrum that you feel areoverpowering it: sometimes the effect of cutting a lower-frequency sound can make the higher frequencies seem brighter,even though you haven't EQ'd them at all.

You can also sometimes make instruments sit better in a mixby using low– and high–pass filters to 'bracket' the sound,removing unnecessary low and/or high frequencies — in fact, ifyou ever read our Mix Rescue articles you'll know just how usefulthis can be for de–cluttering a mix. The classic example is theacoustic guitar in the rock mix, which can sound much better witha lot of low end shaved off, because this prevents it fromconflicting with other sounds in the mix. The steeper the filter, themore assertive the bracketing — typically a filter–slope ofbetween 12dB/octave and 24dB/octave will do the trick. You can also afford to be fairly heavy–handed in this respect withinstruments such as electric guitar, which don't really have a 'natural' acoustic sound to get wrong. The same radical approachcan often be used for synths, where confining pads sounds into a narrower region of the audio spectrum can avoid conflictwith other instruments and thus really help to clean up a busy mix.

One pitfall you should avoid is EQing each sound in isolation to make it sound as big and shiny as possible. Although thismight make instruments sound good alone, the subjective sound of each part will change once the other elements of the mixare brought into play — and if you've tried to tune up each sound on its own, the chances are that your mix will soundsomewhat messy, as all the parts will probably be fighting to be at the front of the sound stage. In reality, some sounds, suchas vocals, need to be treated to sound very upfront, while other sounds can play more of a supporting role, and reallyshouldn't sound so big and glossy. If you listen carefully to some well–crafted commercial records and try to pick out thevarious different elements of the mix, this should be very obvious.

When it comes to recordings of acoustic instruments and voices, you should always try to get the best sound you can atsource, because many problems simply can't be fixed by EQ. What you may think of as a 'coloured' or 'boxy' tone that EQshould be able to fix may, in fact, be down to room reflections caused by insufficient damping in the recording area or byinappropriate mic placement — and where this is the case, you'll often find that EQing will make little or no improvement.

To find the parts of a sound that need equalising, the most common — and, indeed, the easiest — method is to use aparametric EQ with a Q setting of around 1, turn the boost right up, and then sweep the EQ across the frequency spectrum.Listen for those elements that benefit the sound and those that cause problems: the unpleasant elements should really jumpout at you when you sweep through them, giving you an idea of which part of the spectrum to cut. You can then experimentwith the depth and width of cut to get the best subjective result.

Some engineers may prefer to estimate the problem frequency before applying any such cut or boost, because this offersthe advantage that they haven't had their judgement clouded by the sound of a harsh EQ boost, but getting this right is, ofcourse, something that comes with experience and plenty of ear–training 'on the job'. Either way, remember what we saidabove: always make your final adjustments to a sound with the rest of the mix playing, because what sounds good in isolationdoesn't always sound good in context.

The Equaliser

Finally, then, a knowledge of EQ is important to today's music production process, and it can be used either to correctproblems or in a more creative manner, to shape sounds in a less natural — but musically satisfying — way. All these usesare valid, but whatever you do, don't fall into the trap of thinking that radical amounts of EQ will help you fix an imperfectsound at the mixing stage — because very often it won't! .

Where To Cut & Boost For Common InstrumentsThe English language is a wonderful tool in that it usually offers many alternative ways of describing similar things. Alas,that can also make it rather imprecise and confusing — particularly when it comes down to describing sound! We mightdescribe a sound as deep, warm, bright, shrill, crisp, forward, or perhaps shimmering. They're useful terms because we allknow roughly what they mean, but they're not a lot of use when you're trying to narrow down which frequencies to cut orboost.

In the main article, we describe how you can sweep a narrow–ish parametric EQ boost to zoom in on any problemfrequencies that you might want to 'notch out', and this approach can also be useful to train your ears, so that you getused to the different elements that make up the sound of different instruments. In time, you'll start to know intuitively whichareas to cut and boost to get the sound you want. Until then, here's a mini reference guide. The list below isn't exhaustive,but it provides some useful starting points for commonly used instruments — and as you can see, the same term canmean different things for different instruments. One word of warning: as always, these are only guidelines, and you reallyhave to listen and experiment if you want to get things working in the context of your track.

Kick Drum: Bottom or depth is usually found in the 60–80Hz region; slap at 2.5kHz.

Snare Drum: Weight, fatness or body at about 240Hz; bite at 2kHz; crispness at 4–8kHz.

Hi–hat: 'Gong' at 200Hz; shimmer at 7.5–12kHz.

Cymbals: 'Clunk' from 100–300Hz; ringing overtones at 1–6kHz; sizzle at 8–12kHz.

Rack Toms: Fullness around 240Hz; attack at 5kHz.

Floor Toms: Fullness around 80–120Hz; attack at 5kHz.

Congas: Resonance around 200–240Hz; slap at 5kHz.

Bass Guitar: Bottom at 60–80Hz; attack or 'pluck' at 700Hz to 1kHz; 'pop' at 2.5kHz.

Electric Guitar: Mains hum at 50Hz (UK) or 60Hz (US); fullness at 240Hz; bite at 2.5kHz

Acoustic Guitar: Bottom or weight at 80–100Hz; body around 240Hz; clarity from 2–2.5kHz.

Hammond/Electric Organ: Bottom from 80–120Hz; presence at 2.5kHz.

Acoustic Piano: Bottom from 80–120Hz; presence between 2.5 and 5kHz; attack around 10kHz; 'shrillness' at 5–7.5kHz.

Horns: Fullness at 120–240Hz; shrillness from 5–7kHz.

Email: Contact SOSTelephone: +44 (0)1954 789888Fax: +44 (0)1954 789895

Registered Office: Media House, Trafalgar Way, Bar Hill,Cambridge, CB23 8SQ, United Kingdom.

Sound On Sound Ltd is registered in England and Wales.Company number: 3015516 VAT number: GB 638 5307 26

Current MagazineWeb EditionTablet Mag appBuy PDF articlesMagazine Feedback

SubscribeSubscribe NowWeb Subscription FAQs

Podcasts

Competitions

Home

SOS Shop

News

SearchNew SearchForum SearchSearch Tips

ArticlesReviewsTechniqueSound AdvicePeopleGlossary

Help + Support

ForumToday's Hot TopicsForum Channel ListForum SearchMy Forum HomeMy Forum SettingsMy Private MessagesForum Rules & Etiquette

VideoWatch exhibition videos, tutorials,interviews, masterclasses

Readers ClassifiedsSubmit New AdvertsView My Adverts

My SOSChange PasswordChange My EmailChange My AddressMy SubscriptionMy eNewslettersMy Downloads

InformationAdvertisingMagazine On-sale DatesAbout SOSContact SOS StaffControlled CirculationLicensing EnquiriesSOS Logos & GraphicsSOS Site AnalyticsPrivacy Policy

Home | Search | News | Current Issue | Tablet Mag | Articles | Forum | Blog | Subscribe | Shop | Readers AdsAdvertise | Information | Privacy Policy | Support | Login Help

We accept the following payment methods in our web Shop:

All contents copyright © SOS Publications Group and/or its licensors, 1985-2015. All rights reserved.The contents of this article are subject to worldwide copyright protection and reproduction in whole or part, whether mechanical or electronic, is expressly forbidden without the prior written consent of the

Publishers. Great care has been taken to ensure accuracy in the preparation of this article but neither Sound On Sound Limited nor the publishers can be held responsible for its contents.The views expressed are those of the contributors and not necessarily those of the publishers.

Web site designed & maintained by PB Associates | SOS | Relative Media

Published in SOS December 2008

Brass: Warmth at 200–400Hz; 'honk' at 1–3.5kHz; 'rasp' at 6–8kHz; shrillness at 8–12kHz.

Solo Trumpet & Sax: Warmth at 200–400Hz; nasal tones at 1–3kHz.

Strings: Fullness at 200–300Hz; 'scratch' (bow and string noise) from 7.5–10kHz.

Vocals: Fullness around 120Hz; 'boom' around 200–240Hz; presence at 5kHz; sibilance from 7.5–10kHz. Matt Houghton

Five EQ Tips1. You can't boost what isn't there, so get things right at source. Boosting the top end will only result in undesirable crackleand noise if there's little there to augment.

2. You should always EQ in the context of a mix because that's where things need to sound good — no–one else is goingto be listening for the perfect hi–hat in isolation!

3. Too much bass or sub–bass will eat up your mix headroom, which makes high–pass filters your best friend.

4. Narrow notches and broad boosts usually work best: so if you hear can hear a nasty resonance, try a narrow cut with alinear–phase EQ; and if you're looking for tonal change, work with gentle, broad boosts and cuts using an analogue EQ (oranalogue–modelling plug–in).

5. Different analogue–style EQs impart different characteristics, so try to experiment with different hardware or plug–inEQs to get the results you want. Matt Houghton