The Gentle Art Of EQ
This month's Masterclass looks at the way equalisation can be used to creatively enhance your music.
Equalisation is often misunderstood and misapplied but, used properly, it is one of the most powerful audio processors at our disposal. Paul White explains how to mind your Es and Qs.
Equalisation is just a fancy word for tone control and, no matter how complicated the equaliser, it helps keep things in perspective if we bear that simple fact in mind. All an equaliser does is cut or boost the level of some part of the audio spectrum. Of course, technology has brought us a long way since that innocent single knob labelled 'tone', and today's equalisers can be used in a great many creative and corrective situations. But before getting in too deep with equalisers, we should really look at the audio spectrum to find out what that's all about.
According to the textbooks, the human hearing range extends from around 50Hz to 20kHz, though those very same books will also point out that few individuals, other than young children, can hear pitches anything like as high as 20kHz. A more realistic figure might be 15kHz for a teenager and somewhere around 12kHz for people in their 30s and 40s. After that it's downhill all the way. What I find really puzzling though, and this is scope enough for an article in its own right, is that even when your measured hearing response starts to fall off at 12kHz, which mine does, it is still very easy to hear the effect of equalisation much further up the spectrum or of filters that artificially restrict the audio bandwidth. This is further corroborated by studio engineers who claim to be able to differentiate between two identical circuits, where one has been modified to handle frequencies up to 50kHz and one handles frequencies up to 30kHz. In theory, both limits are well above the limit of human perception, so it seems that what we don't hear has a way of affecting what we do hear.
A similar perceived result can be heard when comparing a good capacitor mic with an audio bandwidth in excess of 20kHz with a typical dynamic microphone which is nominally flat up to 15kHz or so. Providing both have reasonably flat responses below their cutoff point, they should both sound much the same to someone who is, in effect, deaf to all frequencies above 12kHz, but in practice, the high-frequency detail captured by the capacitor microphone lends the capacitor an entirely different character to the dynamic mic.
Probably the best way to look at the audio spectrum is to check out some common musical sounds and see what part of the audible range they occupy. The low-frequency limit is usually quite easy to define — as an instrument can't produce a pitch below the fundamental frequency of its lowest note — but the high-frequency end is somewhat less well-defined. That's because nearly all sounds include harmonics that extend right to the top end of the audio spectrum and beyond, even though the level of these harmonics is probably very low. All we can do is pick a ball-park range to show where most of the audio energy from a particular source resides and ignore what falls above it. For example, a flute produces a relatively pure tone, though the breath-noise harmonics extend right up across the entire audio spectrum. Figure 1 shows a few common sounds in chart form so that their frequency ranges can be compared.
Starting right at the bottom of the spectrum with bass sounds, the bass drum puts out most of its energy in a narrow band between 50Hz and 150Hz — depending on how it is tuned — but the attack transients reach right up into the upper mid-range. This can be confirmed by applying some EQ boost to a bass drum sound at around 4-6kHz; the difference in the attack characteristic is very noticeable.
The lowest note on the electric bass guitar is 41 Hz but the higher notes contain significant energy right up to 2 or 3kHz. Likewise, the traditional pipe organ goes an octave lower — down to 20Hz, where sounds are felt rather than heard — while the high notes are putting out significant energy up at 8kHz and beyond.
The electric guitar has a starting point one octave higher than the bass guitar at 82Hz and, because of the restricted range of electric guitar speakers, there's little energy above 4kHz. Even so, it's a mistake to draw too many conclusions from the upper limit of any sound, because EQ applied above this arbitrary limit will almost certainly have some audible effect.
Moving a little higher up the spectrum, we find that vocals can range from around 80Hz to 1kHz, depending on the style and sex of the performer. Again, there's a significant amount of energy above that range, which is why live mic manufacturers often build in a presence peak at 3 or 4kHz, and de-essers have to function at between 5 and 10kHz to remove sibilance. Brass instruments also tend to occupy the mid-range of the spectrum, typically 80Hz to 1 kHz — unless you count the tuba, in which case you can add almost an octave to the bottom of that figure.
Few instruments produce any significant amount of energy at the high end of the spectrum, the piccolo and xylophone coming closest in the 600Hz to 5kHz range. The upper harmonics of cymbals, bell-trees, triangles and suchlike extend well beyond the limit of human hearing. Sampled and synthesised sounds haven't been included, because they can cover whatever range the electrical circuitry is capable of supporting which, in theory, can be the entire audio spectrum.
Having taken a brief look at the audio spectrum and some of the instruments that occupy it, now would be an appropriate time to get back to the subject of equalisation.
In a perfect world with perfect microphones and perfect tape recorders, do we ever need to equalise sounds? There are those who say not, and they present very good arguments for their case, but in the real world of pop recording, where the emphasis is on appropriate rather than accurate sounds, equalisation has become a way of life. After all, when was the last time you heard a pop record with a drum sound that bore any resemblance to an acoustic drum kit? It stands to reason — we mic drum kits from a couple of inches away, which isn't a normal listening position, so it's not surprising that we have to EQ the sounds quite drastically to get something that actually sounds good.
This miking technique was originally devised to cut down on spill from other instruments, but the sound it produced (with a few tweaks of the EQ) was so distinctive that it rapidly became the norm for pop records and the actual acoustic sound of the kit was largely forgotten.
In the case of the electric guitar, circumstance also dictated sound. During the pioneering days of electronics, amplifiers were pretty crude and tended to distort drastically at high volume levels. Likewise, speaker design wasn't really up to handling much power, and the brute-force 12" models that became so popular couldn't reproduce any of the higher harmonics from guitar pickups. If modern technology had been available from the outset, electric guitars might have all sounded perfectly clean and as bright as an acoustic, but as it turned out, the combination of limited-bandwidth speakers and excessive amounts of distortion led to the rock sound that we all know and love. Furthermore, now that low distortion, high bandwidth sound processors are available, it's ironic that their designers are all trying to write algorithms that successfully duplicate the sound of those wonderful, old, low-tech guitar amplifiers. The reason for this slightly roundabout little diatribe is to attempt to justify the use of equalisation as a creative process rather than simply as a means of solving problems created elsewhere in the recording chain.
EQ can be used creatively in many ways, but one of the most popular applications is to separate two sounds within a mix that threaten to overlap and fill the same part of the audio spectrum. Some overlap is inevitable, but if, say two electric guitars or a brass sample and string sample are fighting for the same space in a mix, EQ can often be used to reshape the sounds, forcing them into slightly different areas of the spectrum. For example, a peaking equaliser can be used to add a degree of bite to one sound at one frequency while the other sound can be peaked up at a different frequency. Similarly, the top or bottom end of a sound can be trimmed to avoid conflict, a typical example being the acoustic rhythm guitar in a pop mix, where it is common practice to filter out the bottom end quite drastically. This leaves a bright sound that sits well in the mix but without the bassy, boxy element that might conflict with the other midrange instruments or the vocals. At this point, it is valuable to examine a few common instruments to see how EQ can be used most effectively.
During the 60s, the bass guitar was used to provide little more than a low-frequency pulse; its sound was invariably dull by comparison with today's bass sounds. The turning point was probably marked by The Who's John Entwhistle, who used a much more powerful, aggressive tone, bringing the instrument into the limelight. The contemporary bass guitar sound is a result of changing from tape-wound to wire-wound strings, of new playing styles, and of the degree of equalisation that can be applied using a contemporary bass guitar amplification system. Whether the bass guitar is DI'd or miked during recording, the equalisation on a typical console can be used to create a wide range of tonal characters. (I'm assuming the use of console with four-band EQ and two sweep mids, but it is possible to use an external graphic or parametric equaliser to achieve the same result.) Boosting at around 80Hz can be used to pull out the low bass, while boosting between 500Hz and 800Hz adds a nicely aggressive bite. Boosting higher up the spectrum tends to bring out the finger noise and little else, so if a bright sound is what you're after, get it as close as you can at source. Playing technique has a lot to do with the tone of a bass guitar and no amount of EQ will compensate for a weedy finger-style of playing. A touch of low-mid cut at around 200-250Hz can sometimes be effective in combination with a little low-end boost; this warms up the low bass end without allowing the low-mid area to get uncontrollably boomy.
Bass synths can be treated in much the same way, though their ability to produce higher harmonics means that EQ at higher frequencies will also be effective. However, be cautious when using very bright bass synth sounds; they can so easily fill up all the space in a mix, leaving the whole thing sounding congested.
If you need to add warmth to the sound of an electric guitar, concentrate on the area between 125Hz and 200Hz. There's no point adding boost much below this region, as the lowest note's fundamental frequency is 82Hz. Bass boost will only bring up the cabinet boom and make the overall sound muddy; it could also conflict with the bass guitar. Equally important, boosting the bass end will accentuate any mains hum in the signal — most guitar pickups, especially single-coil jobs, pick up a surprising amount of hum.
To add attack to the sound, go for the 3-4kHz section of the spectrum, but don't add any really high-end boost unless the guitar is DI'd, as there's not much coming out of a guitar speaker above 3 or 4kHz. All you'll do is bring up the background noise and, if the guitar is being used with an overdrive sound, this will tend to go buzzy or fizzy.
In a congested mix, two similar-sounding electric guitars can be separated by adding bite at different frequencies, say one guitar at 3kHz and one at 4kHz. However, this is rarely as successful as getting a different sound at source. If you can use two different amplifiers or preamp settings while recording the two parts it will help. It also makes sense to use different types of guitar — say one with single-coil pickups and one with humbuckers. If you're miking the guitar amp, try using different mics for the different parts — a dynamic for one take and a capacitor for the other will make a noticeable difference, even if the guitar, amp and player remain the same.
I try to record acoustic guitars with little or no EQ, preferring to move the mics in order to get the right basic tone. But players and producers always seem to want to add more top end, so some EQ is inevitable. More severe EQ may be called for if the acoustic guitar is playing rhythm in a pop mix, because the bass end can clash with the other instruments in the arrangement. To thin the sound out a little, try some cut around 200Hz or shelve off the bass using the low equaliser control. Boosting in the region of 4 to 6kHz adds a nice American jangle, but you need a good guitar with fresh strings to really make this work and even then, some engineers use an exciter to help things along. You also need to use a good-quality capacitor microphone, as dynamic mics are insufficiently sensitive and fail to reproduce the high-frequency detail which characterises a good acoustic guitar sound.
When recording vocals, always use a pop shield, as no amount of EQ will fix popping once it's on tape. Try to get as near as possible to the sound you want, without resorting to equalisation, by selecting the most sympathetic microphone. General brightening can be achieved using the shelving high EQ control on the mixer, but keep a wary ear open for sibilance. Boosting lower down, at 1-2kHz, gives a rather honky, cheap sound to the vocals and so is not recommended other than as a special effect. Presence can be added by adding just a little boost at 3-4kHz using the upper mid sweep equaliser, but be sparing in this as the natural character of the voice can easily be lost. In a mix of backing vocals, rolling off a touch of bass often helps the sound fit in better with the mix.
As intimated, drums are a special case when it comes to equalisation, because the accepted pop and rock drum sound is not that of a natural kit. The trick is to make the drums sound both bright and solid but not too 'thick'.
A close-miked bass drum without EQ will often sound unusably bad, though you may strike it lucky. Most often there is a need to add definition to the hit, plus a degree of low-frequency weight. For a straightforward, punchy sound, a little boost at 80Hz will almost always improve matters, but to get a deeper sound without the end result being either boomy or too stodgy, try adding 10dB or so of boost with your shelving bass control (most consoles have their bass controls at 50 or 60Hz) and then wind in 10dB or so of cut at around 220Hz using the lower mid control. The two controls work together to produce a narrow area of low-frequency boost rather than the rather wide, uncontrollable boost that is obtained by using the low EQ on its own.
To add definition to the beater impact, boost the upper mid range between 3.5 and 6kHz, choosing the final setting by ear. A wooden beater is far better than a felt one for producing a modern kick drum sound, and the slap can be further enhanced by taping a piece of thin plastic on the drum head at exactly the spot where the beater impacts. Credit cards work splendidly for this job!
Toms may be handled in much the same way as bass drums, with boost (using the lower mid sweep control) in the 80 to 120Hz region, the exact setting depending on the size and type of tom. Careful adjustment of the upper mid control can help pick out the stick impact, and if the tom rings on too much or if it rings in sympathy with other drums, you can usually afford to roll off quite a lot of bass without the result sounding thin in the context of a mix. I often use a Drawmer gate's side-chain filter for this because of its very sharp response — I know that isn't what it was intended for, but it does the job perfectly! This kind of corrective EQ is invariably better than applying too much damping to the drum.
Snare drums are quite unpredictable and you never quite know how they're going to sound until you've put up a mic and listened to the result over the monitors. The sound can be fattened by boosting the 90-140Hz band, while the bite can usually be located in the 3-7kHz region. It's easiest, when searching for the right area, to apply full boost then tune for the appropriate pitch. Once you've found it, you can back off the degree of boost until you have a sound you can live with. If the drum still doesn't sound crisp enough, consider switching to a capacitor mic or patching in an exciter.
Always record cymbals at a low level to prevent tape overload and keep in mind that they always cut through more loudly than you expect. Brightness can be added using the shelving high EQ control or you can tune the upper mid control until you find a sweet spot. In general, cymbals are recorded as part of the overhead mic mix, and in some cases, it can help to roll off the bass end quite significantly to prevent the drum sounds picked up by the overheads from obstructing the drum sounds from the close mics.
Brass and string instruments work on entirely different principles but they do respond to equalisation in similar ways. Between 1kHz and 3.5kHz the sound can become nasal or honky, which means a little subtle cutting in this region can sweeten things up. To add high-end sizzle, move up to the 6-10kHz band and try a little boost there, but don't overdo it or the sound will become 'spitty'. For a warm pad sound from string or brass samples and synth patches, roll off a little top and add a hint of boost between 300 and 400Hz.
To record a real piano you'll need good mics — ideally two of them. The bass can be enhanced by boosting at 90-150Hz, while the attack detail can be brought out by bringing up the 4-6kHz area of the spectrum. If the sound is boomy, look for the offending area between 250 and 350Hz and apply just enough cut to keep it under control. Because the piano is such a natural instrument, it pays to use less EQ and concentrate instead on putting suitable mics in the right place. Electronic pianos can be equalised in the same way, though many models offer such a range of piano sounds that equalisation may be quite unnecessary.
Equalisation should always be brought into play after you've done your best to get the right sound at source. Excessive equalisation makes an instrument sound unnatural, and while this may occasionally be what you want, you should first know how to make things sound convincing.
It is important to understand that the human ear is far less critical of EQ cut than it is of boost, so if you can, solve the problem by cutting the area of the spectrum that seems to be too loud rather than boosting the weak area; the result will be more natural. Often a combination of cut and boost is required, but always use the bypass switch to flip back and forth between the equalised and unequalised sounds, to make sure you really have improved matters. Equally, when you have EQ'd an instrument in isolation, make sure that the setting you have chosen works in context with the rest of the mix, as parts often sound quite different once everything else is playing.
Be aware that different equalisers produce a different subjective effect (even though their specifications may be similar), and if you just need to generally brighten a sound or add a little warmth, your high and low shelving equalisers will probably do a smoother job than your mid-range sweep equalisers. Professional engineers tend to have certain favourite outboard equalisers, and it is now suspected that their phase characteristics may be as much to do with their subjective sound as their EQ cut and boost capabilities.
While you may be able to use one of these esoteric devices to apply quite radical EQ treatment to a sound and still get a smooth, natural result, the equalisers found in mid and low-priced consoles are generally less forgiving. If you strive to get your sounds right at the outset, then EQ is an invaluable ally in shaping those sounds to your liking, — but don't fall into the trap of accepting second best and then hoping to fix it in the mix.