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3D Mixing Part 3: Equalization

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This post is part of a series called 3D Mixing.
3D Mixing Part 2: Panorama
3D Mixing Part 4: Compression

One of the most important tools in mixing is the equalizer. It shapes individual sounds, bus groups and mixes into cohesive wholes. If used correctly it can add clarity to muddy sounds or sparkle and definition to already great sounds. In this portion of our ongoing series, we will take an in-depth look at some EQ tips, frequency concepts and a few instrument specific techniques to help you create cleaner sounds and mixes.


Why EQ?

The purpose of EQing is to create clearer and larger sounds that are well defined and inhabit their own specific space within the frequency spectrum. This is achieved in different ways depending on program material, but the method by which it is achieved is largely systematic. What is needed more than anything in the process of EQing a good sound or mix is an easily learned process and a lot of experimentation and detailed listening.


Fundamentals

Theoretically, humans perceive waves as sound if they inhabit a range from 20 -20k cycles per second (Hz). In reality, this number is closer to 35-18k cycles with the bottom extreme being felt more than heard and the upper being barely audible. Within this spectrum, different instruments and sounds inhabit different frequency ranges that are specific to their type. Below is a list of (approximate) frequency ranges and some of the qualities found within them. For more on the subject, please go here.

Sub Bass (0-60 Hz)

0-25 Hz should automatically be filtered as no musical events occur here and too much energy only serves to muddy the sound.

25-60 Hz gives music a sense of power, once again, too much will give your sound an undefined low end.

Bass (60-250 Hz)

60-120 Hz is the place for the fundamentals of the bass and the low end of the kick.

60-250 Hz too much makes the sound thunderous, can thicken or thin the sound.

Misery Range (120-350 Hz)

Area most often in need of correction. Some portion of most instruments resides here creating undefined overlap.

Low Mid Range (250 Hz - 2 kHz)

Low order harmonics of most instruments. This range should be taken on a case by case basis.

If EQed improperly this range can sound nasal or cause listening fatigue.

Upper Mid Range (2-8 kHz)

2-4 kHz can mask speech recognition if too loud.

Slightly decreasing instruments at 3k and slightly increasing the vocal at 3k can make vocals more defined without increasing output.

4-6 kHz clarity and definition. Boosting makes the sound seem closer. Reducing 5k makes it distant.

2-8 kHz basic speech comprehensibility.

Upper Range (8-22 kHz)

8-12 kHz cymbals.

8-16 kHz clarity, too much causes sibilance.

12-22 kHz is air. Broad Q to give more air.

Sounds decrease in amplitude as they increase in frequency, as such there should be a treble fade out (high cut/low pass) in this section.


Quick Note on Gain

Channel level is another important aspect of mixing which begins to flesh itself out during the EQing process. As each new element is introduced for EQing, it is first imperative that you set a preliminary fader level to get the sound, more or less, tucked into your mix in terms of amplitude. To do so, simply raise the level of the new element until it is far too loud and then slowly lower its level until it naturally finds its pocket.


Gain Structure

Another side note on gain worth mentioning is gain structure. For those who don't know, gain structure is basically the act of keeping your levels in such a way that you do not raise gain at one point in your signal flow only to turn it down at a later stage (e.g. set the drum bus to +5 dB and the master at -1 dB), or excessively raising or lowering the levels at any one point in your signal chain.

A properly set gain structure is something that is always done in analogue mixing as improperly set levels will cause noise and other problems. In the digital domain this is also true, but to a lesser and sometimes non-existent degree; especially when working in a DAW such as Logic which supports a floating point architecture. Even so, it is a good idea to adhere to the concept of proper gain structure as much as possible.

To do so, simply try to keep your faders as close to unity (±0) as possible without overloading the inputs of any channel strip or plugin. Be careful though as your channel strips will usually only monitor the channel's output by default and some parameter settings will probably need to be changed in order to monitor the signal input at any one point in the chain.

Gain structure is different from overloading the channel output (over 0 dB of output) which largely needs no attention in DAWs which have a floating point architecture. You will not risk digital distortion in such instances on individual tracks. However, you can NEVER exceed 0 dB of output on the master out as the output becomes fixed and clipping and its subsequent digital distortion will occur.


General EQ Tips

Although the choice of a starting point is somewhat open to personal preference, it is essential to begin with a prominent groove element such as the kick or bass and build the groove around it one element at a time. Once the groove is sounding clean, add the other song elements one at a time while trying to clean up as much frequency overlap as possible.

No matter what element you are working with, the first thing you are going to want to do is add a low cut filter. To find where the low cut filter should be set, I generally start with it as steep as possible (48dB/octave or more) and sweep it up until the sound begins to loose some of its main tonal qualities. I then back down slightly on the frequency band until it is sounding natural and adjust the slope and Q to taste.

The next thing we want to do is to identify and eliminate any unnecessary or problem frequencies. To do this, we first need to listen to our sound in isolation for any resonances or other qualities that should not be there. If any are present, the most widely used method for EQing them (known as surgical EQing) is to set a bell filter to a very high Q and very high gain and sweep until the frequency we want eliminated becomes exaggerated. The next thing to do is to flip the gain so it is cutting rather than boosting. Finally, play with the Q, gain and frequency levels to fine tune.

Sometimes I have found it useful to cheat a little and simply start with the gain set so that it cuts immediately. I then sweep through the frequency range until the frequency I don't want disappears. I find this works well when there is a particularly wide band that needs filtering or the problem frequency is proving difficult to find under the conventional method. Whatever trick or method you employ is up to you as the sonic result is really the only thing that matters.

Finally we want to boost important frequencies in our sound. We do this in much the same way as the above method for eliminating frequencies in that we will start with a high gain, high Q bell filter and sweep until we are exaggerating the frequency we want to boost. The next step is to bring down the gain to a more moderate level and to open the Q to a relatively wide setting to give a gradual and wide boost, then fine tune the settings as necessary.

A rule of thumb in EQing is to cut with a narrow Q and extreme gain reduction and to boost with a wide Q and moderate to low gain increase. This is due to the fact that humans are much more sensitive to gains in amplitude than to reductions. You will notice this when you hear the resonance while sweeping to find the correct frequency as outlined above. The sound will be distinctly unnatural while the gain is boosting, but will smooth out and become natural when the gain is cutting, even at extreme settings.

Phase shift is also a concern as it always occurs when boosting. As such, it is a good idea to cut as much of what you don't want to hear as possible first and then boost the important areas somewhat conservatively. If you go straight to boosting only the frequencies you want to hear without first cutting, you are going to end up with (more or less) the same gain ratio between frequencies while introducing unwanted phase shift. This can create problems down the road and make it more difficult to cut out problem or unnecessary frequencies later on.

A classic Pultec EQ


Specific EQ Tips

Kick

I always start with the kick as that, for me, is the main grounding element and pulse of the song. The kick generally has a low center around 65-110 Hz and a head from 3-8 kHz. Immediately I will low cut the kick as much as possible to make room for the bass and then cut just above the low center (110-300 Hz) in order to clear the 'misery range' for other instruments. I will then use the low pass filter and cut the top as much as possible without making the head sound too dull. From here it is a matter of playing around a bit to see if anything else can/should be cut. After cutting, I will slightly boost some of the more important frequencies of the kick to bring out some of its distinct character. Below, you can see how I have set the EQ with a moderate Q setting on the low and high filter to add some resonance and punch.

This particular kick sample has been processed with a large amount of sub-bass on it which I am cutting along with a few other frequencies in order to make it sound a bit more clear and organic. If I decide to boost any of the frequencies later on, I will just add another EQ behind the first, as I have used all of my bell filters for cutting.

Snare

Next, I will go to the snare. One again, I will set the low cut filter as high and steep as possible and then back down a bit once the sound becomes too thin. I will then cut the top as much as possible with a low pass filter, being careful not to dull it. I will then try to pick out resonances in the sound and cut those frequencies if they are present (snares are notorious for having ringing overtones which may or may not be wanted).

I will then take the snare out of solo mode and listen to it with the kick to see how things sit. I will then try to increase the frequency setting of the low cut filter on the snare while using the low energy of the kick to compensate. This is done to help clear up the areas where the snare and kick overlap and create a more distinct separation of the two drums. I will then go through with a bell filter and sweep for frequencies that are not crucial to the snare (usually in the mid range). Next I will crisp things up with a high shelving boost and wide Q increase over the point (and any other important frequencies) of the snare.

Despite the above outline, this snare was pretty straight forward with only one bell filter used for cutting some unnecessary frequencies. The snare should always be outputting at about the same level as the kick.

Bass

I will always end up EQing the bass against a soloed kick for fine tuning, so with that in mind, we can add the bass now while the mix is still in its infancy. As always, I will start with a steep low cut and sweep up until the sound begins to dull. In the case of the bass, obviously, this does not take much as I will only be cutting around 25-40 Hz. I will then back off on the dB/octave ratio and adjust the Q and frequency to taste.

Next I am going to go in with a high cut, and bring that down until some of the twang of the bass dulls; then back off and adjust to taste. If there are any odd sounding frequencies or resonances, I will go through and cut those with the surgical EQ tactic. From here, I can try a number of things in both the cut and boost departments and keep whatever sounds best.

Here are a few tips and tricks in EQing bass to try out. The frequencies are generalizations, but they should be a good place to get you started.

  • Use a narrow Q @ 100-120 Hz & 140-160 Hz and boost one while cutting the other.
  • Boost @ 700-900 Hz for more clarity and attack.
  • Reduce 20-80 Hz to cut mud.
  • Boost 80-140 Hz to increase bass tone fundamentals.
  • Boost 130-200 Hz to increase overtones.
  • Boost @ 2.5-3 kHz for snap.
  • Give a moderate boost @ a low frequency and then another boost @ either .5 or 2x the first frequency (e.g. boost @ 50 and then 100 or boost @ 120 and then @ 60).

With this bass I ended up shelving the low and cutting @ 200 to decrease an overpowering low end. I raised some of the the higher frequencies to help some of the articulation stand out and used the boost @ 120 & @ 60 trick to bring back a little of the bass energy I cut previously.

Hi Hat

The high hat is fairly easy to EQ as it largely consists of harmonics which can be cut drastically to fit in a mix while still retaining a characteristic sound. Once again I will low cut this, while listening to the rest of the mix. This time, however, I will stop my low cut sweep when I hear the low end of the high hat get (more or less) clear of the the other instruments. Depending on the harmonics of the bass and snare, this can vary widely. If I have a bass or snare with rich upper harmonics, I will somewhat ignore the frequency overlap of the high hat and bass and sweep until things fit. If the bass/snare is very low with no snappiness or being cut with a large amount of low pass, I will pay more attention to the frequency overlap and stop when the frequencies of the hat and other instruments are clear of each other.

As I said, the values of the low cut can vary widely from 250-1000+ Hz depending on your genre, and what you are trying to accomplish sonically. The upper ranges of the high hat are going to make it more present, from 8-15+ kHz so this can be a good place to boost. I would also first recommend to surgically cut as much as possible from the upper end as the hat tends to take up a lot of upper harmonic space which is good to keep clear for other instruments and vocals.

The HH only needed a high and low cut filter in this instance.

Vocals

Vocals can be the most difficult to EQ as they tend to be the most expressive, individualistic and most often multi-tracked element of a song. A such, vocals are the most open to and in need of case by case interpretation. As usual, however, the first thing we are going to do is to low cut our vocal track(s) to the point we begin to lose the necessary low end. Once again, we immediately back off a bit on the frequency and steepness. Then we play around and fine tune all parameters to taste.

Next, I will once again do the same with a high cut filter until things dull, setting the frequency, steepness and Q as done with the low cut. I will then try to cut out any unwanted resonances which usually reside in the 120-350Hz range (and elsewhere if they are present). From here, I will cut to taste while keeping the sound thick. I will then try boosting @ 2 or 3 kHz depending on if it is a male or female in order to increase the comprehensibility.

It is recommended to cut sibilance by hand at every 'S' sound by automation rather than with a de-esser as it gives a more accurate result. This can be begun here as a rudimentary loop step just to give a general feel for how things sit, but the full on automation should occur later on as the vocal and track progress.

After playing around a bit and did some cutting and boosting as shown.

Secondary Instruments

There are not really any hard and fast rules for secondary instruments such as toms, synths and electric pianos, but some of the basic fundamentals discussed above can and should be incorporated. Basically, always start with a low cut/high pass filter, set it the way described and then do the same with a low pass/high cut. Cut unnecessary or obscene frequencies drastically with a high Q. Boost those that are necessary to the sound's character with a low Q and low boost.


Final Notes

Here is how our loop sounds after the first pass of EQing.

Before EQ

After EQ

You'll notice that the loop is now far less boomy and overpowering in the low end and the instrumentation and levels are much more clear and precise. The vocal now also sits much more naturally.

If this were a real project, I would then go back and begin to fine tune things by more accurately finding the frequencies fundamental to each sound and possibly add other EQs in serial to more distinctly shape the sound. I would then check instruments against each other and try to punch holes where I could in any frequency conflicts with a surgical EQ. I would do this in the same order as I began the EQing process (kick to snare to bass, etc.) as I want to fit more non-essential sounds around the essential elements and not vice-versa (i.e. always work from the ground up; framework first, then ornamentation).

While these are good general guidelines, you should remember they are general guidelines. Many instances will take you outside of these margins and you should not be unwilling to explore extremes in any of these cases. Boosting @ 10-15 dB may give you the sound you want in certain instances, so please do not confine yourself to .5 or 1 dB of gain just because it is suggested to boost conservatively. The real key is experimentation and practice.

Next time we will look a bit into compression, different compression types and how to implement them in our mix.

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