Chapter 4 - Equalization
Now we arrive at the next big topic in mixing: that of equalization. Equalization, or EQ, is the process of changing the balance of the frequency components of sounds.
4.1 Purposes
In order to equalize successfully, you must first know what exactly you are trying to accomplish. Do not equalize unless you have a particular reason to do so. There are two main reasons to equalize a sound: to avoid masking, or to change the character of the sound.
4.1.1 Avoiding Masking
Masking is a phenomenon that occurs when you have multiple sounds, playing simultaneously, that occupy similar frequency ranges. It causes one or both of the sounds involved to be partially or entirely obscured. Masking is more pronounced in low frequencies; the lower you go, the more space your sounds need to retain clarity.
One of the most common and oft-discussed masking-related problems is the interaction of kick drums and basslines. In a typical pop or dance tune, the kick drum and the bassline together contain most of the low end of the music, and getting them to not interfere with each other is a constant problem for producers. If insufficient attention is paid to the interaction of the kick and the bass, then you may end up with a messy low-end.
The same sorts of problems can occur across the frequency range. You can get away with more in the midrange and treble than you can in the bass, but ultimately you always have to worry about masking.
To avoid masking, the most important thing is to simply select your sounds such that you avoid frequency range overlaps. Don't use two sounds that compete for the same frequency range. Those two sounds will never sound good together, no matter what you do to them.
If sound selection is your most important tool in fighting masking, then your next most important tool is equalization. With EQ, you can remove or deemphasize nonessential components of a sound, and emphasize the essential components of the sound. In this way you can reduce the effects of masking, by deciding what sound will dominate in each frequency range. To cause a sound to dominate in a given frequency range, cut other sounds in that frequency range, and/or boost the dominating sound in that frequency range.
Most sounds have energy across the majority of the audible spectrum, but with most of their energy focused in one or more "critical" frequency ranges. These critical ranges are the "essence" of the sound, and are typically the parts of it that will be heard clearly in the context of a mix. If you want a sound to be heard clearly in a mix, then you need to make sure that it dominates in its most important critical ranges.
Thus, the ideal approach to avoiding masking is this. Pick sounds that do not step on each others' critical ranges. Arrange your sounds so that their critical ranges fill out the frequency spectrum with a minimum of overlap. Then equalize your sounds — only as necessary — to emphasize their critical ranges, and to deemphasize nonessential frequencies when they detract from the clarity of the mix.
4.1.2 Changing Sound Character
Besides avoiding masking, equalization can be used to change the general char- acter of a sound. It can remove or deemphasize undesirable sound components, such as mud or resonances. It can also change the balance of desirable sound components (usually critical ranges). It can add sparkle to cymbals, impact to drums, and presence or fullness to instrumental lines, all by boosting or cutting different critical ranges. The boosts or cuts that one will use when changing the balance of critical ranges often depend on the desired psychological effect of the part; refer back to the breakdown of frequency ranges in Section 1.1.
4.2 Using a Parametric Equalizer
EQs are fairly intuitive to operate. We have all used them before; they are found, in simple form, in the tone controls of home stereo systems. The EQs that you use in mixing are not radically conceptually different from those tone controls: you have a frequency band, and you have a gain amount. But there are some important differences.
For the purposes of mixing, you want to be using a parametric EQ . A parametric EQ is a particular type of EQ which is well-suited to precise and nuanced adjustments of frequency balance. It consists of several "filters;" each of these filters creates a boost or a cut in a frequency range, and its behavior is controlled with three adjustable parameters: frequency, gain, and Q.
The "frequency" parameter sets the center frequency of the filter's action. The filter will not act on only this frequency; it will act on the center frequency and all of the frequencies surrounding it, with the intensity of the action steadily decreasing with distance from the center frequency.
The width of the affected frequency range is controlled by the "Q" parameter. Lower Q values result in wider ranges; higher Q values result in narrower ranges. A sufficiently high Q will result in essentially only the center frequency being affected.
The "gain" parameter is the simplest of the three parameters of a filter. It simply sets the amount of volume adjustment; specifically the amount of volume adjustment at the center frequency. A negative value will result in a cut, and a positive value will result in a boost.
So how do you decide on values for the frequency, gain, and Q of a given filter? As with leveling, there is a procedure that you can follow. In this procedure, first you find the frequency, and then you find the gain and Q more or less together.
4.2.1 Setting the Frequency
In finding the center frequency, you first need to decide what general frequency range you want to affect, and then what exact frequency you want to center on. Sometimes, particularly as you begin to develop your ear, you will know just from listening what frequency range you want to affect. If you don't know, then you need to spend some time analyzing the frequency content of your sound.
A spectrum analyzer can tell you where the critical ranges are (they will be the loudest portions of the frequency spectrum), and it can also tell you about the presence of any nonessential frequencies that you might want to cut. To get a more nuanced perspective on the frequency content of your sound, to really figure out what's what, you can also employ a method known as the "sweep technique."
To perform the sweep technique, set your filter to a medium Q and a high gain, and simply sweep it across the frequency spectrum, listening as you go. The sweep technique will tell you what the "ingredients" of your sound are, by letting you hear each frequency range individually. Once you have done a sweep, you will have a better idea of what each frequency range is contributing to your sound, and you will be better equipped to decide which ranges you want to boost and cut.
The sweep technique should be avoided whenever possible, for two reasons. First, it is very tiring to the ears. Second, after sweeping, your perception of the sound will be distorted, and you will no longer be in a good position to make judgments about EQ. Don't go to great lengths to avoid sweeping, but don't do it when it's not really necessary. You'll find that it becomes necessary less often as you begin to develop an ear for what the different frequency ranges sound like.
Presumably at this point you've decided on a frequency range that you want to boost or cut. Now you have to decide on a precise frequency to set as your center frequency. Sometimes it doesn't really matter; just put the center frequency in more or less the center of the range you want to affect. But if you have a tonal sound, then you can sometimes achieve a better effect by setting your center frequency to a prominent tonal frequency.[1]
To do this, you will want to employ the sweep technique again, except over a narrower range, and with a very high Q rather than a low Q. The high Q will allow you to "tune" your center frequency to a strong tonal frequency in the sound. You will know that you have done this when you hear a loud ringing sound.
4.2.2 Setting the Q and Gain
Once you have found your center frequency, you should fiddle with the gain and Q values until you arrive at a satisfactory result. When boosting, I find myself generally using low to moderate Q values (0.2-10) and less extreme gain values (0.2-4dB), while when cutting I find myself using higher Q values (7+) and more extreme (-2dB or lower) gain values. This is the case for a variety of reasons, as follows.
When boosting, typically I'm boosting a critical range, and often it sounds best to also give the frequencies around the critical range a slight boost, just to make the sound more natural. This accounts for the low Q value. The mild gain value is simply because it seldom sounds natural to give a single region of a sound an extreme boost, and it can actually sometimes result in noticeable phase "smearing," particularly with high Q values. This smearing can manifest, in its most blatant form, as sustained ringing near the center frequency.
You can, of course, cut critical ranges, in which case similar principles apply in terms of Q and gain settings. But, simply due to the nature of critical ranges, I don't usually want to cut them. More often I'm dipping in between critical ranges to try and remove undesired frequencies, and I don't want to cut the desired frequencies, so a high Q value gives me the precise action necessary to do this. I often use a fairly extreme gain value, simply because of the nature of what I'm trying to achieve; I'm trying to remove or substantially reduce undesired frequencies, not subtly reduce undesired frequencies.
None of these things should be taken as rules. These are merely common patterns. Don't be afraid to do a boost with a high Q and a high gain if the situation calls for it. As always, your ear is the final judge.
4.2.3 Evaluating Your Results
It can sometimes be hard to judge the results of your EQing. One technique that is helpful is to toggle the "bypass" button on your EQ on and off, to see what your EQing has done to the sound. Is it making the sound better, or worse? With extreme EQing the effects will be very obvious. With subtle EQing, particularly boosts and cuts less than 2dB or so in magnitude, they may be less so. In these cases, just sit back listen to the music for a while, and it should soon become apparent whether the EQ adjustments are helping or hurting the sound.
One final reminder. Always bear in mind that you're not EQing the sound to sound good by itself; you're EQing it to sound good in the context of the mix. So while listening to the sound by itself can be helpful, ultimately your judgments have to be based on how it sounds in the mix.
4.2.4 High Shelf/Low Shelf Filters
Thus far I have made an important omission. Parametric EQs usually supply you with a few different types of filters. In the preceding discussion we have examined only one type of filter: the bandpass filter. The bandpass filter is the most common and important type of filter, but a few other common types of filters also require discussion.
The next types of filter we will look at are the high shelf and low shelf filter. High and low shelf filters have the same parameters as bandpass filters: frequency, gain, and Q. A high shelf filter boosts or cuts all of the frequencies that are higher than its center frequency. A low shelf filter boosts or cuts all of the frequencies that are lower than its center frequency.
That is a simplification. A high shelf filter does not simply adjust the volume of all frequencies above its center frequency, and none of the frequencies below its center frequency. As with bandpass filters, there is a curve involved, with the Q value controlling the steepness of the curve. The center frequency is the frequency at which the volume adjustment is half as much as is promised by the gain value. The same applies to low shelf filters.
High/low shelf filters are most useful when adjusting the balance of critical ranges when those critical ranges happen to be all frequencies above or below a certain frequency. They are also useful for reducing, but not removing, undesirable frequencies of the same description. To entirely remove frequencies above or below a certain frequency, you should use a highpass or lowpass filter.
4.2.5 Highpass/Lowpass Filters
A highpass filter cuts all frequencies below a certain frequency. However, rather than cutting all of them by the same amount, as would a low shelf filter, the gain reduction becomes progressively more extreme with decreasing frequency, until the gain reduction is so extreme that it amounts to complete removal. A highpass filter has just one parameter: the cutoff frequency. The cutoff frequency is the center of the action of the filter; the filter has already begun to act somewhat at the cutoff frequency, but not very much.
A lowpass filter is just the opposite of a highpass filter. Rather than cutting all frequencies below the cutoff frequency, it cuts all frequencies above the cutoff frequency. Other than that it behaves the same.
Some lowpass/highpass filters will also have a "resonance" parameter, which may also be called Q. This resonance/Q parameter is rather unlike the Q parameter for bandpass filters. What it does is it causes the frequencies in a narrow band around the cutoff frequency to be boosted. The higher the resonance value, the more the frequencies are boosted.
4.3 Typical EQ Uses
EQing a sound usually involves a process of discovery. You figure out the com- ponents of the sound, and then decide how you want to balance out those components. Every sound is a little different; you can't EQ by formula. That said, there are a number of common patterns that you will begin to notice once you have EQed a lot of sounds. To give you a jump start, this section will list some of the most commonly noticed patterns.
There are a number of different sections, with each section addressing a specific type of sound. Each section begins with a list of commonly present frequency ranges and what quality they lend to the sound. To add more of a given quality to the sound, you should boost in the appropriate frequency range, and to give less of a given quality to a sound, you should cut in the same frequency range.
Always be aware of the concept of yin and yang. EQing is relative, not absolute. You may wonder why you would ever want to take away from a given quality in a sound, but the reason is simple: by taking away from one quality, you add to all of the other qualities. On the same token, by adding to one quality of a sound, you take away from the all of the other qualities. So you won't get anywhere by just boosting everything; you need to use your EQ to create a tasteful balance.
4.3.1 General
<40Hz: Subsonics. Remove frequencies in this range if present; they will not be audible in the mix, and will only eat up available headroom.
100-300Hz: Fullness, but also muddiness. Boosting this frequency range will fatten up a sound, but this range also tends to get crowded, so you may need to cut some things in here.
l-8kHz: Presence. The ear is very sensitive to this frequency range, and boost- ing critical ranges in here will make the listener really pay attention to the boosted instruments. But, boost too much, and you will end up with a very tiring and overbearing mix.
10-18kHz: Air. Boosting in this range will give your mix liveliness and excitement; cutting will make things mellower and more relaxing. Most sounds sound better with a little extra air, but do not boost everything in this range, or, as with any frequency range, you will end up with masking.
4.3.2 Kick Drums
40-80Hz: Gives the drum body.
80-120Hz: Gives the drum punchiness.
150-300Hz: Too much will make the drum sound muddy. Too little will make the drum sound pinched and unnatural.
l-8kHz:Gives the drum presence and punchiness.
&rt;8kHz: Contains the click at the attack of the drum.
4.3.3 Basslines
40-160Hz: Gives the bass smoothness and fullness.
140-400Hz: Gives the bass character and personality, as well as audibility on small speakers.
Basslines are hard to generalize about, because there is so much variety in them. The most important thing to think about when EQing your bassline is how it interacts with the kick drum. You will probably need to sacrifice something from each of them to make them work well together.
4.3.4 Snare Drums
180-220Hz: Gives the drum body.
200-300Hz: Gives the drum punchiness.
l-8kHz: Gives the drum presence and crack.
&rt;8kHz: Contains the attack click.
4.3.5 Cymbals
<lkHz: Low- frequency components. You may want to reduce or remove these, as they may be inaudible in the mix and muddy things up. A low shelf filter is usually what you want here; a highpass filter can be nice in that it can clear things up in a very busy mix, but you run a high risk of making the cymbal sound unnatural and disconnected from the rest of the mix.
2-8kHz: Gives the cymbal a metallic quality.
8-18kHz: Gives the cymbal sparkle and sizzle. Boost to add excitement. Cut to make the cymbals more soothing and less piercing.
4.3.6 Instruments
There are few specific claims that be made for tonal instruments, since they're all different. Refer to Section 4.3.1 for the usual generalities. Read on for some additional generalities.
With tonal instruments, particularly live instruments, you generally want to be gentler with your EQing than with non-tonal sounds and percussion. Low Q values are best in most cases.
The usual balance that one wants to strike for a tonal instrument is between three components:
The fundamental: The fundamental frequency of the tone (see Section 1.2.1), along with the first few harmonics, sort of hold the sound together and give it its "body."
The upper harmonics: The higher harmonics contain a lot of the character and personality of the sound, and boosting them can often bring out some interesting characteristics.
The treble: Even low instrument sounds often contain some interesting stuff in the treble range: attack clicks, "air," and the various scraping and shuffling sounds that are often present in live instrument recordings. Generally what I will do with these is either cut them or leave them be. If I want to bring them out, I will probably use some multiband compression[2], rather than boosting the treble.
4.3.7 Vocals
The same generalities apply for vocals as for instruments. The vowel part of the sound is in the midrange, while the consonant part is in the presence range. Vocals require even more gentleness with EQing than do instruments.
[1] It is generally profitable to pay particular attention to the precise center frequency when EQing sounds in the bass range. The main exception to this rule is when EQing to remove bass frequencies, in which case the center frequency is relatively unimportant.
[2] See Section 5.4.9.
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