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Equalizer is probably the single most important tool in sound shaping, and most sound engineers probably would choose it, if it would have to be their only used processor. With the help of equalizer we can match tracks together, make different instruments sound in more uniform way, correct tonal balance between low, middle and high frequencies and shape the whole recording in such a way, that it starts to sound polished, natural and perfect.     

Equalizer - The Study of Action

More about equalizers and their practical application in the mix
How to use the Equalizer?

Parametric, graphic, paragraphic, the "Q" and low-hi-pass\shelf\bell. What does it mean and how to use it in my song?

For those who want more detailed, technical knowledge on the use of equalizers in the mix here are some little secrets and terminology from the studio kitchen. After applying them to your mix it will be much better. At the beginning let's get familiar with the technical jargon used in equalizers. A typical parametric equalizer has the ability to choose the 3 parameters for each of its filters. They are:

-FREQUENCY - frequency [Hz]
-GAIN          - raises or weakens certain frequencies in sound [db]
-"Q"            - otherwise called wideness of filter, defines the field of action of a filter                    

While the frequency and gain values of the equalizer do not require a major comment, the value of "Q" should be discussed here more in detail. This is a very important parameter influencing the sound of any equalizer very much. "Q" is determining how widely the frequencies surrounding the center, set frequency will be affected (boosted\weakened) by the gain parameter. Along with the desired frequency, some surrounding frequencies are affected and the "Q" sets how much of them are to be affected. Otherwise, you can say that this is the boldness of action filter.

The two following pictures show you clearly what is the difference between the wide "Q" and the narrow "Q":

The frequency of 1000 Hz = 1 kHz was boosted here by 5 decibels. We see, however, that the value of Q = 2.9.  The equalizer's filter begins "kicking in" from about 400 HZ and ends it's action  about 2500Hz. You can therefore say that it operates quite broadly. Let's look at the picture below:

Here the equalizer filter is also boosted by 5 decibels at 1000 Hz, but the value of "Q" is 12.6. You can easily notice that the frequency 1000 Hz is boosted only with a very small degree of the neighboring frequencies, and it is from some 750 Hz to about 1300 Hz. What practical difference does it  give when it comes to mixing the music?  In the first case of the wide "Q" accentuates the whole main middle bandwidth. It will give a warm, broad sound, and the volume of a track will be quite considerably increased, which would require to turn it down a little in volume.
In the second case, however, with a narrow "Q"  the track will not change in volume more than a hint, and the frequency of 1000 Hz is boosted very selectively, so it will not have such a large effect on sound, as in the first instance. Yet we should add here that this type of filter (or rather its shape), which was used in those 2 examples is called "Bell Filter", because it recalls the shape of a bell. There are other types of filters, which are described  below.

When to use a narrow band "O", and when the wide "Q"? Generally, it is understood that a broad "Q" gives a more natural sound. It should therefore be used where we do not want to alter the nature of the track too drastically, although obviously too rigid rules are not the case here. Narrow "Q" is often used  to get rid of some unnecessary frequencies, badly affecting the sound or even to cut out a hi frequency noise in the vicinity of 10 000 Hz, or low "brooming"  within the limits of 60 Hz. This is more surgical type of application.  Personally, we recommend applying the broader "Q" in all cases except the need of specialized approach to the sound problems, which is a precise, almost surgical interference in the spectrum. You should be careful here, because the deep cut in the track with narrow "Q" can cause the instrument tracks, voice or other sound very unnatural. In a broad variety of techno music styles this is a very common treatment and it is often deliberately used to make the equalizer as a type of FX and achieve extraordinary, shocking sounds.


How many  decibels is much, and how many is moderate? Crisp, decisive effect in audio spectrum change begins to be heard from about 3 decibels. For good material, excellently recorded  tracks  such changes are not necessary and a small change of simply about 0.5 - 1.5 decibels will do the trick of setting the optimal sound of a track. Again, however, there are absolutely no rules, unless the raise or cut should be applied in order to achieve the intended effect. We had cases of very well-known performers, whose mixes needed a raise in bass during mastering almost 20 decibels in order to lift the lost depth and ensure that the mix sounded  as good in terms of the lows, as the best commercial recordings heard on the radio. There is therefore the only rule in boosting or cutting with equalizer-that you need to raise or cut as much as necessary to achieve the intended effect, whether it is 2 or 15 db. And do not be afraid of turning knobs of  equalizer and looking for the right sound. This is a really powerful tool for shaping the sound, the importance of it simply can not be overestimated. It is probably the most important sound shaping tool.

The types of filters in equalizers
A typical parametric equalizer has a number of filters for a choice of the nature of action. The most flexible here are especially software equalizers, which capabilities have substantially exceeded that of  the hardware devices. Le's return to our example. The following 4 pictures show the 4 other types of filters, in addition to the main type called the "bell". They are:

-high shelf
-low shelf
-high cut

Here's the High Shelf filter. It works in such a way that everything above a chosen frequency has a comprehensive raise, thus giving shape resembling a shelf. The "Q" factor sets the steepness of transition to the shelve here.


Here we have a Low-Shelf. Everything that is below the desired frequency will be lowered, the "Q" sets out the steepness of the slope.

Hi Cut. This type of filter cuts quite steeply all the frequencies, which are above the desired frequency. The "Q" defines the steepness of the cut.

Low Cut. This type of filter cuts radically all the frequencies that are below the desired frequency. The "Q" defines the steepness of the cut. 

And here is the appearance of a typical graphic equalizer in the software version. There is no longer the ability to set the frequency and "Q" of each filter. The whole frequency band is divided on the sliders with a fixed value of the "Q" and each frequency  is adjusted only by the value of gain, whether boost, or cut. Seting the sliders gives a graphical picture of how the equalizer affects the spectrum:


Since the equalizer like that has a lot of (28) ranges of bands dividing the sound spectrum it can be used for a very selective raise or  cut, achieving the same effect as a narrow "Q" parametric equalizer. You can also arrange the position of sliders, respectively, to achieve the same effect as using various filters, parametric equalizer, that is, for example, "Hi Cut" or "Bell". Setting shelves or low\hi pass is also possible using this type of equalizer. It's advantage is very clear graphic representation of what is going on with the sound spectrum. 


The software equalizers are present on the market or in studios already  for a long time, their useability is in many respects higher than in the case of physical, hardware devices. However many experts still believe that the hardware ones are better. Why the hardware should be better  and what the legend of analog devices is derived from? Equalizers of software type are certainly not worse than analog devices. The best proof of it is that many very reputable studies use them regularly. There are more accurate and handy in use, they can save their settings for different uses. There are more and more software equalizers, many of them can imitate their analog counterparts to the high degree. It is worth mentioning that there are such equalizers as the Blue Tubes PEQ-2A for example which can successfully emulate the famous Pullmans, and are capable of simultaneously cut and raise the frequency selection, which gives a very distinctive sound, used on many legendary recordings, such as the legendary album "Paranoid" of Black Sabbath:

Blue Tubes- Pullman software emulation

Another excellent design of program equalizer is an outstanding Master Q from the Polish company PSP- Professional Sound Projects:

PSP- Professional Sound Projects- Master Q

Characterized by a very soft, full sound, the sound of this application reflects the sound of excellent analog equalizer.

At the end we would like to give you some very useful advices in the practical application of equalizers in mixing material.

At the very beginning of mixing or mastering it should be taken into account how and using what equipment-technique the material was recorded. If it was recorded directly to a computer workstation DAW without the use of the good sounding path to  shape the sound, you almost certainly will require fairly drastic use of equalizers at the mixing stage. Soloed tracks will sound great, but despite of their  mighty and clear sound when soloed, they will not want to sound good when played together, many instruments will be lost in the mix in spite of beautiful sound when soloed, the volume raise will not help and the whole mix will sound flat and dull. Similarly, if you use tracks created with VST instruments and they were rendered to zero, without the use of any processor, analog or software, their tracks will require the use of radical and skillful equalization. So do not expect your mix will sound great when everything is done on zero EQ, because it will not. 

If the recorded material has passed through gently and musically sounding analog devices, such as reel-to-reel tape decks or tube compressors shaping the sound in very desirable way, which were used initially in the studios, the tracks will no longer require such a big equalizer intervention. Equalizer may still be needed, but the sound will already shaped by smooth sounding devices so that it can be used with much less equalization.

During equalization of tracks you should always bear in mind 2 things: What to do in order to lift the most characteristic feature of a particular instrument or voice, as well as how to contrast different tracks with each other. Only the tracks that are somehow contrasted will be heard good and will work nicely together in the mix. The ear of a listener will always pick up the smallest nuances in such contrasts.

Instead raising the volume of an instrument, which is barely audible in the mix, try to find a certain frequency, which is characteristic for that instrument and boost it using equalizer. For example, kick drums do not have to occupy at all bass frequency taking the energy from another instruments, you can take advantage of the equalizer and shape it using two bands with a fairly narrow "Q", one in the bass area and another around 1000 Hz or even higher (find it), often even a small change of 2-3 db will greatly improve the audibility of the kick drum and make a very noticeable improvement in mix.

5 You should think of the mix as a giant puzzle. The tracks should be shaped to fit together. So, if you add some, say, 1.500 Hz one one track maybe it would sound better to remove the same frequency from another. It is worth experimenting and trying, because it helps to make the mix to glue together and sound as one piece. This leads to the better sounding tracks that are not mutually extinguishing their frequencies, but cooperate together as well adjusted  mechanism. Thus, every instrument should occupy its own place in the mix.

Equalization is one of the four methods used by engineers in the mix to improve the sound of the tracks. The other three are the stereo panorama placement, the volume and delay\acceleration of timing of the track in order to make it more distinguishable and thereby change the spectral characteristics in relation to the frequencies of other tracks. And yes, there is a fifth method of changing sound- the dynamics devices like the compressor and expander. This is also loved by engineers all around the world ;-).

Kick drum and bass are two instruments that make up the spectral-rhythmic foundation of the sound. It should be noted that they need to be set at frequencies with which they complement each other, rather than competing. It is not good to raise the same frequency either for the bass and the kick in the area of, for example, 80 Hz. Much better is to make the bass more punchy at 120 db, and the kick more deep at 80 Hz, or vice versa. Both instruments will sound excellent and working together much better, while at the same time they will be perfectly audible in the mixdown. It is very important to do it at mixing stage, because the mastering will not be able to fix the problem of the bass extinguishing the kick.

In addition, you might experiment with a cut of a lower middle of the sound spectrum. If we cut some bass in the vicinity of 250 Hz, where it is the most "mud" for bass guitar and actually many other instruments, while we add the slightly higher frequencies, about, say, 1800 Hz, the bass will perfectly clarify itself up against the kick. If you apply it to, say, electric guitar track, you might cut everything below 80 Hz using shelf filter, making the bass and the kick having more gain for themselves and giving even more space to the mix. There is a few things more desirable in a mix then the bass and kick nicely working together and complementing each other.

If we act similarly with each instrument of our song, cutting them at some  frequencies, and adding others, we will be able to find a great sounding effect of the tracks interlocking themselves in the mix and making one beautiful piece of art. 


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