Art of Equalization
Mastering the art of equalization (EQ) is not an easy task. Yet, proper use of equalization is fundamental to mixing.
To put it simply, equalization is a combination of filters that “sculpts” sound by attenuating or boosting a selection of frequencies. What is more, EQ can be used in a corrective manner (to mend undesirable content) or in a creative manner (to add content to the sound).
Following this further, the audible frequency spectrum is often divided into 3 main ranges – low, mid, and high. In addition, the mid range is typically divided into “low-mid” and “high-mid” ranges as well.
A “spectrum analyzer” is a very useful graphic representation of the balance of frequencies in a signal. Moreover, they are typically laid out with frequency on the “x” axis and amplitude on the “y” axis with frequency scaled logarithmic (in octave or 3rd octave bands) and amplitude scaled linearly. Furthermore, Spectrum Analyzers update in real time as the signal is processed. Keep in mind – due to the “loudness perception”, the levels you see are not exactly the levels you are perceiving. For example, at the same mechanical/electrical dB level – low end seems quieter than high end because human ears are not very sensitive to low end. In other words, a truly balanced mix may appear unbalanced on an analyzer. So, when it comes to equalization, EARS OVER EYES!
DIVISIONS OF THE AUDIBLE FREQUENCY SPECTRUM AND THEIR ASSOCIATED DESCRIPTORS
20 – 50 Hz
Firstly, very difficult to distinguish pitches. Nearly subsonic
Also, powerful, thunderous rumble
Lastly, often undesirable
50 – 100 Hz
Generally, range in which pitch begins to be distinguishable.
In addition, the “sub” (fundamentals) of kick drums and bass.
Deep. thick and solid.
On the whole, you’ll seem to “feel” this range within your body rather than hear it.
100 – 200 Hz
Generally, fat and Rich.
Provides a sense of “body”.
Very “natural” sounding.
Overall, punchy – especially in percussion.
200 – 500 Hz
Colorful and warm – especially in guitar and piano.
In excess, can cause a “muddy” or a “boxy”.
500 – 1000 Hz
Tricky to manage. Easy to neglect.
Fragile and temperamental.
In excess, can sound hollow and and nasally.
In deficiency, can sound distant and dark.
2000 – 5000K
Be careful – humans are MOST sensitive this range. This is the range in which babies cry, metal objects clang, and “sibilance” occurs (“S” sounds).
Loud and present.
Defined and clear.
Edgy and biting.
In excess, harsh and painful.
In deficiency, distant and dark.
5000 – 10000 Hz
Crispy and Bright.
Sparkly and Brilliant.
In excess, harsh and “blinding”.
In deficiency, distant and and dark.
10000 – 20000 Hz
Sizzling and “airy”.
Atmospheric and brilliant.
Somewhat difficult to distinguish pitch.
In excess, harsh.
In deficiency, dull.
Can make vocals too “breathy”.
TYPES OF FILTERS
In this section I will brush over the implementation of some common types of filters found in equalizers. Bear in mind, some types of filters are more suitable for audio than others.
This equalizer is one of the simplest. As a matter of fact, you have probably used one on your car stereo system. Yet, it is often found in hi-fidelity audio equipment. Furthermore, it offers control over two ranges – bass and treble – using non-resonant, low and high “shelves”. The two ranges can be attenuated or boosted by lifting/lowering the gain of their respective shelf.
Bell filters boost/attenuate ranges of frequencies centred around a certain point. The specified point is effected the most, frequencies further from the point are affected less.
This is the most widely used audio equalizer of the 20th century because of its adaptability and intuitiveness. It typically has 10 “octave bands” (30 Hz, 60 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz), providing the highest degree of control.
Invented by world-renowned mastering engineer, George Massenburg, this equalizer allows for “surgical” equalization. Specifically, it features variable frequency, bandwidth, and gain – providing the highest degree of control of any type of filter.
SOME EQUALIZATION TECHNIQUES
The purpose of the mid-side technology is to separate information that is common to both the left and right channels (mono) and information that differs between channels (stereo) so that the user can manipulate them separately and check for consistency. With this technique you may want to boost your “sides” to achieve clarity and dimension while narrowing and high-pass filtering “mids” to provide focus and punch.
Spectral-matching equalizers analyze the spectrum of a reference track and and calculate the differences in level between the frequencies in it and your track. Then, it adjusts your track to match the balance of the reference using a multitude of “snap-shots” of each spectrum. Check out the spectral-matching functionality in iZotope’s Ozone.
The key feature of this type of EQ is the ability to control bands of frequencies dynamically. In many ways, it works like a “multi-band” compressor. An envelope follower controls the gain of an EQ band. Surely, the most practical use of dynamic EQ is on vocals as a “de-esser”. “De-essers” do exactly what they sound like they do. They counteract harshness caused by sibilance (“s” sounds).
Here is a good example of an advanced pairing of EQ and compression. Indeed, this technique works best on dynamic recordings.
Duplicate (or send to a return track) the track you wish to affect and heavily compress the duplicate. Automate the levels of the two so that the compressed track is dominant during quiet passages and the dynamic track is dominant during the loud passages. This opens up a lot of interesting possibilities when the two tracks have different EQ applied to them.
In conclusion, less is more – meaning, subtle changes are usually more effective than extreme changes. To conclude, keep in mind that EQ requires time and careful listening.