The Music Espionage

EQ


Studio audio is not about capturing every frequency of every sound: it is about creating a polished track that highlights the best of each instrument. Because of this, equalization is one of the main audio effects that will be used on nearly all tracks, to clean and shape the sound.

EQ has a vast assortment of applications that is can be used for in both live sound reinforcement and studio production.

Areas of the Audio Spectrum:
The first challenge when equalising musical sounds is in deciding which area of the frequency spectrum corresponds to which element of a sound’s timbre. If you want to emphasise the slap of a bass drum kit, where should you boost? Alternatively, if your guitar sounds boxy, where can you cut most effectively?

When it comes to equalising it will naturally help if you have a rough idea where the sound or noise lives, you are then able to boost this area, meaning you hear more of it, or cut it, meaning you hear less of it.

Knowing these bands and what fundamentals, harmonics and principally what instruments reside in these areas will greatly help when you are listening back to a recording and getting ready for post-production mixing.

Parametric EQ:
One type of equalization unit that uses bands to break the frequency spectrum into different areas of control is parametric EQ. These units are very common in modern recording studios and live sound applications and because of this become an extremely popular form of EQ for Digital Audio Workstations.

These examples are shown on Logic Pro, but the controls/parameters are the same not matter what, software or hardware.

Step 1 – Frequency:
The first thing to consider with this category of EQ is “where”. What area of the audio spectrum to I want to adjust; Low frequencies such as bass guitar and kick drums towards the left, mid frequencies such as electric guitar and vocals in the middle, or higher frequencies like crash cymbals on the right.

Step 2 – Gain:
The EQ will have no effect without some gain reduction or addition, no matter what you do with the other controls. Gain determines how much of a certain frequency is added, this is called boosting, or how much a frequency is removed, this is called cutting. Gain is the vertical axis on the EQ graph, from the bottom to the top.

Step 3 – Bandwidth or ‘Q’:
The final main element that is the same for all Parametric EQ units is the bandwidth, often called “Q” or the bell shape. This determines how wide or narrow the EQ band is. Low settings will result in a wider range of frequencies affected, while a higher setting will only affect a very small range of frequencies. This parameter is very useful if you want to affect a large area of frequencies or select just a narrow range of frequencies for very precise EQ.

The following tutorial highlights how to use a Parametric EQ in a DAW.

Graphic EQ:
The graphic equalizer is the second most common type of unit. This EQ has a range of faders that control the level of individual band-pass filter circuits, these dealing with their own specific frequency range. So each fader deals with a very small area of the frequency spectrum. Moving the fader up boosts that range, and moving the fader down reduces it. The combined effect of the filters is to change the overall balance of frequencies.

Professional graphic equalizers often split the frequencies down into 31 bands, this is commonly called a 1/3 octave, because each fader controls one third of an octave, so after every three faders the frequency is doubled.

Other amounts of band ranges are also used, for example ten-band (so each fader controls an octave) and fifteen-band (2/3 octave). These types are generally not considered adequate for live applications, as each frequency band is too broad for anything more than approximate tone shaping, but they are common for instrument tone control for example electric guitar and bass.

Types of EQ:
No matter what category of EQ unit you are using, graphic or parametric, there are certain varieties of EQ settings. These are common adjustment to bands of frequencies that allow you to create a certain affect and alter a range of frequencies.

High and Low Pass Filter:
Common shapes fashioned within equalisers are high-pass and low-pass filters. A high-pass filter (sometimes called a low-cut filter) progressively reduces the level of any audio frequencies below a user-specified ‘cutoff’ frequency, while leaving the level of those above this point comparatively unchanged. The low-pass filter (sometimes called a high-cut filter) reduces the level of frequencies above the cutoff point, leaving those below comparatively unchanged.

Shelving EQ:
In shelving equalization, all frequencies above or below a certain point are boosted or attenuated the same amount. This creates a “shelf” in the frequency spectrum. They are designed to apply an equal gain change to all frequencies beyond a user-selected shelving frequency, rather than applying a progressive gain change beyond a cutoff point, like a high or low pass filter.

Notch Filter – Band Pass:
Bell equalization boosts or attenuates a range of frequencies centered on a certain point. The specified point is affected the most; frequencies further from the point are affected less. Depending on the “Q” or bandwidth more or less of the adjacent frequencies are affected.

A good example of using notch filters is if you want to create a ‘Lo-fi’ effect, maybe on vocals to producer some interesting tonal characteristics. For this you need both high and low pass filters, set to somewhere around 1 and 4 kHz. And then a slight presence peak at around 3kHz, this cutting-off of the bass and treble gives you that classic lo-fi telephone effect.