Enmore Audio

Understanding the channel strip part II: equalisation

In the first article of this series, we discovered the purpose and functionality of the preamp. Although preamps can leave an indelible impression on the sound of a signal, that’s not its express purpose. Traditionally, as we descend the ladder slippery slope of the channel strip, the next stop is the equaliser section, or EQ for short.

The EQ’s job is to definitively colour the sound, and therefore is an incredibly powerful tool for sculpting signal. From an aesthetic standpoint, EQ can be subtle to the point where it’s not heard, only felt, or it can be liberally applied to satisfy the urge for extreme tone.

In a technical sense, EQ can be used to salvage inaudible recordings, or to tame the resonant idiosyncrasies of a theatre. In this article, we’ll ask why EQ is so important, have a broad look at the different parameters of EQ and how it has crossed over into the digital domain.ua 6176

Here is part two of our series of articles across the channel strip; this time we take a look at the ever-critical EQ section.

EQ and the Frequency Spectrum

Even to the uninitiated, judging sound in subjective terms is easy to understand. For example, if someone describes as sound as “boomy” or “harsh”, it shouldn’t be too hard to develop a mental picture of that sound.

Even if you can think of sound generic terms this broad, you have some understanding of the frequency spectrum. The spectrum of human hearing is measured in hertz (hz), the lowest being 20 hz, the highest 20,000 hz. So if a sound is boomy, woofy or bassy, frequencies at the lower end of spectrum are predominant; if it is harsh, tinny or metallic, the higher frequencies are more prominent.

If a sound is too boomy for example, or not boomy enough, you have to reach for the EQ. And as you can imagine, every sound has a character that can be described in these terms – EQing a sound therefore, is a massive part of a sound engineer’s job.

EQ Parameters


On physical channel strips the EQ section starts with the control of the high end frequencies at the top, the mid range frequencies below that, and lastly, the bottom end frequencies. With each of these bands of frequencies, the user can either cut or boost them by decibel increments.

The highest EQ setting is usually a shelf – a fixed point at which all frequencies above can be cut or boosted by the same amount. This is usually set very high, at frequencies that are not necessarily discernible in musical instruments (except for cymbals, hi hats and other piercing metallic instruments) and is generally used to add a subtle sense of airiness, or tame the overly harsh top end of a sound.


The effect of mid frequency EQ is much more apparent because the majority of audible sound happens in this band of the spectrum. Depending on the depth of the EQ section, this band can be split into high-mid (affecting sounds like the human voice, upper registers of the piano and guitar, woodwinds, high strings and much more) and low-mid (snare drum and toms, piano, guitar and bass, lower strings, brass etc) divisions.

Often the mid EQ is “sweepable”, meaning that the user can sweep through the frequencies of that band to cut and boost with more accuracy. Less common on analog mixing consoles is the parametric EQ: this means that along with the ability to dial in a desired frequency, the bandwidth or “Q” setting can be made more narrow or wide. This is especially useful for surgically cutting particular problem frequencies without losing a wide range of neighbouring sound from that part of the spectrum.


Bottom end EQ can sometimes be in the form of a shelf: just like the high frequency shelf, except the cutting or boosting affects the sound below a fixed point. Arguably though, more sensitive and precise EQ of the low end frequencies is important because there is a lot important musical information residing in this band (kick drums and bass guitars to name two), potentially muddying the waters: accurate EQ-ing in this band is vital in maintaining overall clarity.

In the Box

On a real life mixing desk, there’s little opportunity to visualise the shapes into which an EQ’d sound is being sculpted: you just have to use your ears (which is not a bad thing!). Surely one of the benefits of using an EQ plugin in a DAW project is the way that it presents the frequency spectrum in an easy to navigate interface, where cutting and boosting can be a simple as clicking and dragging a horizontal line.

The potential dangers of such an approach links back to using your ears: we can become accustomed to the way a particular EQ curve looks rather than sounds, and EQ decisions can be compromised by the eye overruling the ear.

There is however, no shortage of options when it comes to software emulations of classic EQ sections from analog mixing consoles, complete with the original visual interface. Plugin companies like Waves and Universal Audio create a multitude of rigorously faithful EQ tributes to the likes of SSL, Neve and API – who built some the world’s most celebrated consoles.

Sitting toward the top of the console, the EQ is often the first part of the signal chain that reshapes the sound coming from the microphone. Thus it’s important to recognise its power to enhance or detrimentally affect a sound. Whether it be on a mixing desk, or in plugin form, familiarity with the nuances of a particular EQ can help an engineer commit the best possible sound to tape, or carve out unique sonic characters in the mix.