How EQ and Compression Can Make or Break Your Mix (Part 1)


What is EQ?
What is compression?  
When do I use them, and in what order?

These are some very important (and common) mixing questions that we’ll be tackling in this two-part series on EQ and compression. Whether you’re a DIY producer who wants to improve your mixes, or simply a musician who’d like to understand some of theory behind music production, these tips are sure to improve the quality of your music!

First, an important caveat…

There are very few hard and fast rules when it comes to music production. Rather, there are only different things you can do depending on the outcome you want to achieve.  At the end of the day, creativity is key!  

Having said that, there are a number of tried-and-tested techniques that have worked for us – and many others – that you should consider when you get down to mixing.  Our suggestion is therefore to try everything out for yourself, and see what works for you! 

With that in mind, let’s get straight down to it – starting with EQ. 

EQ is EZ

EQ, or equalisation, refers to the process of adjusting sound frequencies within an electronic signal. Most listeners are familiar with this concept when it comes manipulating the bass or treble response of a sound system. For music producers, however, EQ can be a complex and valuable tool. Using EQ, we can sonically manipulate a track or entire song to increase the perceived loudness of a mix, surgically remove unpleasant frequencies, or even change the feel of the music entirely. 

In basic terms, when you record music, you’re effectively converting that analog audio signal into stored digital data.  That signal is made up of a number of sound frequencies, which sit on a spectrum. Those frequencies are described using a unit of measurement known as ‘hertz’ (or ‘Hz’ for short).  Each musical note has a fundamental frequency, which our brains interpret as pitch. Lower sounds (kick drum, bass guitar) sit on the lower end of the spectrum, and vibrate at a lower Hz, while higher sounds (such as a vocal or hi-hat) sit on the higher end of the spectrum, vibrating at a higher Hz.

A great place to start working with EQ, is to sweep across the frequencies and find sounds you think are pleasing, or displeasing. EQ allows you to affect the prominence of these frequencies, or remove them entirely, by increasing or decreasing the gain at those frequencies.  For example, if you wanted to emphasise the sound of a pick strumming an acoustic guitar (a sound which generally sits at around 5000Hz), you could adjust the EQ by raising the volume of the signal at 5000Hz.  Likewise, if you wanted to de-emphasise that sound, you could simply decrease the gain at that frequency. 

High pass filters 

There are a number of EQ techniques you can use to achieve different sounding mixes.  But perhaps the most important of them all is high pass filtering

High pass filtering involves adjusting the EQ to allow high sound frequencies to pass through, while removing low sound frequencies. 

As noted above, when we record music, our recording equipment picks up a range of sounds which it converts to electronic signals along a frequency spectrum.   A couple of issues arise from this.

First, not all of this sound is useful or useable.  Most people, for example, can’t hear frequencies below 30Hz, and most speaker systems cannot replicate frequencies this low.  Yet sounds at such frequencies, such as the rumble of air conditioning system, will still be picked up when recording. 

Secondly, too much information at a particular frequency range (and specifically, low frequencies) can make your mix sound muddy and limit how hard you can compress and distort your mix. This can affect the overall perceived loudness and clearness of your track.  For instance, frequencies in the 30Hz - 80Hz are commonly associated with the kick and bass guitar sounds, but most other instruments such as synths, piano, guitars, strings and vocals also produce sound in this range.

Depending on how many tracks you have in your song, gently (or aggressively) high passing some or all of these instruments will leave space for the kick and bass and keep your mix clear and pumping. 

As a general rule, we do this by: 

1.    Removing signals below 30Hz by applying a steep, 48db gradient; and 

2.    Rolling off signals between 30Hz – 100Hz by applying a more gentle, 6db – 12db gradient. The aim here is to control the low end, not remove it entirely. 

On a standard EQ plugin, these steps look something like this: 

High pass filter at around 30Hz

High pass filter at around 30Hz

High pass filter with a more gentle ‘roll off’ between the 30 - 100Hz area

High pass filter with a more gentle ‘roll off’ between the 30 - 100Hz area

This should provide you with a good, general base which you can then use to make further, more specific EQ tweaks.  

Low pass filters

Just as there are high pass filters, so too are there low pass filters!  A low pass filter operates on the same logic set out above, but instead allows lower frequencies to pass through.

Example of a low pass filter

Example of a low pass filter

The applications of low pass filtering are not as cut and dry and high pass filtering. Low pass filtering can be used on tracks to remove a nasty hiss or buzz, or in the case of vocals, jarring high frequency consonants (in which case you’re better off using a smarter tool than a graphic EQ - a ‘de-esser’). If you’re a guitarist, then you’re already familiar with a type of low-pass filter. The ‘tone’ knob on guitars and amplifiers is a low pass filter that allows you to adjust the treble response of your guitar. 

Low pass filters can also be used to help create a sense of warmth. Much of the character and tone that comes from using old vintage gear and microphones can be attributed to the loss (and distortion) of higher frequencies as they travel through imperfect analogue equipment. Adding a low pass filter to your tracks can help emulate this sound, and provide some ‘glue’ to make your tracks sound like they are coming from the same sonic space. Removing too much of the high frequencies can result in a loss of air and shimmer in your mix, so ultimately this is an ingredient best used to taste.

In summary…

EQ is a critical tool for anyone looking to improve their mixes, and while largely open to creative interpretation, by applying simple and reliable techniques like high pass and low pass filtering (and with some practise!) you’re guaranteed to see your mixes improve. 

In our next article, we’ll discuss how compression comes into this process – and when and how it interacts with EQ!  

Cameron Jang