Getting to know the audible frequency spectrum – that is, the range from 20Hz-20kHz – and where certain instruments and general sonic characteristics sit within it, is one of the cornerstones of any music producer’s ‘education’. Once you know exactly where you need to cut or boost, for example, a vocal or snare drum to get it sounding just so – as opposed to just sweeping your EQ’s frequency controls around speculatively – your engineering life becomes considerably easier, more productive and less chaotic. Intuition can get you a long way in mixing, sure, but understanding where any given sound source starts and ends in terms of hertz and kilohertz – a sort of ‘numerical classification’ of sound, if you will – is clearly advantageous, both creatively and workflow-wise.
In this feature, then, will take a whistle stop tour of the various discrete frequency ranges that make up the full audible spectrum, and summarise the instrumentation and mix elements that you can expect to find occupying each one, broadly speaking. Use this information to guide your administering of EQ, remembering that cutting one signal in two clashing mix elements is usually preferable to boosting the other, and that our ears are much more sensitive to some frequencies than others.
Sub bass: 20-60Hz
In this lowest of all the frequency ranges perceptible to the human ear, the movement of air is felt as much as it is heard, and you need a very big pair of monitors, or a dedicated subwoofer, to really make it happen (although a decent set of headphones will give a good enough impression). This is the range that causes the walls to shake and your trousers to flap, and greatly enhances any dance music experience, in particular.
To actually generate sounds in the sub bass region, you’ll need to push a bass guitar down to its very lower limits, or use a synthesiser or drum machine. Roland’s legendary TR-808 is perhaps the best known generator of sub sounds on the planet, but really, all you need is a single sine, triangle or square wave pitched down into sub-60Hz territory.
When it comes to EQing sub bass, less is very much more. In fact, your focus should be on high-pass filtering other sounds to get them out of the sub bass range, rather than boosting your actual sub element to make it heard over signals that shouldn’t really be down there in the first place.
Sitting, as the name suggests, just above the sub bass, the bass frequency range is where you’ll hear and feel the weight and solidity of a track, as primarily defined by its main bass instrument – be that a guitar or synth – and the kick drum. Even if they’re not blended layers within a synth patch, the bass and sub bass are meant to work together, and great care needs to be taken to keep their levels (individually and collectively) under control, as too much low end can overwhelm and ruin an otherwise good mix, while too little will result in a light, weedy sound. Also, generally, both should be in mono and positioned at the centre of the mix, in the interests of maintaining compatibility with mono playback systems (ie, club PAs) and the avoidance of potential phase issues.
Low mids: 250-500Hz
With most of the instruments in any mix having some degree of representation in the low mids – including, crucially, the fundamental frequencies of many vocals – it’s important to EQ them all as required to prevent clutter and confusion in this most precarious of ranges. Excessive volume here will result in a weird, boxy sound, while too little can suck the energy out your bass elements.
This all-important stretch of the spectrum is where the actual ‘notes’ of a track – ie, the fundamental frequencies of its constituent instruments and vocals – lie, so your priority here should be to bring the best out in the core of your melodies and ‘song’, without driving anything to the point at which it starts to sound ‘honky’, or pulling so much out that it comes across as brittle and ‘cheap’.
Upper mids: 2-4khz
The evolutionary imperative has led to the upper mids being the most sensitive area of the human auditory range. This is where vocal consonants reside, as well as the attack transients of snare drums and hi-hats, and the higher notes of pianos, strings and synths. Once again, tread with care in this domain, as small changes can have a profound impact.
The presence range is responsible for that ear-pleasing high-end texture, tangibility and lustre that every mix should exemplify. These are the frequencies to tweak when you want to improve the definition and gloss of synths, guitars, cymbal and vocals. Be aware, though, that with regard to the latter, it’s here that sibilance makes its, ahem, presence felt, so don’t overcook it unless you want your singer to sound harsh and irritating.
The very highest frequencies in the spectrum provide the sparkle and sheen of the instrument, vocal or mix in question, consisting, as they do, of nothing but harmonics (extreme synth programming aside). Give them a gentle boost when you need things to sound hyped and/or ‘airy’, but be careful not to make the signal too bright and fatiguing.
A number of modern EQs feature an ‘air’ band designed specifically for lifting this transformative range, cornering a high shelving boost at up to 40kHz – way higher than the 20kHz boundary of human hearing – in order to gradually ramp up the frequencies below to truly delicious effect. The careful application of an air band can really bring the high end detail and polish out in a mix.
For more on frequency ranges and how to manipulate them effectively, see our Beginner’s Guide to EQ.