Equalisers and Filters

Equalisers, or EQs, are devices that use filters in an array to modify the levels of parts of the frequency spectrum. They’re amazing for reducing harsh frequencies, sculpting sounds, and to create more precise targets for further processing, such as for compression based on a set frequency band (common with sidechains) or distortion (like with creating hardstyle kicks).

Most EQs you come across are parametric EQs, which come in various forms but generally have at least 3 bands, often a low shelf, band, and high shelf, but can also include low cuts, high cuts, and more bands between the shelves. They allow you to adjust the parameters of each filter including frequency at which they start to cut off, resonance or width, and volume. These filters can be thought of as lowpass, bandpass, and highpass filters in an array (but aren’t always this – check your EQ’s tech specs for more info). Parametric EQs that are missing features are called semi-parametric.

Dynamic EQ is a parametric EQ where each band has a fully-fledged compressor/expander on it. Combine your knowledge from above with your knowledge of compressors, and that’s how these work. You can disable the dynamic part, making them just parametric EQs, and you can disable bands making them just filters, AND you can make a giant band and use it as a normal compressor. I wouldn’t recommend this, but you can technically do it. A multiband compressor is basically a dynamic EQ without expansion.

Graphic EQs use sliders to adjust volume at set frequencies, typically at 1/3 octave intervals but sometimes with larger gaps between cutoff frequencies. I personally enjoy these, but they’re not practical in most cases.

A shelving EQ is like a parametric EQ but with only a high and low shelf, and are often missing resonance/width controls. These are often found in vintage consoles and guitar amps, and great for creating smile curves.

Filters are fun and if you’re gonna be using EQs or synths, you need to know what a filter is, what it does, and how it works. Filters, as the name implies, filter out, or remove, certain frequencies. Four filter types are common, and can be combined to create new filter types, as seen in the Matrix Filter and EQs:

• Lowpass, which only passes low frequencies/filters out high frequencies, and is the most common. This can also be called a high cut.

• Highpass, which only passes high frequencies/filters out low frequencies; also called low cut.

• Bandpass, which only passes a band of frequencies/filters out frequencies higher and lower than that band.

• Notch, which only passes high and low frequencies/filters out a band of frequencies.

Where the filter cuts off frequencies is called the cutoff frequency. How much emphasis the filter places around the cutoff frequency, or where a peak forms at the cutoff frequency (also determining width of a bandpass or notch filter), is determined by resonance, or feedback within filter.

EQs often make use of filters that combine some of the above to create things such as shelves, bells, and notches. These filters are effectivly highpass/lowpass filters, bandpass filters, and notch filters, BUT with the important difference of being combined with the original signal so as to have a limited cut or boost. Since most filters cut to infinity (how quickly depends on slope), and EQs don’t, the best way is to let a bit of the original signal through, so just that filter’s effect is lessened, creating the typical 6-12db boosts and cuts you see in EQs.