In this blog, I just want to go over the very basics of EQ. Just having a quick refresh on these basics will go a long way when making tonal decisions for your mix / master session!
Very simply, EQ can be thought of as a level control for frequency. They use specialized filters that influence the volume of specified frequencies or a range of frequencies within the audio spectrum.
EQ is mainly used to adjust (shape) the tone and character (timbre) of a sound; by either boosting or cutting frequencies. You can’t completely change a sound by using EQ; you can only cut, reduce, remove or exaggerate (boost) frequencies already present in the sound.
Equalizers are the essential tools used to achieve clarity, depth, tonal balance, and presence.
There are different types of filters and some terms specific to equalizers you need to know.
Types of filters
Low Cut Filter
A low cut filter removes all frequencies below a specified frequency cut-off point. This filter is also known as a high pass filter because it passes (leaves unaffected) all high frequencies above the set cut-off point. Low cut filters are generally used to remove unwanted or problematic low frequencies. Another great use for low cut Frequency filters is to automate them to create sweeping effects.
High Cut filter
A high cut filter removes all frequencies above a specified frequency cut-off point. This filter is also known as a low pass filter because it passes (leaves unaffected) all low frequencies below the set cut-off point. High cut filters are typically used to remove unwanted or problematic high frequencies; but they are also very useful to automate to create sweeping effects.
Low Shelf filter
The difference between a low shelf filter and low cut filter is that a low shelf filter attenuates or boosts frequencies below a specified frequency point. Low shelf filters don’t cut frequencies out completely like low cut filters. Instead, low shelf filters gradually reduce or boost the frequencies below the set or selected frequency by an equal amount. frequencies.
High Shelf filter
A high shelf filter attenuates or boosts frequencies above a specified frequency point. High shelf filters don’t cut frequencies out completely like high cut filters. Instead, they gradually reduce or boost treble frequencies.
High and low shelf filters are excellent choices to boost or reduce high-end frequencies without cutting them off completely. They are also specifically useful to make broad, musical tonal changes.
Bell Curve Filter
Bell curves (peak/dip filters) boost/cut a frequency and its surrounding frequencies at a set point. In a parametric equalizer, you can choose the frequency, the gain amount & set the bandwidth/Q. The Q or resonance is the shape or slope of the filter and can be narrow or wide. This determines how many frequencies either side of your centre (selected) frequency is affected by the gain boost or cut amount.
Narrow Qs with very high numbers are called notch filters and they are specific to a specific frequency; whereas a wider or lower number Q will affect more frequencies either side of your selected frequency. This is what makes the bell curve the most versatile filters. You can use them to boost or reduce a range of frequencies with precision; either to boost musical frequency areas; or for more surgical corrective work that requires accuracy.
Baxandall EQs are shelf filters based on a circuit designed by Peter Baxandall in 1952. They are particularly favoured as they have a wide Q that includes frequencies outside the range of hearing; and they transparently boost low and high end. So, they can really influence the sound of a mix without introducing too much colour.
A very useful filter to use in mastering applications.
Band pass filter
A band pass filter is used to isolate a range of frequencies by passing a range of frequencies around a specified centre frequency point. The low and high frequencies outside the range are attenuated. In multiband EQs, multiple band pass filters are used to divide the audio spectrum into sections.
A notch filter (sometimes called a band stop filter) attenuates a range of frequencies around a specified centre frequency point. So, the low and high frequencies pass on either side of the selected frequency; and only the selected frequency is addressed.
Notch filters are very useful to help correct specific resonance issues in a track; or for precise tonal shaping.
To help you refine your skill, please watch the video on EQ for an explanation on how the different filters work!