EQ and Filters Explained

The terms EQ and filter seem to mean different things, Filtering is generally what we say when we want to remove frequencies, and EQ is when we want to shape the sound by boosting and cutting.
The truth is, it’s all filtering.

Parameters
Cutoff or Frequency – Selects the frequency to adjust. This is measured in Hertz
Gain – how much boost or attenuation at the cutoff frequency. This is measured in decibels
Shape or type – this chooses what kind of filter you will be using. The filter shapes are Hi and low pass, band pass, peaking, notch, and shelf.
Quality or Bandwidth – usually just referred to as Q is the shape of the eq curve and how much of the surrounding frequencies will be affected.

What does an equalizer actually do?
An equalizer adjusts the balance of frequencies across the audible range. EQ is an incredibly powerful tool for crafting a mix.

Filter Shapes
A low pass filter also known as high cut filter removes frequencies above the cutoff.
A high pass filter or low cut filter does the opposite, it removes everything below the cutoff.

Low Pass Filter Example

High Pass Filter Example

When you use both these filter types at once it’s called a band pass filter, the top and bottom frequencies are removed.
With these three filter shapes Q effects the steepness of the filter.

Band Pass Filter Example

A notch filter is the opposite of a band pass filter, it lets all frequencies through except for a narrow notch in the spectrum which is attenuated greatly. The Q effects the width of the notch.

Notch Filter Example

There are two filter shapes that allows you to control how much the frequency will be attenuated.
A low shelf will boost or cut anything below the cutoff, a high shelf gives you boost or cut above the cutoff. You can choose how steep the slope is with the Q control.

Low Shelf Example

High Shelf Example

A peaking filter is also known as a bell curve, you can boost or cut any frequency with a peak at the cutoff and a slope on either side.

Peaking Filter Example

EQ Designs
There are two main types of EQ designs: Graphic and Parametric.
Graphic Equalizers have multiple peaking filters at specific frequency bands and give you a few overlapping frequency bands with adjustable gain. These are most commonly seen on consumer music players, but in professional audio these are very useful for mixing live music.
Parametric Equalizers give you the most flexibility you can choose the shape, cutoff, gain, and quality.
This is the type you will be using when mixing. Nearly all plugin equalizers will be parametric.

EQ Usage Tips

• Use your hi pass filters to remove unnecessary low frequencies from your tracks.
• Use notch filters to remove unwanted noises from a recording.
• Get rid of the frequencies you don’t need before boosting the ones you do, although it may not be your first instinct when eqing, it works a lot better.
• High q values will cause ringing or oscillation when boosted, this is not usually something you want to happen.
• Adjust the EQ so that the level remains constant whether engaged or bypasses, it’s too easy to be fooled by louder being better.