The equalizer is a device that can control and alter the frequency content of a signal in many different ways. Changing this frequency content alters the tone and harmonic make-up of that sound.
Learning how to use one is a vital skill to develop in the studio. During mixing, you need to blend together lots of different sounds to make a cohesive whole and one of the areas where you can achieve this is through the use of EQ.
You find EQ controls on the channel strips of mixing boards, both on hardware devices and in software programs:
A graphic EQ is a piece of rack-mount equipment that provides more precise control of the frequency content of the inputted signal:
What is an Equalizer Used For?
An equalizer (also seen as equaliser) can be used as a correction tool or as a creative tool. It depends on the reasons behind your use of the device. Some of the most common uses are:
- To remove specific frequencies to help enable a sound to sit better in the mix. For example, it’s quite common to cut the frequencies of an electric guitar below 100-150 Hz, as removing them helps create more room for the bass guitar‘s frequency content. In fact, this is something that I always do when mixing.
- A graphic EQ unit is often used to zoom in on specific problem frequencies, and then remove them. For example, you may find that a guitar recording you made has an annoying resonant frequency that stands out too much – one of those annoying notes that seems to ‘ring’. You can use the device to focus in on the narrow frequency range around it, and then cut it.
- The controls on the mixing console can be used to help separate two recordings that would otherwise sound too similar. A simple method I often use if I have two similar guitar tracks is to boost one track around the 3 kHz range and the other around the 4 kHz range -this helps to contrast the two tracks inside a mix.
These are just a few of the many possible uses for this important piece of equipment.
Types of EQ
There are different types of EQ filters, each of which are suited to different scenarios. We can look at some of these below.
- The hi-pass filter: cuts all frequencies below a specified cut-off point (FC), which allows higher frequencies to pass through.
- The lo-pass filter: cuts all frequencies above a specified cut-off point, which allows lower frequencies to pass through.
- Also known as a ‘sweep‘ filter. Allows you to select a frequency (FC), and then to boost or cut that frequency by certain amounts, usually ranging from -12dB to +12dB.
- These are identical to semi-parametric filters, but with an added control, called ‘Q’. The Q parameter selects the bandwidth of the filter around the selected frequency, and is usually set between a range of 0-10 (0 being the widest, 10 being the narrowest).
- These contain between 16-32 separate filters, evenly spaced throughout the audible frequency range. Each filter’s frequency and Q settings are usually set automatically by the unit and cannot be adjusted. You can control the amount of boosting or cutting for each filter.
- This device can be used to filter out specific frequencies during recording and mixing. They can also be used to compensate for the sound of a room – a certain room, because of it’s shape, might have a resonant frequency that is causing problems. A graphic EQ unit can tune into this frequency and cut it. This feature is also useful during live performance mixing, where a live venue is ‘tuned’ and certain resonant frequencies cut.
- Similar to a graphic EQ unit, but you can select the frequency you want to boost or cut. The Q range is usually very narrow as well. This helps you to focus in on certain frequencies to an even greater accuracy than on a graphic unit.
The equalizer is a great tool to use when you need to shape your recordings and mixes to enable the different sources to sit together in a mix. I definitely recommend taking the time to learn about the important frequencies of different instruments, and to learn how these frequencies can be affected by the use of EQ to create better mixes and productions.