Equalization Techniques

An equalizer is an audio device with multiple frequency controls for adjusting sound tone quality. There are many reasons for using an equalizer.

This article will look into a few of the common applications for the equalizer, including:

Correct problems in a recording

An equalizer can be used to compensate for deficiencies in a sound pickup or to reduce extraneous sounds, such as noise.

Remember that it is far better to get the recording right first time around, rather than trying to fix it in the mix. Equalization should not be used as a way out of a bad recording when mixing.

Some tips to consider during, and after a recording include:

  • Switch high pass filters on when needing to eliminate unwanted low rumbles, for example, from local traffic
eq techiques high pass filter
Fig 1. - High pass filter (1kHz)
  • Switch low pass filters on when needing to eliminate interference and high frequency noise, such as hiss
eq techiques low pass filter
Fig 2. - High pass filter (1kHz)
  • For bassy instruments, filter off any frequencies above 8 kHz, as they are generally not audible but can still induce extra noise
8kHz rolloff
Fig 3. - Filter away frequencies above 8kHz
  • Be aware of the proximity effect, especially when miking drum kits. If added bass energy becomes a problem, roll off some of the low frequencies
eq techiques lowpass sub
Fig 4. - Cut low frequencies to help eliminate the proximity effect

Improve instrument clarity

Equalization can help enhance an instruments sound.

Harmonic and Fundamental frequency rules

  • Boosting a sounds harmonics gives the impression of more presence and brightness
  • Decreasing  a sounds harmonics gives the impression of a dull, less dazzling sound
  • Boosting a sound around its first fundamental frequency will promote warmth and depth
  • Decreasing a sound around its fundamental frequency  will promote a colder, less powerful sound.
Learn about harmonics.

Muddiness and honk

The main problems in a mix are usually excess muddiness and honk.

Before beginning to equalize any instrument, it is important to listen to the sound in order to identify any nuance/unwanted frequencies. 

Muddiness normally comes from bass heavy instruments, such as the kick drum, bass guitar, and the lower end of the piano. The frequencies responsible are usually centered between 100-400 Hz. However, simply cutting these frequencies will make the sound thin as this area does contribute to the body and rhythm of a mix.

The best way to deal with muddiness is to scan the lower frequencies with a high Q setting and a moderate boost level of about 8dB. Once excess muddiness is found, cut the signal right down, and then slowly bring up the gain control until there is a good balance between body and muddiness.

Exercise caution when cutting frequencies and do not cut the same frequency on all of the sounds.

The idea is to fill up the audio spectrum and applying cut to several sounds in the same frequency area will just leave a hole in a mix. If too much bass is lost from the sound, try adding some moderate boost to the sub-bass region at around 60 Hz to compensate.

The honk area is focused between 500-3000 Hz and determines how honky and prominent an instrument is in the mix. Excess output at this range can sound cheap, boxy and can cause unwanted ear fatigue. If boosting in this area, be very cautious, especially on vocals. Human hearing is extremely sensitive at these frequencies with the slightest boost or cut resulting in a huge change in the sound.

If there are any irritating frequencies, sweep through the sound with a medium curve at about 10dB cut. Once the frequencies are located adjust the amount of cut as desired. It may be necessary to compensate for any cutting in this area by applying a small amount of boost around the 5-8 kHz area to liven up anything that may have been severely affected by the cutting. This will help to preserve the overall brightness.

When applying equalization, it is advisable to use large amounts of cut or boost initially. This helps give a better idea of the frequencies being affected. The human ear can quickly become used to an equalized sound, so quick successive bursts on the gain knob until the frequency sounds about right is best.

Create room and balance

The equalizer can be useful for creating space in the mix by balancing frequencies. If certain instruments occupy a similar frequency band they will end up masking each occur within that particular area of the audio spectrum, often resulting in a muddy sound.

balance frequencies

To allow elements to best fit together, there has to be some juggling of frequencies so that each instrument has its own predominant frequency range. For example, if a kick drum is heavy and powerful in the 80 Hz but getting muddied up by the bassline, attenuating the bassline around this frequency will free up valuable mix room allowing for the kick to shine through. The result being that the mix will sound more clear and distinct.