Audio Post 3: Equalizers

Posted by bsteel on
Monday, March 3rd, 2008 at 3:29 am

Equalizers

An equalizer (EQ) is used to boost or cut the volume of certain frequencies. Most equalizers have multiple bands, which enables the user to boost or cut volume across multiple frequencies, or bands. An equalizer that contains high, mid and low frequency controls is referred to as a three band EQ. Equalizers are used to shape sound of recorded content, correct poorly recorded audio, create a new sound out of an existing sound, and to blend multiple instruments into a well-balanced audio mix. It is highly important to monitor your audio on high quality flat (as in no volume boosts or cuts between 20 Hz to 20 kHz) speakers or headphones while working with EQ. I tend to use EQ sparingly unless I am attempting to salvage poorly recorded audio.

There are several types of equalizers the most common EQs you will see in most video editing software are: Graphic EQs, Parametric EQs and Shelving EQs. These three types of EQ are important to know, because they are common to video/audio production software, as well as recording studios or post houses.

Graphic Equalizers provide multiple volume boost/cut controls for a wide range of pre-selected frequencies. The graphic EQ is easily distinguished by its controls, which are typically a series of sliders that are physically lined up next to each other, providing a graphic representation of the overall EQ curve.

Parametric Equalizers allow the user to choose which frequencies they wish to boost or cut. Parametric EQs also enable the user to choose how wide or narrow they wish to cut each frequency with the ‘Q’ button. The ‘Q’ button distinguishes a full parametric EQ from a semi-parametric EQ. Both full and semi-parametric EQs are fully sweepable, meaning the user can sweep a boost/cut across the entire frequency spectrum in order to find the particular frequency they wish to attenuate.

Shelving Equalizers provide a single control for boost/cut at a predetermined high or low frequency. The user will typically boost a fixed frequency between 80Hz and 100Hz on the low end and 10kHz to 12kHz on the high end. Shelving equalizers not only boost/cut the fundamental or predetermined frequency but additional frequencies above and below the select frequency.

Below is a chart listing both the fundamental and harmonic resonating frequencies of a bass, tenor, alto and soprano voice. The fundamental frequency is the lowest frequency of the sound wave and a harmonic frequency is an overtone frequency, which is a multiple of the fundamental frequency. In laymen terms this chart demonstrates all the resonating frequencies of the voice based upon tonal qualities (e.g. bass, tenor, alto, soprano). This chart will help you to determine which frequencies to boost/cut in order to achieve a desired sound. For example, to add warmth and fullness boost the lower end of the fundamental frequency; cut the fundamental if the sound is too ‘bassy’ or ‘tubby’, and to add presence and clarity boost the harmonic frequencies; remove the harmonics if the sound is too ‘sizzly.’

-Brian Steel, Director, Spielberg Group

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