Equalizers are a very common tool in audio production. In essence they allow us to adjust the tone of an instrument or voice. The most basic equalizers can be found on a home or car stereo, they are commonly known as the bass and treble controls.
Equalizers can be used for correction of the tonal response caused by the recording process or for enhancement. An example of correction could be taming the high frequencies on a vocal recording that was recorded using a very bright sounding microphone. An example of enhancement could be adding some extra bass to a kick drum to make it sound more powerful.
Equalizers can be both analogue and digital and can also be known as graphic equalizers and parametric equalizers. Graphic equalizers are not commonly used in actual music production but are commonly found in use within PA systems in night clubs. They are fast and effective to use in this situation. In a music recording or mixing studio you will mainly find parametric equalizers which are more effective at shaping an instrument in a useful way.
Types of EQ curve :
The most complex EQ curve is known as a parametric bell eq. So called because there are three parameters to be adjusted.
Frequency - The chosen frequency to be adjusted i.e. 50Hz, 1kHz, 10kHz.
Gain - Amount of gain or cut applied in dB (decibels)
Bandwidth or Q - Width of the bell shape (range of frequencies either side of the centre frequancy that will be boosted or attenuated)
A shelf eq differs from a parametric bell in that it effects only frequencies above or below it’s frequency selection. Therefore it often has only 2 parameters.
Frequency - frequency at which shelf works at.
Gain - amount of gain or cut applied.
Shelf equalizer curves are very good for cutting or boosting overall bass or general high freqencies above (high shelf) or below (low shelf) a chosen frequency.
High and low pass filters
High and low pass filters are very specific and useful. They have 2 controls and work by cutting frequencies below or above the cut off frequency. The controls are as follows:
Frequency - determines the frequency where filtering will occur. A high pass filter will cut frequencies below the frequency setting. A low pass filter will cut above the frequency setting.
dB per octave - determines how steep the filters action is. i.e. 6dB per octave is a gentle filter slope and 32dB per octave is a steep filter slope.
A high pass filter can be used to reduce the rumble (or vocal pops) or very low frequency energy in a signal and a low pass filter can attenuate the very high frequencies in a signal.
Practice makes perfect
When learning how to use eq it is best to experiment with some sounds sources such as a vocal recording or a kick drum. This way you can listen to how the sound changes as you adjust the controls. I recommend some fairly extreme settings initially (try gains or cuts of 6-8dB) as this will make it easier to get used to the changes in sound when you are starting. As time moves on you will improve your hand/ear co cordination and will be making effective eq decisions within a short period of time.
Barry Gardner is the chief engineer at SafeandSound Mastering. You can visit the site on this page: http://www.masteringmastering.co.uk/