This guest post comes from Barry Gardner, mastering engineer at Safe And Sound online mastering.
Equalization is an incredibly powerful tool used in virtually every area of audio production including music recording and mixing. A lot of people initially feel equalization is a complex process but I would like to explain it as simply as possible but embellished with enough technical information to make it useful and valuable. At it’s most basic implementation an equalizer could be described as a tone control such as that on a hi fi amplifier. On an amplifier there are just 2 tone controls, bass and treble, as you turn the knob in either direction you either get an increase or decrease in the amount of bass or treble in the music, this is known as altering the tone.
When thinking of eq it is useful to imagine a horizontal line with the audible audio spectrum running from low frequencies (left) to high (right). Adult humans can hear from around 25Hz to around 20kHz (best case scenario). An equalizer allows specific frequencies of the spectrum to be focused upon and amplified or attenuated (reduced).