EQUALIZATION
Equalization sounds as though it was a process for making things equal, but actually it is how the tonal balance of sound is changed. Human hearing covers a frequency range of about 20 Hz to 20 kHz with the lower frequencies being called “bass” and the higher “treble”.
Please note that every equalizer is made slightly differently and the response curves may not exactly match those I am showing. Think of the following curves as being typical of the response of some common console equalizers.
The “frequency response” of an equalizer can be plotted on a graph such as this one:
The green line across the middle of this chart is the response of an equalizer which is set “flat” or doing nothing. There is no boost or cut of any sound.
Simple equalizers often have just two knobs marked Bass and Treble. Such an equalizer is often called a “tone control”. Here is the response of such a typical tone control with the Bass fully boosted and the Treble cut some:
Such a response will sound very “boomy” because of the large amount of bass boost, and a bit “dull” because of the reduction at the higher frequencies.
If the Treble control was turned about half way up with the Bass control set to zero, the response would look like this:
This would sound “bright”.
If the Bass control was turned half way down with the Treble control set to zero, the response would look like this:
The Bass and Treble controls in the above graphs are said to be “shelving” equalizers since in the Bass or Treble ranges they flatten out and look like a shelf the height of which is adjustable with the knob.
Often the channel equalizers on each input of a console will have 3 or 4 bands of equalization and not just two. These mid frequency controls produce a peak or dip in the response centered on some frequency. Here is a typical mid frequency equalizer set to boost 5 dB at 1 kHz:
Some mid frequency equalizers allow you to adjust the frequency at which they operate. Here is that same equalizer set of 600 Hz.
Some mid frequency equalizers not only allow you to adjust the level and frequency but also how wide a frequency range the equalizer effects. The above curves were made with a 1.5 octave width. Here is the same equalizer set for a cut of 6 dB and a width of 0.5 octave:
Finally here is the same equalizer set for a boost of only 3 dB, but with a bandwidth of 3 octaves:
While the amount of boost is not great, there is a broad range of frequencies effected.
Narrow equalization boosts tend to be more noticeable to the ear than narrow cuts. That is one reason the equalization controls on a typical mixer tend to not have very narrow frequency ranges. Another reason is that with only two to four equalization controls on a typical mixer input, letting each control effect a broader range of frequencies lets you do more with the limited number of controls.
The equalization controls on each mixer input are intended for use in modifying the sound from each input so they can better blend and produce the desired combined sound. As a result there are few hard and fast rules for adjusting console equalizers. Their adjustment is based on your musical judgment as the mix musician.
In later articles I will discuss the adjustment of equalizers in more detail and write about other uses for equalizers such as system EQ.
Ray A. Rayburn
Ray@K2Audio.com
http://www.K2Audio.com/
