Equalization – Types of Equalizers
Of all the various types of equalizer, these units offer the most flexibility because
their frequency selector control is continuously variable within the chosen bandwidth. They divide the total range into three or four overlapping bands and allow the engineer to deal with each band separately. Any frequency within each band can be selected for treatment, and all three or four bands can be modified simultaneously.
This added flexibility carries obvious advantages. Furthermore, some parametrics also possess a Q control for each band. This control addresses the immediately adjacent frequencies of any particular selection and is also called the bandwidth control.
For example, we can select a frequency of 6k and boost it 10dB. The Q control,
although continuously variable, can select a narrow, medium, or wide bandwidth
around our 6k selection. Whichever frequency is selected for equalization treatment, all similar Q bandwidths span an identical range either side of the selected frequency in terms of octaves.
These provide a visual display of the applied equalization curve via the positions of the sliders on the unit, which simulate the graphical curve. They’re available as software or hardware units. Graphic eq with a greater quantity of sliding controls can make more precise tonal adjustments than those with fewer sliders. Units typically have between five and 27 controls per channel. Each sliding potentiometer raises or lowers a specific frequency up to 12 or 16dB. Graphic equalizers do not possess a Q (bandwidth) control, but their individual bandwidths are usually quite narrow.
They can provide control over many frequencies at the same time. Hardware versions are generally found as pieces of outboard equipment rather than fitted into a console.
Notch filters are a rather more specific equalizing tool, capable of filtering out (or boosting) an extremely narrow bandwidth. A common use for notch filters is to eliminate the 60Hz hum which originates from AC power supplies when it is inadvertently being picked up by a cable or another piece of equipment. The notch
filter can be set to pinpoint a very thin bandwidth around 60Hz (possibly between 55 to 65Hz), and consequently very little effect will be noticed on the adjacent frequencies and the hum all but disappears.Notch filters also have practical applications for improving the sound of troublesome musical instruments. A common application is the removal of unwanted resonant rings from poorly-tuned drums.