Equalization in the purest sense makes the sound equally strong in all frequencies, by boosting or cutting certain frequency components in a signal.
This effect was initially used to obtain a flat frequency response, a sound with no coloration. Of course in reality you don’t want the music that you play to be flat.
Cutting or boosting certain frequency bands is most commonly done when increasing/decreasing the bass and/or treble (i.e. the equalizer).
The player can change frequency bands thus changing output sound to suit their preferences. This is accomplished by using bandpass filters.
Each filter covers different frequencies without interfering with the other filters. Each filter has controllable gain which means the user can control the gain on each frequency covered.
The basic use of equalization is tone control. This simple system can be found on all stereo systems and, as mentioned above, controls the quality of the sound by controlling the bass and treble amount.
These controls control the so-called shelving filters (lowpass and highpass). As opposed to the common lowpass and highpass filters which completely remove a portion of the sound spectrum, shelving filters allow the user to cut or boost a certain portion.
For example, the lowpass filter will eliminate all the high frequencies while the shelving lowpass filter will simply allow you to boost or cut the high frequencies depending on the sound you are looking for.
Graphic equalizers take tone controls a step forward controlling a wide area of frequencies. These equalizers are composed of several filters each centered on a certain frequency and controlled by a slider.
Moving the slider up will boost the frequency it controls while sliding it down will cut the frequency.
Equalization is also used when there is more than one instrument and certain frequency ranges of instruments step on each other.
When you are doing this one thing that can help you a lot is to know the frequencies that correspond to the fundamentals of each musical pitch.
The violin pitch range is between 196 Hz and 3136 Hz so is unlikely to get some tonal changes if you try to equalize the violin part around 130 Hz.
Knowing these frequencies can also help when you are trying to get some unwanted pitches for example noise out of your sound.
On the other hand what you really want to know is how to use this information with the equalizer units. It’s very important not use too much equalization on your sound especially when you can’t use a professional equalizer.
These units have the ability to degrade the sound so it’s more important to try to play a clean music than to rely on the equalizer for this.
All equalizers sound different even with the same nominal settings, different models respond in different ways for the same input sound.
For example the difference between analogue and digital units is very obvious, the analogue work very well but they can cause great tonal modification, while on the other hand the digital units cause very small tonal changes when trying to boost the sound.
There are a lot of options if you’re looking for an equalizer. Before you choose your equalizer you should really gather some information about what’s out there. You do want to get the equalizer that best fits your needs.