Introduction and meaning:
Equalization is a process in which either active or passive electronic elements are used for fulfilling the purpose of altering the frequency response characteristics of any given system. Though the term, Equalization is used in under many contexts, it generally points towards amplitude equalization. But there are other significant types of equalization. They are time-delay and phase equalizations. Spatial directivity equalization is another type of equalization.
The devices used for equalization are known as equalizers.
Types of equalizers and their uses:
There are many kinds of equalizers. The peaking equalizer helps raise or lower a particular range of frequencies around a given central point in a specific bell shape. If controls to adjust bandwidth, center frequency and other aspects like gain are installed in a peaking equalizer then it becomes a parametric equalizer. The job of installing these controls falls to the designer. If he doesn’t install any control for bandwidth, then the equalizer is called a semi-parametric equalizer. A shelving-type equalizer will increase or generally reduce the gain of a large range of frequencies by a particular amount. A low shelf equalizer will have a significant effect on low frequencies and will have little or no effect whatsoever above a particular point. The high shelf equalizer functions in exactly the opposite way, having no effect on frequencies below a particular given point. This kind of variable equalization was first put to use by John Volkman who worked for the Radio Corporation of America in the 1920s.
Another important kind of equalizer is the Graphic equalizer. It consists of a battery of filters for boosting and cutting different frequency ranges of sound. The amount of filters varies with the application. An ordinary car stereo equalizer may contain a battery of filters controlling about 2 channels for adjusting the stereo sound easily. It might contain 5-10 filter bands. An equalizer for professional live sound reproduction will contain about 25-31 bands. This is necessary for quicker control of room modes and feedback tones. This kind of equalizer is called a 1/3-octave equalizer as the center frequency of each of the filters is positioned exactly one third of an octave away from their neighbors. Equalizers with half the amount of filters per octave are also seen in instances where comparatively lesser precision is required for general tone-shaping. These equalizers are known as 2/3-octave equalizers.