Equalization

In audio processing, equalization is the process of modifying the frequency envelope of a sound. Strictly, and etomogically, it means to correct for the frequency response of another audio device. For example, a particular microphone might be more sensitive to low frequency sounds than to high frequency sounds, so an equaliser would be used to increase the volume of the higher frequencies (boost), and reduce the volume of the low frequency sounds (cut).

In practice, there is a degree of aesthetics involved, rather than purely technical considerations. Additionally, using a bank of filters for an effect is sometimes referred to as equalization, even though it strictly isn't. One of the most direct uses of equalization is at a live event, where there are microphones and speakers operating simultaneously. An equalizer is used to ensure that there are no frequency bands where there is a round trip gain of greater than 1, as these are heard as audible feedback. Those frequencys are cut at the equalizer to prevent this.

An equalizer is simply a device that allows for a frequency dependent gain. The most common type is a bank of band-pass filters, with a gain control for each band independently. Normally, these bands are tight enough to give at least 3dB or 6dB maxium effect for neighbouring bands, and cover the range from around 20Hz to 20kHz (which is approximately the range of human hearing). A simple equalizer might have bands at 20Hz, 200Hz, 2kHz and 20kHz, and might be referred to as a 4 band equalizer. Typical equalizer for live microphone work might have as many as 24 or 32 bands. See also: High-pass filter and Low-pass filter.