A graphic equalizer (GEQ) is a popular equalizer apparatus which divides the frequency band of audio signals into a large number of frequency subbands or channels and which can vary the frequency characteristics at the respective channels, and thereby change the frequency characteristics over the entire band as desired. A graphic equalizer typically will adjust the energy levels of the audio data in one or more different frequency bands in order to change the characteristics of the audio data. For example, the equalizer may adjust the audio data to concentrate more of the audio data into the middle frequency range which is more perceptible to more people. An equalizer may also be used to add more audio energy to the lower frequency bands which will then provide more bass sounds. Speaker systems employ elaborate crossover network circuitry to divide the signal among drivers whose design and composition are suited to relatively uniform performance with a frequency range. Graphic equalizers are introduced into the reproduction system to correct the signal for the variable influence of the listening room in different frequency ranges and to further compensate for speaker deficiencies, again with the goal of uniform response to a signal of a given amplitude whose frequency is varied. A speaker system usually includes several speakers which each handles a different range of frequencies, such as bass, mid-range, and high frequencies. The boundaries of frequency response for each speaker define crossover points beyond which crossover filters (or crossovers) block out-of-bound signals. A frequency response equalizer permits a user to adjust an amplitude gain at a specified frequency without affecting other frequencies. Equalizers are typically implemented as a series or cascade of individual filters, each with an independently adjustable gain to give the overall system the desired frequency response. Graphic equalizers are banks of filters in which only the gain or attenuation of each filter may be adjusted, while the frequency response of an individual filter may not be adjusted. Parametric equalizers are banks of filters in which the center frequency, bandwidth or Q, and the expected gain or attenuation at the center frequency may all be adjusted. Graphic equalizers typically have a frequency response determining circuit for each narrow audio frequency band that includes an adjustable component, often a slide resistor, oriented vertically in such a way that the positions of the controls or knobs of a plurality of adjacent adjustable components for each separate frequency band gives a graphical representation of the overall frequency response of the equalizer. A graphic equalizer may permit a one-to-one correspondence between the position of each filter segment control and a graph of the desired equalizer level adjustment vs. frequency. Each filter segment has a fixed center frequency. This permits rapid and unambiguous filter adjustments with a minimum of ancillary test equipment. Graphic equalizers are useful for tailoring or shaping the frequency response of an audio system to compensate for shortcomings in one or more of the components, for peculiarities in the listening environment, or simply to suit someone's personal listening preferences.

Graphic equalizers comprise a useful audio processing device, often allowing a listener to compensate for differences in taste or acoustic surroundings as appropriate. Typically, a graphic equalizer comprises a plurality of filters that each have a variable gain/attenuation associated therewith. The center frequencies for the various filters are distributed across an overall bandwidth having a upper and lower boundary. Graphic equalizers have a fixed number of filters having fixed center frequencies and bandwidths and adjustable gains. The user is able to adjust these gains for the preferred listening experience. Usually these filters are designed to span the entire audio band. The user is provided the capability to adjust the gain of these filters to change the equalization characteristics of the audio system and thus the output sound. An audio graphic equalizer divides the audio spectrum into narrow frequency bands, typically ten or twelve bands. On the front panel of the equalizer are provided a series of slide controls, each of which can be moved up or down from a neutral center position to raise or lower the sound level for a particular frequency band. When all of the slide controls are so adjusted their relative positions on the front panel of the equalizer provides a graphic display representative of the overall frequency response of the equalizer over the entire audio spectrum, typically from 20 Hz to 20 kHz. An automated graphic equalizer has a plurality of channels having fixed center frequencies and fixed Qs (ratio of center frequency to bandwidth of the channel) that cover the entire audio band with filters. Graphic equalizers which allow for the separate adjustment of a plurality of audio subbands so that the audio frequency response of an entertainment device can be operator adjusted so as to suit the operator's personal preference have been available only as discrete add-on units to existing entertainment devices. Audio systems typically use a graphic equalizer which can freely change the frequency characteristic of a reproduced signal to create the desired reproduction sound field characteristic. Due to the recent development of the digital signal processing technology, a digital graphic equalizer which uses a digital filter becomes popular. The circuit functions of such a digital graphic equalizer are generally accomplished on a software basis using a digital signal processor (DSP). Audio equalizers available for use with personal computers generally have been of two types. One is in the form of a daughter card installed internally in the computer's case on a slot of the mother board and is controlled via software which provides a graphic display on the video monitor of the computer. The other known type is essentially a stand-alone graphic equalizer which is connected to the outputs of the computer sound card with audio cables.