Click here to purchase the entire book in PDF format. Graphic Equalizer Graphic equalizers are seen just about everywhere these days, primarily because they're intuitive to use. In fact, they are probably the most-used piece of signal processing equipment in recording. The name ``graphic equalizer'' comes from the fact that the device is made up of a number of filters with centre frequencies that are regularly spaced, each with a slider used for gain control. The result is that the arrangement of the sliders gives a graphic representation of the frequency response of the equalizer. The most common frequency resolutions available are one-octave, two-third-octave and one-third-octave, although resolutions as fine as one-twelveth-octave exist. The sliders on most graphic equalizers use ISO standardized band center frequencies (See Section 12.1). They almost always employ reciprocal peak/dip filters wired in parallel. As a result, when two adjacent bands are boosted, there remains a comparatively large dip between the two peaks. This proves to be a great disadvantage when attempting to boost a frequency between two center frequencies. Drastically excessive amounts of boost may be required at the band centers in order to properly adjust the desired frequency. This problem is eliminated in graphic EQ's using the much-less-common combining filters. In this system, the filter banks are wired in series, thus adjacent bands have a cumulative effect. Consequently, in order to boost a frequency between two center frequencies, the given filters need only be boosted a minimal amount to result in a higher-boosted mid-frequency. Virtually all graphic equalizers have fixed frequencies and a fixed Q. This makes them simple to use and quick to adjust, however they are generally a compromise. Although quite suitable for general purposes, in situations where a specific frequency or bandwidth adjustment is required, they will prove to be inaccurate.