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Features The variable-Q active filter sets used in the EQ-231 allow effective equalization with few problematic side effects. As Figure 1 illustrates, the filter characteristics vary with the amount of boost or cut used. At low control settings, the filter Q is very wide. As the control is boosted or cut, the filter Q narrows so that there is minimum interaction between adjacent frequency bands. Each of the 31 1/3-octave filters per channel provides 12 dB of boost or cut at ISO frequencies 20 th