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Microphone Month 5

Constant Q

On many equalizers changing the gain of a frequency band also changes the Q, which effects the slope of the EQ curve and how many adjacent frequencies are effected to what degree. This is also the normal way for a simple filter design to work. Some manufacturers employ what they call constant Q designs with the idea that the equalizer behaves in a more predictable fashion as gain changes are made at various frequencies. The Q of an equalizer is defined as the center frequency divided by the half power bandwidth. On a 1/3 octave graphic equalizer, for example, the half power point at 1 kHz is 232 Hz wide. The Q is thus 1000/232 or 4.31. If the half power bandwidth of this EQ remains 232 Hz wide throughout its cut and boost range it can be said to be a Constant Q equalizer. Engineers debate whether this is really useful and whether it sounds as good as more conventional designs.

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