Abstract: An audio frequency filter for a mixing console equalizer typically has a manual frequency control for setting its operating frequency range, and a manual gain control for controlling the gain of the filter independently of the set frequency range. The present filter further provides gain adjustment means for automatically adjusting the gain of the filter in dependence on the position of said operating frequency range relative to a reference frequency that lies intermediate the lower and upper ends of the audio frequency spectrum, the gain adjustment means being such that the filter gain is greater the further said operating frequency range is moved away from said reference frequency towards a said end of the audio spectrum. As a result, signal frequencies at the extreme of the audio spectrum are automatically boosted.