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Abstract

Frequency characteristic shaping circuitry having a plurality of bandpass filters to which an audio signal is supplied and a plurality of variable gain attenuators individually associated with the bandpass filters. The output signals of the variable gain attenuators are supplied to a pair of summing circuits, one providing a sum of the attenuator output signals and the other providing an inverted version of the sum of the attenuator output signals. The sum of the attenuator output signals and the inverted version of the sum of the attenuator output signals are combined in a final summing circuit. In another aspect of the present invention, each bandpass filter has a second variable gain attenuator and the output signals of these attenuators are supplied to another pair of summing circuits, one providing a sum of these attenuator output signals and the other providing an inverted version of the sum of these attenuator output signals. The sum of these attenuator output signals and the inverted version of the sum of these attenuator output signals are combined in a another final summing circuit. The outputs of the two final summing circuits are sampled over variable periods of time determined by the loudness level of the audio signal supplied to the bandpass filters.

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First Claim