Minimising the effects of filter overlap in multiband signal/noise improvement systems

Multiband signal processing is used in complementary audio noise-reduction systems to overcome the effects of the wideband noise modulation that occurs during changes of gain. Because practicable filters with a finite cutoff rate must be used to define each signal band, changes in the relative gains of adjacent signal bands in the frequency spectrum give rise to distortion in the overall amplitude/frequency characteristic. This paper is concerned with methods of applying gain-dependent correction to the time constants of each filter. Computer optimisation techniques have been used to evaluate filter-parameter correction factors, enabling a linear frequency response to be retained for differences in gain between adjacent channels of up to 12 dB.