Apparatus for and method of filtering in an digital hearing aid, including an application specific integrated circuit and a programmable digital signal processor

An apparatus for use in a digital hearing aid, the apparatus comprising a dedicated application specific integrated circuit and a programmable digital signal processor, wherein the dedicated application specific integrated circuit and the digital signal processor are partitioned from one another, and wherein the dedicated application specific integrated circuit comprises:

• an oversampled filterbank for filtering an information signal, the filterbank structure comprising a filter means defining a filter bandwidth, said filter means filtering said information signal and separating said information signal into a plurality of frequency band signals, each representing one of a plurality of uniformly spaced frequency bands within said filter bandwidth, said frequency bands being stacked in one of an even and an odd manner and said frequency bands at least slightly overlapping such that the summation of the unmodified frequency band responses of the plurality of said frequency bands sums to a function within a predetermined passband ripple over said filter bandwidth, wherein the filter means includes a selection input enabling at least one of the following to be selected:
• i) the number of frequency band signals
• ii) the bandwidth of said frequency bands
• iii) selection of stacking of said frequency bands in one of an even and an odd manner
• iv) an oversampling factor by which said frequency bands are sampled above the theoretical minimum of critical sampling
• a programmable digital processor;
• a multiplication means connected to the programmable digital signal processor and to the application specific integrated circuit wherein the multiplication means multiplies each band by a desired gain, and wherein the gain for each band is controlled by the programmable digital signal processor;
• and
• a connection between the dedicated application specific integrated circuit and the digital signal processor, by which the programmable digital signal processor adjusts the selection inputs of said oversampled filterbank.