Multirate modeling of human ear frequency resolution for hearing aids

A real-time multirate filtering design project, as an application in digital hearing aids, has been developed. The motivation is that it allows nonuniform frequency resolution which automatically leads us to use different decimators for different frequency bandwidths. Therefore, a variation of the tree structured multirate multistage filter bank is exploited with six pairs of polyphase filters for decimation and six pairs for interpolation to achieve seven different frequency bandwidths, each for an octave. Such nonuniform systems are well-suited for the processing of sound signals, because of the decreasing resolution of the human ear at higher frequencies. For audiogram match, the frequency response of the decimation filter bank can be individually adjustable in each octave band. The other advantages of multirate processing provide for less computational and storage requirements as well as lower order filter design. Texas Instruments Evaluation Module (EVM), based on the fifth generation TI TMS320C50 digital signal processor, is used for implementation.