Cochlear Implant Filterbank Design and Optimization: A Simulation Study

Cochlear implants (CIs) are devices capable of restoring hearing function in profoundly-deaf patients to an acceptable degree of performance. An essential processing step in any cochlear implant is frequency analysis, which is usually performed via banks of filters. Here, we simulate and test the suitability of different filters and filterbank architectures for CIs with respect to their performance in speech intelligibility. Four different filters were implemented in an established model of CI hearing, the tone-excited vocoder, namely: GTF (Gammatone Filter), DAPGF (Differentiated All-Pole GTF), OZGF (One-Zero GTF) and BUTF (Butterworth). Three filterbank parameters, the filter order ( N), the filter quality factor ( Q) and the number of channels ( Ch), and their combinations were tested using objective and subjective metrics. Simulation results show that all filters tested are suitable for CI implementation, but that the choice of Q and N parameter values is crucial. For most conditions, optimal ( N,Q) combinations were within few units away from the combination (2, 4).