1. A parameter determination apparatus, comprising: a processor configured to determine a similarity index between a reference neurogram and a patient neurogram; and a frequency band determiner configured to determine an optimal frequency band based on the similarity index between a reference neurogram and a patient neurogram, wherein the optimal frequency band is based on a rate of change of the similarity index as a function of the frequency band, and the optimal frequency band is used to calibrate a hearing device for a hearing loss patient.