Simulation of Frequency Characteristics in Pathological Auditory Systems by Means of FIR Digital Filters

Abstract

Speech discrimination scores can be affccted by frequency characteristics of the auditory systems ie. pure tone audiograms of hearing impaired patients. This may be one of reasons why it is difficult to determine the site of lesion in the auditory pathway by speech audiometry.
In order to evaluate the effect of pure tone audiograms, the authors propose the application of a digital filter to simulate the abnormal frequency charactoristics of the ear in this paper. (1) The results obtained by digital filter were compared with those from the analog filter which has usually been applied. Digital filters are superior to analog ones at some points such as signal to noise ratio, flexibility of design and stability of frequency characteristics etc. (2) The effect of finite impulse response (FIR) digital filter was compared theoretically with that of the infinite impulse response (IIR) digital filter. It was concluded that the FIR digital filter was better than the other because any pure tone audiograms could be approximated by this filter with linear phase.
The FIR digital filter used in this experiment was designed by a window method, and filtered speed sounds were produced to simulate the abnormal speech perception of patients and presented to the normal hearing subjects. The results from this procedure were compared with those obtained from the patients. In conclusion, the FIR digital filter is useful to simulate the frequency characteristics of the auditory systems.