Simulation of hearing impairment based on the Fourier time transformation

A signal processing system was designed to simulate hearing impairment for normal hearing listeners. Typical consequences of sensorineural hearing loss are an elevated threshold in quiet, abnormal growth of loudness (`recruitment´) and reduced spectral and temporal resolution. However, the just noticable difference (jnd) in intensity is unaffected. Based on an aurally adequate time-frequency representation, these effects can be simulated by intensity quantization and frequency dependent dynamic level expansion. The Fourier time transformation (FTT) was used for analysis of the time signal and the inverse FTT for resynthesis of the modified complex spectra. Input-output functions used for level expansion are calculated from the audiogram and a categorical loudness scaling procedure. Hearing experiments were carried out to find the appropriate quantization step and to simulate intensity jnd´s of normal and hearing impaired listeners. The proposed processing scheme will be used to improve the design and fitting of hearing aids