Real-Time Simulation of Reduced Frequency Selectivity and Loudness Recruitment Using Level Dependent Gammachirp Filters
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A real-time system for simulating reduced frequency selectivity and loudness recruitment was implemented in the C programming language. The finished system is an executable program where a user can input a sound file and a list of hearing losses. As the program runs, a processed version of the input signal is played back. The processed signal includes the effects of either one or both the hearing impairments. The system, called a hearing loss simulator, is based on the dynamic compressive gammachirp filter bank. Each channel in the filter bank is signal dependent, meaning the filter characteristics are changed according to an estimate of the signal level. Reduced frequency selectivity was simulated by influencing the filter characteristics by a hearing loss value in addition to the signal level. This produced masking effects, and was able reduced the detail of spectral envelopes. Loudness recruitment was simulated by scaling each sample based on the signal level. This technique accounted for abnormal growth of loudness-level and elevated absolute thresholds. It made low sounds disappear while leaving loud sounds closer to their original level.