Preferred frequency response for two- and three-channel amplification systems.

The purpose of these investigations was to compare the preferred frequency-gain responses obtained from two- and three-channel amplification systems. The current experiments were limited to a linear system in which the crossover frequency dividing the channels was systematically varied. The subjects for the experiment were nine individuals with mild to moderately severe sensorineural hearing loss with various audiometric configurations. The subjects listened to continuous discourse, in noise, via a computer-controlled digital master hearing aid containing two real-time data acquisition processors. Initially, a modified simplex procedure was used to obtain preferred frequency-gain responses using several different crossover frequencies. A round-robin procedure was then conducted in which each preferred response from the simplex was compared with every other preferred response. The frequency-gain responses chosen most often for the two- and three-channel systems were compared. The results showed no significant differences between the preferred frequency-gain response for the two- versus the three-channel system. In addition, the preferred response chosen most often was not consistently observed at the same crossover frequency for all subjects, with the exception of those with steeply sloping hearing loss who chose 1,120 Hz as the first or second preference for the two-channel system. The round-robin results were rank-ordered according to the number of times each frequency-gain response was chosen. In general, subjects chose several frequency-gain responses at various crossover frequencies, which were not significantly different from each other statistically. The results of a final experiment suggested that physical similarities in the preferred responses chosen at the various crossover frequencies played a role in the rank-ordering of the preference judgments obtained in the original investigation.