Gain measurement from two methods of NAL- NAL2 and DSLm[i/o], using two Persian fricative consonants in coupler

As the most perceived and articulated errors of hearing aid users occur in high frequency speech phonemes, this study aimed to find a way to amplify and reconstruct the errors. Thus, the study first prepared a recorded form of two Persian fricative consonants as stimulus; then, the rate of the prescribed gain of the two methods of National Acoustic Laboratories-Nonlinear 2 (NAL-NL2) and the Desired Sensation Level Multistage Input/Output (DSLm[i/o]) were compared. This study was performed using eight programmed hearing aids for severe sensorineural hearing loss in three configurations: flat, raising, and sloping. After fitting the hearing aids upon the NAL-NL2 and DSLm[i/o] methods, the rate of their gain for the consonants of /s/ and /f/, using Affinity 2.0 analyzer, was determined in 2 cc coupler at the three different levels. In the flat and raising audiograms, the prescribed gain of DSLm[i/o] for the two consonants in all three speakers and intensity level was more than NAL-NL2 (p<0.05). In the sloping audiogram, the significance of the difference of prescribed gain of these methods disappeared; however, the DSL m[i/o] in the low frequency area was higher than NAL-NL2 (p<0.001). The average prescribed gain of methods in the three frequency regions for the two consonants is different, and the prescribed gain of DSLm[i/o] in all frequencies, especially in the low frequency areas, is higher than NAL-NL2.