gain measurement from two methods of nal- nl2 and dslm[i/o], using two persian fricative consonants in coupler

background and aim: 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. methods: 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.  results: 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). conclusion: 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.