Comparison of the Effects of One and Two Knee Points in Compression Systems on the Score of the ANL Test in People with Sensory Neural Hearing Loss

One of the main purposes of hearing aid fitting for a patient with sensorineural hearing loss is to improve speech intelligibility in noise. Many parameters can influence this goal among which is compression. Compression systems typically compress the amplitude of sounds in order to improve speech intelligibility. One of the factors which determine the function of compression is its knee point. The present study was carried out to comprehensively investigate the effects of using one knee point compared to two knee points in compression systems on the score of the Acceptable Noise Level test in individuals with sensorineural hearing loss. A total of 15 patients suffering from sensorineural hearing loss participated in the study. All participants were fitted with Siemens Motion P 3mi hearing aids. The Most Comfortable Level and the Background Noise Level were measured and the Acceptable Noise Level was tested in three conditions, i.e. unreinforced, reinforced with one knee point, and with two knee point. Time constants (fast) and channel numbers (N=6) remained fixed. The results of the present study showed that there was not any significant differences between the reinforced with one knee and two knee points conditions and the unreinforced and mean acceptance level of noise in reinforced conditions. No significant association was found between mean ANL and the average of hearing thresholds in unreinforced and reinforced conditions with one and two knee points. According to the findings, it was not possible to determine the Acceptable Noise Level based only on the measured hearing thresholds. Also, increasing the number of knee points from one to two had no major effects on the score of the Acceptable Noise Level test, and one knee point might be enough to understand Speech in noise. Therefore, it seems that there is no need to increase the number of knee points in the compression systems.