Comparison of the CAM2 and NAL-NL2 hearing aid fitting methods

To compare preference judgments for sounds processed via a simulated five-channel compression hearing aid with gains and compression ratios selected according to two recently introduced fitting methods, CAMEQ2-HF (hereafter named CAM2) and NAL-NL2.

There were 15 participants with sloping sensorineural hearing loss. They had mild losses, typical of people who might be candidates for wide-bandwidth hearing aids. Within a given trial, the same segment of sound was presented twice in succession to one ear, once with CAM2 settings and once with NAL-NL2 settings, in random order. The participant had to indicate which one was preferred and by how much. Judgments of overall sound quality were obtained for female and male speech in quiet and for four types of music (classical, jazz, a man singing, and percussion). Judgments of speech clarity were obtained for female and male speech in speech-shaped noise, female speech in a male-talker background, and male speech in a female-talker background. Factors investigated included compression speed (slow or fast) and input sound level (50, 65, or 80 dB SPL).

The pattern of the results was reasonably consistent across participants, but the magnitude of the effects was small. For judgments of overall sound quality, nine participants preferred CAM2 relative to NAL-NL2, and the remainder showed no clear preference. There was a significant overall preference for CAM2. The preference for CAM2 over NAL-NL2 in overall sound quality was present for all types of stimuli, both compression speeds, and all three levels. For judgments of the clarity of speech in noise, five participants preferred CAM2 over NAL-NL2, one showed the opposite preference, and the remainder showed no clear preference. There was a significant overall preference for CAM2. The preference for CAM2 over NAL-NL2 in the context of clarity of speech in noise was present for all types of stimuli, both compression speeds, and all three levels. For judgments of the clarity of speech in a background talker, CAM2 was significantly preferred overall relative to NAL-NL2, but the effect was very small.

For participants with mild sloping hearing loss, a simulated hearing aid unilaterally fitted using CAM2 was preferred over the same aid fitted using NAL-NL2 for overall sound quality and the clarity of speech in noise. Preferences differed only very slightly for the clarity of speech in a background talker. Further work is needed to establish whether similar preferences would be found in everyday life.