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Perception of internally generated noise in hearing amplification.

Noise generated within hearing aid amplifiers is distracting and, if the level is high enough, may interfere with speech communication. For hearing aid specification and fitting, it is useful to know the acoustic levels at which internal amplifier noise becomes audible and at which it becomes objectionable. This paper reports, for eight subjects with moderate hearing losses, the perceived levels at which internal noise became both audible and objectionable, using a test amplifier with no acoustic input. For comparison purposes, five normal-hearing subjects were also tested. Two noise sources were tested. The first was a broadband noise that was shaped only by the receiver, used to simulate output stage noise. The second was a broadband noise shaped by the target National Acoustics Laboratory-Revised (NAL-R) frequency response for each subject's hearing loss, used to simulate input stage noise. For both types of noise, the overall levels and spectra of the noise are reported for each subject. The relationship between 1/3-octave measurements of the noise and the audiometric configuration of the subjects is explored. The internal level at which the noise was perceived to be audible could be related to 1/3-octave measurements of the noise through the audiometric configuration of each subject's hearing loss. The results for the frequency-shaped input-generated noise and for the output-generated noise were similar.