![]() Three characteristics of distortion in hearing aids modify the sound delivered to the user: This implies that good sound quality is as equally important and desired by listeners with a hearing impairment as it is for listeners with normal hearing. Punch (1978) has shown that listeners with mild to moderate sensorineural hearing losses retain the same ability to make distinctions in sound quality judgments as listeners with normal hearing. Gabrielsson and Sjogren (1979b) have shown that overall perceived sound quality is important to users when selecting a hearing aid. It is known that highly distorted speech in quiet can remain intelligible ( Licklider, 1946) however, as dispensers often experience, intelligibility is not the only measure of whether or not a user will accept and wear hearing aids. The practical problem for the listener is the type of distortion that is present and the level that is acceptable or tolerable in hearing aids before the distortion becomes disruptive to speech intelligibility and sound quality. If they are large, they can be so disruptive to the listener that the desired sound becomes irritating or even incomprehensible.Īll audio systems inevitably contain some amount of distortion. If these added elements are small compared to the overall signal level, they may effectively cause no interference at all. These undesired components may interfere to some degree or other with the reception of sound by the listener. ![]() When distortion occurs, hearing aids produce undesired elements at the output through the interaction of the processed signal with some internal non-linear mechanism. The intention of this issue is to explain why distortion occurs in some hearing aids to explain how distortion is measured to summarize what can be done to prevent distortion and to summarize the perception of distortion by the hearing aid wearer.ĭistortion in hearing aids can be broadly defined as the generation of undesired audible components that are present in the output, but which are not present in the input. ![]() The topic of distortion is the subject of this issue of Trends in Amplification. This is a subtle way of saying that, among other things, well-fitted hearing aids should not distort the desired sound. This indicates that it is important that the hearing aids produce no alteration of the signal other than that which the fitter intends. The third guideline- do no harm-is less obvious. ![]() The second ensures that discomfort level is not exceeded, so that the user does not wince or remove the hearing aids when loud sounds are present. The first is to present sounds above the user's threshold of hearing in order to create an acoustic environment with the maximum amount of audible speech cues. The first two of these three guidelines are obvious. Do no harm so that the amplified signal is not unintentionally or undesirably altered by the hearing aid. ![]()
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