gms | German Medical Science

Some studies report that short, impulse-like noise signals with high sound pressure levels, such as slamming a door or rattle of dishes, are particularly uncomfortable for hearing aid users. Therefore, many hearing aids provide impulse (or transient) noise reduction that aims at reducing loud and short noise signals without impairing the desired signal, mostly speech.

In this work, we used anechoic recordings of 9 impulse noises [1] and presented them to 24 hearing-impaired with a hearing loss of type N3 according to IEC 60118-15 and 20 normal-hearing subjects via a loudspeaker in an audiological test room. All subjects rated how uncomfortable they experienced the signals on a nine-point scale from not uncomfortable to extremely uncomfortable. For the hearing-impaired subjects, six pairs of commercially available hearing aids of the five largest hearing aid manufacturers, released between 2017 to 2021, were selected for this study. Two hearing aid pairs belong to different brands of one manufacturer with different signal processing strategies. The hearing aids were fitted with real ear measurements (REMs) according to NAL-NL2. All were standard Behind-the-Ear hearing aids and coupled to the ear either through a custom ear mold or a foam earplug that both included a vent with a diameter of 1.4 mm. Moreover, individual uncomfortable loudness levels (UCLs) were measured with pure tones and used as fitting target for the output limiter using REMs and the EUHA MPO signal [2]. The hearing aid settings for all other features were left as suggested by the fitting software of the manufacturers for the audiogram of the subject. Only impulse noise reduction was deactivated or set to maximum effect. In each configuration, all 9 signals were rated 5 times by the subjects. All signals were rated without hearing aids and the hearing-impaired subjects also rated the signals while successively wearing all six hearing aids with and without activated impulse noise reduction. As a result, the subjective ratings of the hearing-impaired subjects with and without activated impulse noise reduction were compared to the ratings of the normal hearing test subjects. Moreover, the ratings were analyzed with respect to type of signal and type of hearing aid.