Abstract
This study investigated the effects of fast-acting hearing-aid compression on normal-hearing and hearing-impaired listeners' spatial perception in a reverberant environment. Three compression schemes-independent compression at each ear, linked compression between the two ears, and "spatially ideal" compression operating solely on the dry source signal-were considered using virtualized speech and noise bursts. Listeners indicated the location and extent of their perceived sound images on the horizontal plane. Linear processing was considered as the reference condition. The results showed that both independent and linked compression resulted in more diffuse and broader sound images as well as internalization and image splits, whereby more image splits were reported for the noise bursts than for speech. Only the spatially ideal compression provided the listeners with a spatial percept similar to that obtained with linear processing. The same general pattern was observed for both listener groups. An analysis of the interaural coherence and direct-to-reverberant ratio suggested that the spatial distortions associated with independent and linked compression resulted from enhanced reverberant energy. Thus, modifications of the relation between the direct and the reverberant sound should be avoided in amplification strategies that attempt to preserve the natural sound scene while restoring loudness cues.
Highlights
With the aim of preserving the naturally occurring ILDs, state-of-the-art bilaterally fitted hearing aids share the measured sound intensity information in one hearing aid with that in the other hearing aid via a wireless link
The upper left panel represents the responses for the linear processing, whereas the responses obtained with independent compression, linked compression, and spatially ideal compression are shown in the upper right, lower left, and lower right panels, respectively
To illustrate when a listener experienced a split in the sound image and, indicated more than one circle on the touch screen, only the circle the listener placed nearest to the loudspeaker was indicated in color, whereas the remaining locations were indicated in gray
Summary
With the aim of preserving the naturally occurring ILDs, state-of-the-art bilaterally fitted hearing aids share the measured sound intensity information in one hearing aid with that in the other hearing aid via a wireless link. The ear signal with the higher sound intensity in a given acoustic sound source scenario is typically chosen as the one providing the input to the level-dependent gain function in both (left-ear and right-ear) DRC systems (Korhonen et al, 2015). For hearing-impaired listeners with a symmetrical hearing loss, this shared processing, often referred to as “synchronization” or “link,” implies that the amplification provided by the two DRC systems is the same such that the intrinsic ILDs are preserved. For hearing-impaired listeners with an asymmetrical hearing loss with different prescribed DRC gain settings [i.e., gain levels in the linear region, CTs, and compression ratios (CRs)] for the left and right ear, the synchronization of the provided input level to the gain functions does not necessarily lead to a preservation of the intrinsic ILDs. It has been demonstrated that linked fast-acting DRC systems, as compared to independent DRC systems, can.
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