Effects of hearing-aid dynamic range compression on spatial perception in a reverberant environment

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.

Preserving spatial perception in rooms using direct-sound driven dynamic range compression

“…The experimental setup and procedure were similar to the ones described in Hassager et al (2017). The experiments took place in a reverberant listening room designed in accordance with the IEC 268-13 (1985) standard.…”

“…Individual BRIRs were measured from the loudspeakers placed at the azimuth angles of 0 and 300 . The BRIR measurements were performed as described in Hassager et al (2017). The microphones were placed at the ear-canal entrances and were securely attached with strips of medical tape.…”

“…It was shown by Hassager et al (2017) that this approach provided the listener with an undistorted spatial perception. However, such idealized processing requires a priori knowledge of the dry source signals and the respective BRIRs, which limits the potential applicability of this type of processing to actual hearing-aid applications.…”

“…However, as demonstrated in Hassager et al (2017) both independent and linked fast-acting compression (with an attack and release time of 10 and 60 ms, respectively) can strongly distort the spatial perception of sounds in reverberant acoustic environments. Both compression strategies can lead to an increased diffusiveness of the perceived sound and broader, sometimes internalized ("in the head"), sound images as well as sound-image splits.…”

“…Only normalhearing listeners participated in the present study. The main goal was to evaluate the feasibility of the approach motivated by the results from Hassager et al (2017). To quantify the distortion of the spatial perception in the different conditions, the IC of the ear signals was used as an objective metric.…”