Abstract
Fast-acting hearing-aid compression systems typically distort the auditory cues involved in the spatial perception of sounds in rooms by enhancing low-level reverberant energy portions of the sound relative to the direct sound. The present study investigated the benefit of a direct-sound driven compression system that adaptively selects appropriate time constants to preserve the listener's spatial impression. Specifically, fast-acting compression was maintained for time-frequency units dominated by the direct sound while the processing of the compressor was linearized for time-frequency units dominated by reverberation. This compression scheme was evaluated with normal-hearing listeners who indicated their perceived location and distribution of sound images in the horizontal plane for virtualized speech. The experimental results confirmed that both independent compression at each ear and linked compression across ears resulted in broader, sometimes internalized, sound images as well as image splits. In contrast, the linked direct-sound driven compression system provided the listeners with a spatial perception similar to that obtained with linear processing that served as the reference condition. The independent direct-sound driven compressor created a sense of movement of the sound between the two ears, suggesting that preserving the interaural level differences via linked compression is advantageous with the proposed direct-sound driven compression scheme.
Highlights
In everyday acoustic environments, the sound that reaches a listener’s ears contains the direct sound stemming from the different sound sources as well as reflections from obstacles in the surroundings
The classification stage in the direct-sound driven compressor was either based on the short-term signal-to-reverberant energy ratio (SRR) using a priori knowledge of the binaural room impulse responses (BRIRs) or on the blind classification method by Hazrati et al (2013)
This study presented a direct-sound driven compression scheme that applied fast-acting compression in T-F units dominated by the direct sound while linearizing the processing via longer time constants in T-F units dominated by reverberation
Summary
The sound that reaches a listener’s ears contains the direct sound stemming from the different sound sources as well as reflections from obstacles in the surroundings. 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. A dereverberation of the binaural room impulse responses (BRIRs) for each of the sound sources would be required to apply compression to the individual “dry” sound sources, followed by a convolution of the individual sound sources with the respective BRIRs to reintroduce and preserve the spatial chararcteristics of a given scene It was shown by Hassager et al (2017) that this approach provided the listener with an undistorted spatial perception. To quantify the distortion of the spatial perception in the different conditions, the IC of the ear signals was used as an objective metric
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