Objective analysis of ambisonics for hearing aid applications: Effect of listener's head, room reverberation, and directional microphones

Abstract

Recently, an increased interest has been demonstrated in evaluating hearing aids (HAs) inside controlled, but at the same time, realistic sound environments. A promising candidate that employs loudspeakers for realizing such sound environments is the listener-centered method of higher-order ambisonics (HOA). Although the accuracy of HOA has been widely studied, it remains unclear to what extent the results can be generalized when (1) a listener wearing HAs that may feature multi-microphone directional algorithms is considered inside the reconstructed sound field and (2) reverberant scenes are recorded and reconstructed. For the purpose of objectively validating HOA for listening tests involving HAs, a framework was developed to simulate the entire path of sounds presented in a modeled room, recorded by a HOA microphone array, decoded to a loudspeaker array, and finally received at the ears and HA microphones of a dummy listener fitted with HAs. Reproduction errors at the ear signals and at the output of a cardioid HA microphone were analyzed for different anechoic and reverberant scenes. It was found that the diffuse reverberation reduces the considered time-averaged HOA reconstruction errors which, depending on the considered application, suggests that reverberation can increase the usable frequency range of a HOA system.

Spatial Cues Provided by Sound Improve Postural Stabilization: Evidence of a Spatial Auditory Map?

“…Once the signal is decoded, the 42 loudspeakers re-synthesize the whole auditory scene at the center of the sphere. At the 4th order, for an area including an average head of the listener (radius r 0 = 9 cm), the frequency cutoff of the ambisonics system is f c = 2, 426 Hz (Oreinos and Buchholz, 2015). …”

Validation of a Virtual Sound Environment System for Testing Hearing Aids

“…Another study, using a similar system, tested speech intelligibility in a 'complex' cafeteria environment with multiple talkers, and in a 'standard' anechoic environment [17]. Finally, two very recent simulation studies investigated the applicability of multichannel loudspeaker-based reproduction chains for testing HAs [18,19]. However, in all above studies, the VSE systems were evaluated either by comparing theoretical quantities, or room acoustical measures between the VSE and the underlying ODEON simulation, or by comparing results of behavioural measurements obtained inside the system.…”

Evaluation of Loudspeaker-Based Virtual Sound Environments for Testing Directional Hearing Aids

“…This method does not require the time-consuming development of room acoustic models and can easily reproduce highly complex scenes with moving sound sources. However, HOA gives rise to spectral, temporal, and spatial artifacts, limiting the usable frequency range of the system (Oreinos and Buchholz, 2015). More specifically, the HOA method (a) has a limited spectral and spatial accuracy, determined by the size, geometry, and number of sensors/sources of both the employed microphone and loudspeaker array; (b) exhibits a sweet spot with a size that diminishes with frequency; and (c) is affected by amplified microphone noise induced during the HOA encoding process of the recorded signals.…”

“…The participants were individually fitted with a pair of experimental HAs on which two example signal processing schemes were implemented: a static directional cardioid hearing aid microphone (CRD; Kates, 2008) and an adaptive bilateral hearing aid beamformer (BBF) (Mejia et al, 2007;Mejia and Dillon, 2010). These schemes were chosen since, due to their directional processing, they were expected to be highly sensitive to any potential artifacts created by the two VSEs (Oreinos and Buchholz, 2015). Similar to the study by Best, Mejia, et al (2015), two different listening tests were conducted to measure the performance of the CRD as well as the additional benefit provided by the BBF processing: a speech intelligibility test and an acceptable noise level (ANL) test.…”