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.
The authors acknowledge the financial support of the HEARing CRC, established and supported under the Cooperative Research Centres Program—an initiative of the Australian Government.
I. INTRODUCTION II. HIGHER-ORDER AMBISONICS A. Fourier-Bessel series expansion B. Decoding to a loudspeaker array C. Modified (max-r E) decoding D. Sound-field encoding with a microphone array III. METHODS A. Acoustic scene simulation 1. Room model 2. Rendering to auxiliary sound sources B. Sound field coding 1. HOA microphone array considerations C. Playback and sound-field synthesis 1. HOA reconstruction error 2. Loudspeaker array configuration 3. HOA system noise D. Directional HA microphone and SNR benefit IV. SIMULATION RESULTS A. Microphone array noise B. Anechoic virtual source reconstruction 1. HOA pressure errors 2. Directional HA-microphone HOA errors C. Reverberant virtual source reconstruction 1. HOA pressure errors 2. Directional HA-microphone HOA errors V. DISCUSSION A. HOA system noise B. HOA errors for anechoic source reconstruction 1. HOA pressure errors 2. Directional HA-microphone HOA errors C. HOA errors for reverberant source reconstruction 1. HOA pressure errors 2. Directional HA-microphone HOA errors VI. CONCLUSIONS