Background noise reproduction using spherical microphone array measurements

Background noise reproduction for the evaluation of telecommunication devices, such as a mobile phone, was investigated using the measurement of spherical microphone arrays. Two techniques, i.e. binaural synthesis using headphones and higher-order Ambisonics, were evaluated for the study. Binaural synthesis was made by performing spherical beamforming, and subsequently taking head-related transfer functions (HRTFs) into account. Higher-order Ambisonics was achieved by decomposing the measured/simulated sound fields into a series of spherical harmonic functions (encoding) and deriving loudspeaker signals based on the geometry of a loudspeaker setup (decoding). Both techniques require the same type of recordings using a spherical microphone array. They were compared with existing techniques, such as the four-loudspeaker playback in ETSI EG 202 396-1. The investigation provides practical examples for objective and subjective assessment of background noise, and reveals the advantages of the techniques for the evaluation of devices under test in the presence of background noise.