Analysis on the timbre of Ambisonics recording by circular and spherical microphone array using a binaural loudness model

Ambisonics are a series of flexible sound reproduction systems that decompose and reconstruct sound field by each order approximation of spatial harmonics decomposition. Circular or spherical microphone array has been used for Ambisonics recording. For an array with given radius as well as given number and configuration of microphones, the spatial harmonics signals up to certain temporal frequency and certain order can be derived from the array outputs with appropriate accuracy. When the temporal frequency exceeds the given limitation of array, however, spatial aliasing occurs in the derived spatial harmonics signals. Spatial aliasing in recording causes error in reconstructed sound field, which inevitably change the timbre in reproduction. The present work analyzes the timbre in Ambisonics recording by rigid circular and spherical microphone array. The binaural loudness level spectra are used as a criterion to evaluate the timbre in reproduction. The results indicate that, array recording influences little on the binaural loudness level spectra and thus timbre in final reconstructed sound field providing that the high-frequency limit of microphone array exceeds that of sound field reconstruction. Increasing number of microphones extends the high-frequency limit of array and thus improves the timbre.