Estimating and Reproducing Ambience in Ambisonic Recordings

Spatial audio coding and reproduction methods are often based on the estimation of primary directional and secondary ambience components. This paper details a study into the estimation and subsequent reproduction of the ambient components found in ambisonic sound scenes. More specifically, two different ambience estimation approaches are investigated. The first estimates the ambient Ambisonic signals through a source-separation and spatial subtraction approach, and there-fore requires an estimate of both the number of sources and their directions. The second instead requires only the number of sources to be known, and employs a multi-channel Wiener filter (MWF) to obtain the estimated ambient signals. One approach for reproducing estimated ambient signals is through a signal processing chain of: a plane-wave decomposition, signal decor-relation, and subsequent spatialisation for the target playback setup. However, this reproduction approach may be sensitive to spatial and signal fidelity degradations incurred during the beamforming and decorrelation operations. Therefore, an optimal mixing alternative is proposed for this reproduction task, which achieves spatially incoherent rendering of ambience directly for the target playback setup; bypassing intermediate plane-wave decomposition and excessive decorrelation. Listening tests indicate improved perceived quality when using the proposed reproduction method in conjunction with both tested ambience estimation approaches.