by Karn Watcharasupat
Spatial audio quality is a highly multifaceted concept (see this for a very long list of things to consider). “Geometrical” components of spatial audio quality are perhaps the least subjective aspect of spatial audio quality to quantify, yet there have been very little attempt at dealing withit since BSS Eval came out almost 20(!) years ago.
Even the geometrical component of spatial audio quality is not trivial to quantify. We resorted to only considering the interchannel time differences (ITD) and interchannel level differences (ILD) of the test signal relative to a reference signal. With this, it is actually possible to construct a signal model to isolate _some_ of the spatial distortion. By using a combination of Weiner-style least-square optimization and good ol’ correlation maximization, we propose a signal decomposition method to isolate the spatial error, in terms of interchannel gain leakages and changes in relative delays, from a processed signal. These intermediates parameters can then be used as a diagnostic tool to identify the nature of the spatial distortion and to quantify the spatial quality impairment.