  Deep speaker embedding represents the state-of-the-art technique for speaker
recognition. A key problem with this approach is that the resulting deep
speaker vectors tend to be irregularly distributed. In previous research, we
proposed a deep normalization approach based on a new discriminative
normalization flow (DNF) model, by which the distributions of individual
speakers are arguably transformed to homogeneous Gaussians. This normalization
was demonstrated to be effective, but despite this remarkable success, we
empirically found that the latent codes produced by the DNF model are generally
neither homogeneous nor Gaussian, although the model has assumed so. In this
paper, we argue that this problem is largely attributed to the
maximum-likelihood (ML) training criterion of the DNF model, which aims to
maximize the likelihood of the observations but not necessarily improve the
Gaussianality of the latent codes. We therefore propose a new Maximum
Gaussianality (MG) training approach that directly maximizes the Gaussianality
of the latent codes. Our experiments on two data sets, SITW and CNCeleb,
demonstrate that our new MG training approach can deliver much better
performance than the previous ML training, and exhibits improved domain
generalizability, particularly with regard to cosine scoring.
