AN INVESTIGATION INTO LEARNING EFFECTIVE SPEAKER SUBSPACES FOR ROBUST UNSUPERVISED DNN ADAPTATION

Subspace methods are used for deep neural network (DNN)based acoustic model adaptation. These methods first construct a subspace and then perform the speaker adaptation as a point in the subspace. This paper aims to investigate the effectiveness of subspace methods for robust unsupervised adaptation. For the analysis, we compare two state-of-the-art subspace methods, namely, the singular value decomposition (SVD)-based bottleneck adaptation and the factorized hidden layer (FHL) adaptation. Both of these methods perform speaker adaptation as a linear combination of rank-1 bases. The main difference between the subspace construction is that FHL adaptation constructs a speaker subspace separate from the phoneme classification space while SVD-based bottleneck adaptation shares the same subspace for both the phoneme classification and the speaker adaptation. So far, no direct comparisons between these two methods are reported. In this work, we compare these two methods for their robustness to unsupervised adaptation on Aurora 4, AMI IHM and AMI SDM tasks. Our findings show that the FHL adaptation outperforms the SVD-based bottleneck adaptation especially in challenging conditions where the adaptation data is limited, or the quality of the adaptation alignments are low.