JFA-based front ends for speaker recognition

We discuss the limitations of the i-vector representation of speech segments in speaker recognition and explain how Joint Factor Analysis (JFA) can serve as an alternative feature extractor in a variety of ways. Building on the work of Zhao and Dong, we implemented a variational Bayes treatment of JFA which accommodates adaptation of universal background models (UBMs) in a natural way. This allows us to experiment with several types of features for speaker recognition: speaker factors and diagonal factors in addition to i-vectors, extracted with and without UBM adaptation in each case. We found that, in text-independent speaker verification experiments on NIST data, extracting i-vectors with UBM adaptation led to a 10% reduction in equal error rates although performance did not improve consistently over the whole DET curve. We achieved a further 10% reduction (with a similar inconsistency) by using speaker factors extracted with UBM adaptation as features. In text-dependent speaker recognition experiments on RSR2015 data, we were able to achieve very good performance using a JFA model with diagonal factors but no speaker factors as a feature extractor. Contrary to standard practice, this JFA model was configured so as to model speakerphrase combinations (rather than speakers) and it was trained on utterances of very short duration (rather than whole recording sessions). We also present a variant of the length normalization trick inspired by uncertainty propagation which leads to substantial gains in performance over the whole DET curve.