Modelling the alternative hypothesis for text-dependent speaker verification

This paper describes text-dependent speaker verification as a task involving four classes of trials depending on whether the target speaker or an impostor pronounces the expected pass-phrase or not. These four classes are used to reformulate the log-likelihood ratio traditionally used in text-independent speaker verification. Three formulations of the alternative hypothesis are considered, leading to three new expressions of the verification score. Experiments performed on the publicly available RSR2015 database show a significant improvement compared to existing baseline scores. A relative gain up to 61% in term of minimum cost is achieved when considering that the alternative hypothesis is the union of three sub-hypotheses corresponding to the three existing classes of impostures.