In this study, we transform the verification scores of a speaker recognition system in order to standardize the imposter score distribution, this facilitates setting of a speaker-independent threshold at desired False Alarm (FA) rates. Impostor score distributions are estimated using GMMs, and a univariate Gaussianization  transform (which is a monotonically increasing mapping) is applied on the scores. It is shown that if a monotonically increasing mapping is used, the Probability of correct detection for a given setting of the FA is maintained as before. Hence, the proposed technique performs distribution scaling without affecting the False Alarm to False Reject relationship of the original test statistic. The maximum (relative) mismatch between the obtained and desired False Alarm rates is less than 10% for a wide range of False Alarm rates. When compared to modeling the imposter score distributions using a single Gaussian (Z-norm case), the overall relative mismatch is reduced by an average of 30%. While the application focus is on speaker recognition, the proposed technique can be used for other binary speech classification tasks as well.
Bibliographic reference. Prakash, Vinod / Hansen, John H. L. (2007): "Score distribution scaling for speaker recognition", In INTERSPEECH-2007, 2029-2032.