Multigrained modeling with pattern specific maximum likelihood transformations for text-independent speaker recognition

We present a transformation-based, multigrained data modeling technique in the context of text independent speaker recognition, aimed at mitigating difficulties caused by sparse training and test data. Both identification and verification are addressed, where we view the entire population as divided into the target population and its complement, which we refer to as the background population. First, we present our development of maximum likelihood transformation based recognition with diagonally constrained Gaussian mixture models and show its robustness to data scarcity with results on identification. Then for each target and background speaker, a multigrained model is constructed using the transformation based extension as a building block. The training data is labeled with an HMM based phone labeler. We then make use of a graduated phone class structure to train the speaker model at various levels of detail. This structure is a tree with the root node containing all the phones. Subsequent levels partition the phones into increasingly finer grained linguistic classes. This method affords the use of fine detail where possible, i.e., as reflected in the amount of training data distributed to each tree node. We demonstrate the effectiveness of the modeling with verification experiments in matched and mismatched conditions.