1. A method for recognizing a speaker, comprising the steps of: extracting features from one or more enrollment utterances to generate a target speaker model based on a sample covariance matrix generated from said extracted enrollment features; extracting features from one or more test utterances to generate a test utterance model based on a sample covariance matrix generated from said extracted test features; and computing a sphericity ratio to recognize said speaker, said sphericity ratio comparing said test utterance model to said target speaker model and to a background model.