15. The method of claim 14 wherein the tan h-based mapping operation comprises: collecting a set of confidence scores representing acceptance metrics from the first confidence classifier and a set of confidence scores representing acceptance metrics from the second confidence classifier, and learning a bias parameter and a scale parameter such that a a tan h of the confidence scores representing acceptance metrics from the first confidence classifier equals the bias parameter plus a product of the scale parameter and a tan h of the confidence scores representing acceptance metrics from the first confidence classifier.
14. The method of claim 9 wherein the mapping operation comprises: tan h-based mapping generating the mapped speech recognition confidence classifier score that equally or more accurately satisfies the recognition acceptance condition than the first speech recognition confidence classifier score.