A method of making a speech recognition model database is disclosed. The database is formed based on a training string utterance signal and a plurality of sets of current speech recognition models. The sets of current speech recognition models may include acoustic models, language models, and other knowledge sources. In accordance with an illustrative embodiment of the invention, a set of confusable string models is generated, each confusable string model comprising speech recognition models from two or more sets of speech recognition models (such as acoustic and language models). A first scoring signal is generated based on the training string utterance signal and a string model for that utterance, wherein the string model for the utterance comprises speech recognition models from two or more sets of speech recognition models. One or more second scoring signals are also generated, wherein a second scoring signal is based on the training string utterance signal and a confusable string model. A misrecognition signal is generated based on the first scoring signal and the one or more second scoring signals. Current speech recognition models are modified, based on the misrecognition signal to increase the probability that a correct string model will have a rank order higher than other confusable string models. The confusable string models comprise N-best word string models. The first recognizer scoring signal reflects a measure of similarity between the training string utterance signal and the string model for that utterance. The second recognizer scoring signal reflects a measure of similarity between the training string utterance signal and a confusable string model. The misrecognition signal reflects a difference of the first scoring signal and a combination of one or more second scoring signals. The modification of current speech recognition models is accomplished by generating a recognition model modification signal according to a gradient of a function, which function reflects a recognizer score of a training string utterance based on a string model for that utterance and one or more recognizer scores of the training string utterance based on one or more confusable string models. <IMAGE>
Minimum error rate training of combined string models