Robustness improvements in continuously spelled names over the telephone

A speaker-independent speech recognizer for continuously spelled names, implemented for a switchboard call-routing task, is analyzed for sources of error. Results indicate most errors are due to extraneous speech and end-point detection errors. Strategies are proposed for improving the robustness of recognition, including tolerance for speech with pauses, and a letter-spotting strategy to handle extraneous speech. Experimental results on laboratory data indicate that with the letter-spotting method, name retrieval error rate is reduced on noisy signals or signals with extraneous speech 60.1%, while it is increased on clean signals from 4.5% to 5.5%. On data collected during a telephone field trial, name retrieval error is reduced 54.1% in offline tests by introducing the letter-spotting algorithm