Area code, country code, and time difference information system and its field trial

This paper describes an ASR system which responds to customer inquiries over a telephone network. Customer inquiries on area codes, country codes and time differences are one of the most popular items in information service of international telecommunication. This system called ACTIS (Area code, Country code and Time difference Information System) responds to these inquiries. ACTIS recognizes Japanese continuous speech and vocabulary including the names of 299 countries and 721 major cities throughout the world. We report on several technical features of the system including (1) new acoustic models using additional acoustic parameters, that is, acceleration of MFCC parameters and a log energy for increasing the recognition rate, (2) CMS (cepstrum mean subtraction) with compensation by recognition results for normalizing various channel characteristics and real-time operation, and (3) robust speech detection and out-of-vocabulary word detection for improving robustness to ambient noise, irrelevant sound and out-of-vocabulary words, along with their effects on computer simulation. We also report on results of field trial at KDD and a subjective assessment by users.