Bell Labs connected digit databases for telephone speech recognition

We describe Bell Labs connected digits databases (BLCD), which were collected over the landline telephone networks. The BLCD databases were designed to provide a standard benchmark for evaluating the performances of different connected digit recognition systems. It is also a vehicle for research and diagnosis of specific problems in automatic connected digit recognition. We first describe the content and the organization of the BLCD databases, and then present an automatic database verification procedure utilizing automatic speech recognition (ASR). For reference, we present automatic speech recognition performance on a set of the databases using the Bell Labs ASR system. For the databases with good recording conditions, the word-error rates can be less than 1%. In order to promote speech science and technology for real world applications, we make this database available for the speech community.