Automatic speech recognition performance on a voicemail transcription task

We report on the performance of automatic speech recognition (ASR) systems on voicemail transcription. Voicemail is spontaneous telephone speech recorded over a variety of channels; consequently, it is representative of many challenging problems in speech recognition. In the course of working on this task, several algorithms were developed that focus on different components of an ASR system, including lexicon design, feature extraction, hypothesis search, and adaptation. We report the improvements provided by these techniques, as well as other standard techniques, on a voicemail test set. Although the techniques are benchmarked on voicemail test data, their scope is not restricted to this domain as they address fundamental aspects of the speech recognition process.