Efficient Acoustic Modeling Method for Unsupervised Speech Recognition using Multi-Task Deep Neural Network

This paper proposes a method of acoustic modeling for zero-resourced languages speech recognition under mismatch conditions. In those languages, very limited or no transcribed speech is available for traditional monolingual speech recognition. Conventional methods such as IPA based universal acoustic modeling has been proved to be effective under matched acoustic conditions (similar speaking styles, adjacent languages, etc.), while usually poorly preformed when mismatch occurs. Since mismatch problems between languages often appears, in this paper, unsupervised acoustic modeling via cross-lingual knowledge sharing has thus been proposed: first, initial acoustic models (AM) for a target zero-resourced language are trained using Multi-Task Deep Neural Networks (MDNN)-different languages' speech mapped to the phonemes of the target language (mapped data) is jointly trained together with the same data transcribed language specifically and respectively (specific data); then, automatically transcribed target language data is used in the iterative process to train new AMs, with various auxiliary tasks. Experiment on 100 hour Japanese speech without transcripts achieved a character error rate (CER) of 57.21%, 19.32% absolute improvement compared to baseline (IPA based universal acoustic modeling).