Integrating acoustic and state-transition models for free phone recognition in L2 English speech using multi-distribution deep neural networks

This paper investigates the use of Multi-Distribution Deep Neural Networks (MD-DNNs) for integrating acoustic and statetransition models in free phone recognition of L2 English speech. In Computer-Aided Pronunciation Training (CAPT) system, free phone recognition for L2 English speech is the key model of Mispronunciation Detection and Diagnosis (MDD) in the cases of allowing freely speaking. A simple Automatic Speech Recognition (ASR) system can be approached with an Acoustic Model (AM) and a State-Transition Model (STM). Generally, these two models are trained independently, hence contextual information maybe lost. Inspired by the AcousticPhonological Model, which achieves greatly improvements by integrating the AM and Phonological Model (PM) in MDD for the cases that L2 learners practice their English by following the prompts, we propose a joint Acoustic-State-Transition Model (ASTM) which uses a MD-DNN to integrate the AM and STM. Preliminary experiments with basic parameter configurations show that the ASTM obtains a phone accuracy of about 68% on the TIMIT data. It is better than the system of using separate AM and STM, whose accuracy is only about 52%. Further finetuning the ASTM achieves an accuracy of about 72% on the TIMIT data. Similar performance is obtained if we train and test the ASTM on our L2 English speech corpus (CU-CHLOE).