Subspace Gaussian mixture model for computer-assisted language learning

In computer-assisted language learning (CALL), speech data from non-native speakers are usually insufficient for acoustic modeling. Subspace Gaussian Mixture Models (SGMM) have been effective in training automatic speech recognition (ASR) systems with limited amounts of training data. Therefore, in this work, we propose to use SGMM to improve the fluency assessment performance. In particular, the contributions of this work are: (i) The proposed SGMM acoustic model trained with native data outperforms the MMI-GMM/HMM baseline by 25% relative, (ii) when incorporating a small amount of non-native training data, the SGMM acoustic model further improves the performance of fluency assessment by 47% relative.