Dysarthric Speech Augmentation Using Prosodic Transformation and Masking for Subword End-to-end ASR

End-to-end speech recognition systems are effective, but in order to train an end-to-end model, a large amount of training data is needed. For applications such as dysarthric speech recognition, we do not have sufficient data. In this paper, we propose a specialized data augmentation approach to enhance the performance of an end-to-end dysarthric ASR based on sub-word models. The proposed approach contains two methods, including prosodic transformation and time-feature masking. Prosodic transformation modifies the speaking rate and pitch of normal speech to control prosodic characteristics such as loudness, intonation, and rhythm. Using time and feature masking, we apply a mask to the Mel Frequency Cepstral Coefficients (MFCC) for robustness-focused augmentation. Results show that augmenting normal speech with prosodic transformation plus masking decreases CER by 5.4% and WER by 5.6%, and the further addition of dysarthric speech masking decreases CER by 11.3% and WER by 11.4%.