Improving Speech Recognition using GAN-based Speech Synthesis and Contrastive Unspoken Text Selection

Text-to-Speech synthesis (TTS) based data augmentation is a relatively new mechanism for utilizing text-only data to improve automatic speech recognition (ASR) training without parameter or inference architecture changes. However, efforts to train speech recognition systems on synthesized utterances suffer from limited acoustic diversity of TTS outputs. Additionally, the text-only corpus is always much larger than the transcribed speech corpus by several orders of magnitude, which makes speech synthesis of all the text data impractical. In this work, we propose to combine generative adversarial network (GAN) and multi-style training (MTR) to increase acoustic diversity in the synthesized data. We also present a contrastive language model-based data selection technique to improve the efficiency of learning from unspoken text. We demonstrate that our proposed method allows ASR models to learn from synthesis of large-scale unspoken text sources and achieves a 35% relative WER reduction on a voice-search task.