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Replacing a frozen TTS model with one mean log-mel vector per phoneme made text injection for speech recognition 1.8 times faster at comparable word error rate

AspireAI community · arXiv (One Mean Log-Mel Vector per Phoneme, Zeyer et al., RWTH Aachen)
Text injection trains speech recognition on unpaired text alongside paired audio, and the usual way to synthesize the speech encoder's input is to run a frozen text-to-speech model. This work replaces that TTS model with a lookup table: a mean log-mel vector, or one-hot encoding, per phoneme, repeated for a random duration drawn from alignment statistics, with silence between words. Training is 1.8 times faster than with the neural TTS at comparable word error rates, and with an external language model the system reaches 1.36 / 2.90 / 1.52 / 3.24 percent WER on LibriSpeech dev and test, clean and other, which the authors report as state of the art using only LibriSpeech paired data, text and lexicon. The code for every number is public. The honest limit: the synthetic input is phoneme-level, so it carries no speaker or acoustic detail.
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