Enhancing the Stability of LLM-based Speech Generation Systems through
  Self-Supervised Representations
Álvaro Martín-Cortinas Daniel Sáez-Trigueros Iván Vallés-Pérez Biel Tura-Vecino Piotr Biliński Mateusz Lajszczak Grzegorz Beringer Roberto Barra-Chicote Jaime Lorenzo-Trueba
Large Language Models (LLMs) are one of the most promising technologies for
the next era of speech generation systems, due to their scalability and
in-context learning capabilities. Nevertheless, they suffer from multiple
stability issues at inference time, such as hallucinations, content skipping or
speech repetitions. In this work, we introduce a new self-supervised Voice
Conversion (VC) architecture which can be used to learn to encode transitory
features, such as content, separately from stationary ones, such as speaker ID
or recording conditions, creating speaker-disentangled representations. Using
speaker-disentangled codes to train LLMs for text-to-speech (TTS) allows the
LLM to generate the content and the style of the speech only from the text,
similarly to humans, while the speaker identity is provided by the decoder of
the VC model. Results show that LLMs trained over speaker-disentangled
self-supervised representations provide an improvement of 4.7pp in speaker
similarity over SOTA entangled representations, and a word error rate (WER)
5.4pp lower. Furthermore, they achieve higher naturalness than human recordings
of the LibriTTS test-other dataset. Finally, we show that using explicit
reference embedding negatively impacts intelligibility (stability), with WER
increasing by 14pp compared to the model that only uses text to infer the
style.