Title: TTS Can Speak in Any Style with Any Voice
Primary area: applications to computer vision, audio, language, and other modalities
Keywords: Instruction TTS, Controllable Speech Synthesis, Decoupling, Reinforcement Learning

Abstract: This study proposes FlexiVoice, a text-to-speech (TTS) synthesis system speaking in any style with any voice. The speaking style is controlled by a natural-language instruction and the voice timbre is provided by a speech reference in zero-shot manner. FlexiVoice is built with an LLM core, which takes text as input, and also takes an optional natural language instruction and an optional speech reference to control style and timbre, respectively. FlexiVoice is equipped with a novel Progressive Post-Training (PPT) scheme that progressively unlocks accurate and flexible controllability. In particular, it first employs Direct Preference Optimization (DPO) to enable FlexiVoice to accurately follow both natural language instruction and speech reference simultaneously. It then uses a multi-objective Group Relative Policy Optimization (GRPO) to disentangle style instruction, reference timbre, and textual content. Finally, it adapts instruction GRPO for more advanced instruction following. Experimental results show that FlexiVoice surpasses competing baselines and demonstrates strong capability in decoupling control factors. Human evaluations further confirm its naturalness, controllability, and robustness.
Audio samples are available at https://flexi-voice.github.io/.