Title: UniTTS: Towards End-to-End Speech Synthesis with Joint Acoustic-Semantic Modeling
Primary area: foundation or frontier models, including LLMs
Keywords: Neutral Audio Codec, Speech Synthesis, TTS, Audio Lanuage Model

Abstract: Recent advancements in multi-codebook neutral audio codecs, such as Residual Vector Quantization (RVQ) and Group Vector Quantization (GVQ), have significantly advanced text-to-speech (TTS) systems based on large language models (LLMs), whose exceptional capabilities in discrete token modeling have garnered significant attention within the speech processing community. However, since semantic and acoustic information cannot be fully aligned, a significant drawback of these methods when applied to LLM-based TTS is that large language models may have limited access to comprehensive audio information. To address this limitation, we propose DistilCodec and UniTTS, which collectively offer the following advantages: 1) DistilCodec distills a multi-codebook audio codec into a single-codebook codec with 32,768 codes, achieving near 100\% codebook utilization. 2) By avoiding semantic alignment constraints, DistilCodec enables the incorporation of extensive high-quality unlabeled audio—such as audiobooks with sound effects and musical segments—during training, thereby enhancing data diversity and general applicability. 3) Leveraging the comprehensive audio information modeling of DistilCodec, we integrated three key tasks into UniTTS's pre-training framework: audio modality autoregression, text modality autoregression, and speech-text cross-modal autoregression. This allows UniTTS to accept interleaved text and speech/audio prompts while substantially preserving LLM's text capabilities. 4) UniTTS employs a three-stage training process: Pre-Training, Supervised Fine-Tuning (SFT), and Alignment. Experiments demonstrate that DistilCodec effectively resolves codebook collapse in large, single-codebook settings. Building on this, UnitTTS demonstrates remarkable capabilities for zero-shot voice cloning with emotional expression.

TL;DR: We introduce DistilCodec, a high-utilization single audio codec, and UniTTS, an end-to-end TTS system leveraging the DistilCodec representation for generation without acoustic-semantic decoupling.