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Kinetic-Optimal Scheduling with Moment Correction for Metric-Induced Discrete Flow Matching in Zero-Shot Text-to-Speech
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Proposes GibbsTTS: a training-free constant-Fisher-Rao-speed scheduler and a finite-step moment correction for metric-induced discrete flow matching, applied to codec-token zero-shot TTS.
Problem
Metric-induced discrete flow matching (MI-DFM) relies on heuristic time schedulers needing hyperparameter search and suffers finite-step path-tracking error from a first-order CTMC solver, limiting its use in zero-shot TTS.
Approach
Derives a kinetic-optimal (constant Fisher-Rao speed) scheduler for prescribed scalar-parameterized paths and computes it numerically from token-embedding distance matrices, plus a finite-step moment correction that adjusts only the jump probability while keeping the jump destination distribution fixed.
Key results
- GibbsTTS (Numerical KO + corrector) reaches UTMOS 3.651, WER 1.777% and SIM 0.743 on Seed-TTS test-en, best among masked generative baselines.
- Removing the moment corrector lowers UTMOS on Seed-TTS test-en from 3.651 to 3.403 and raises WER from 1.777% to 2.120%.
- GibbsTTS attains the highest speaker similarity on three of four SOTA comparison test sets (e.g., 0.790 on Seed-TTS test-zh), second on CosyVoice 3 en behind OmniVoice.
Surprising findings
- The MaskGCT sin scheduler performs poorly with masked DFM but is strongest among masked DD schedulers, showing scheduler choice is coupled to decoding formulation.
- GibbsTTS is not the strongest system on naturalness or WER/CER against larger AR and recent NAR systems, so SOTA gains are mainly in speaker similarity.
Limitations
- Distance is restricted to cosine-equivalent codebook distance; other token metrics and geometry not explored.
- Corrector uses an unconditional reference moment, so it is an approximation and does not recover the infinitesimal CTMC limit as h→0.
- Only evaluated on zero-shot TTS; SOTA comparisons are not fully controlled and GibbsTTS trails on naturalness and WER/CER.
Experimental setup
Datasets: Emilia-en Emilia-zh LibriTTS test-clean Seed-TTS test-en Seed-TTS test-zh CosyVoice 3 test sets
Benchmarks: Seed-TTS test-en Seed-TTS test-zh CosyVoice 3 en CosyVoice 3 zh
Metrics: UTMOS WER CER SIM CMOS SMOS
Baselines: MI-DFM grid-searched scheduler Masked DFM closed-form KO DiFlow-TTS MaskGCT F5-TTS OmniVoice Spark-TTS FireRedTTS-2 IndexTTS2 CosyVoice 2 CosyVoice 3 Qwen3-TTS
Builds on: metric-induced discrete flow matching discrete flow matching MaskGCT kinetic-optimal discrete probability paths DiT
Closest papers by meaning
- Trajectory as the Teacher: Few-Step Discrete Flow Matching via Energy-Navigated Distillation (NeurIPS 2026 · similarity 0.87)
- DMOSpeech: Direct Metric Optimization via Distilled Diffusion Model in Zero-Shot Speech Synthesis (ICML 2025 · similarity 0.85)
- Shallow Flow Matching for Coarse-to-Fine Text-to-Speech Synthesis (NeurIPS 2025 · similarity 0.85)
- Discrete Flow Matching (NeurIPS 2024 · similarity 0.85)
- MaskGCT: Zero-Shot Text-to-Speech with Masked Generative Codec Transformer (ICLR 2025 · similarity 0.84)
- CLaM-TTS: Improving Neural Codec Language Model for Zero-Shot Text-to-Speech (ICLR 2024 · similarity 0.84)
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