Decoding Strategies for Diffusion-Based ASR: A Systematic Evaluation of Confidence-Based Thresholding

Jeong Hun Yeo, Minsu Kim, Hyeongseop Rha, Yong Man Ro


Abstract
While LLM-based Automatic Speech Recognition (ASR) achieves high accuracy, its speed is limited by sequential autoregressive decoding. Diffusion Language Models (DLMs) offer a parallel alternative, yet their decoding strategies remain under-explored in ASR contexts. This paper analyzes three decoding schemes for DLM-based ASR: fixed-number, static confidence threshold, and dynamic confidence threshold. We introduce a round-wise analysis of decoding progress using Negative Log-Likelihood-based uncertainty as a proxy for prediction reliability. Our results show that both threshold-based strategies provide a better accuracy–speed trade-off than fixed-number schemes. This behavior is associated with the more concentrated confidence distribution observed in the evaluated ASR settings: many tokens reach high confidence early, enabling multiple tokens to be committed in early decoding rounds while lower-confidence tokens are deferred to later rounds. The static-threshold strategy achieves accuracy close to autoregressive decoding at lower decoding cost.
Anthology ID:
2026.emnlp-main.1829
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Junyi Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
41652–41663
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1829/
DOI:
10.18653/2026.emnlp-main.1829
Bibkey:
Cite (ACL):
Jeong Hun Yeo, Minsu Kim, Hyeongseop Rha, and Yong Man Ro. 2026. Decoding Strategies for Diffusion-Based ASR: A Systematic Evaluation of Confidence-Based Thresholding. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 41652–41663, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Decoding Strategies for Diffusion-Based ASR: A Systematic Evaluation of Confidence-Based Thresholding (Yeo et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1829.pdf