WhisperX-LLM-TermFixer: Enhancing Whisper with LLM-Guided Post-Decoding for Domain-Specific Terminology

Ronghao Pan, José Antonio García-Díaz, Rafael Valencia-García


Abstract
Large-scale ASR models such as Whisper perform well in general domains but struggle with specialized terminology, particularly in sensitive domains like medicine. We propose WhisperX-LLM-TermFixer, a lightweight post-decoding framework that improves term recognition without retraining or modifying the acoustic model. The method combines N-best decoding, phonetic n-gram correction, and LLM-based contextual filtering. We evaluate the method on a controlled synthetic benchmark containing 1,005 utterances per language in English, Spanish, Catalan, and Basque, with one target medical term per utterance and full lexicon coverage. Across six Whisper sizes, the selected configurations improve term accuracy by 16.12-35.32 percentage points and reduce WER by 0.88-4.01 points relative to WhisperX. LLM filtering reduces WER relative to the phonetic stage in all evaluated configurations, although it reduces term accuracy in three Basque configurations. Perplexity results provide additional evidence of improved linguistic plausibility. The selected configurations require approximately 1.26x-2.38x the baseline inference time. Our code and data are publicly available at https://github.com/NLP-UMUTeam/WhisperX-LLM-TermFixer.
Anthology ID:
2026.findings-aacl.153
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
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Pages:
3019–3042
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URL:
https://aclanthology.org/2026.findings-aacl.153/
DOI:
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Cite (ACL):
Ronghao Pan, José Antonio García-Díaz, and Rafael Valencia-García. 2026. WhisperX-LLM-TermFixer: Enhancing Whisper with LLM-Guided Post-Decoding for Domain-Specific Terminology. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 3019–3042, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
WhisperX-LLM-TermFixer: Enhancing Whisper with LLM-Guided Post-Decoding for Domain-Specific Terminology (Pan et al., Findings 2026)
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https://aclanthology.org/2026.findings-aacl.153.pdf