Phoneme- and Word-Level Metrics Using Self-Supervised Speech Representations for Forced Alignment Evaluation

V.S.D.S.Mahesh Akavarapu, Michael Daniel, Gerhard Jäger


Abstract
Forced alignment evaluation typically requires manually annotated timestamps, limiting large-scale and multilingual analysis. We introduce two corpus-level metrics based on self-supervised (SSL) speech representations for reference-free forced alignment evaluation: Phoneme-Cluster Mutual Information (PCMI) and Word Acoustic Consistency Score (WACS). PCMI measures agreement between aligned phoneme labels and clusters induced from SSL-speech representations, while WACS measures consistency of repeated word realizations using dynamic time warping similarity between word representation sequences. Using both random and systematic perturbations, we show that PCMI and WACS degrade consistently under alignment perturbations. We further analyze the metrics across multiple alignment systems on 85 languages from FLEURS, validate them against manually annotated alignments from 45 languages in DoReCo, and evaluate them on two phonologically complex low-resource languages. The metrics effectively separate high- and low-quality alignments and correlate strongly with timestamp-based alignment quality measures. Our results demonstrate that SSL-speech representations enable scalable, reference-free forced alignment evaluation. The metrics are available as an open-source Python package at https://github.com/mahesh-ak/forced-aligner-metrics.
Anthology ID:
2026.findings-emnlp.279
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
5865–5892
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URL:
https://aclanthology.org/2026.findings-emnlp.279/
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Cite (ACL):
V.S.D.S.Mahesh Akavarapu, Michael Daniel, and Gerhard Jäger. 2026. Phoneme- and Word-Level Metrics Using Self-Supervised Speech Representations for Forced Alignment Evaluation. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 5865–5892, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Phoneme- and Word-Level Metrics Using Self-Supervised Speech Representations for Forced Alignment Evaluation (Akavarapu et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.279.pdf