# LCS-CTC: Leveraging Soft Alignments to Enhance Phonetic Transcription Robustness

arXiv: https://arxiv.org/abs/2508.03937 · HTML: https://mlsanity.com/paper/2508.03937/

## Key facts

- Cited by 3 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 5 Aug 2025.

## Built on by (most cited first, 3 of 3)

- [Revisiting Rule-Based Stuttering Detection: A Comprehensive Analysis of Interpretable Models for Clinical Applications](https://mlsanity.com/paper/2508.16681/) (2025)
- [A Comparative Study of Controllability, Explainability, and Performance in Dysfluency Detection Models](https://mlsanity.com/paper/2509.00058/) (2025)
- [Deploying UDM Series in Real-Life Stuttered Speech Applications: A Clinical Evaluation Framework](https://mlsanity.com/paper/2509.14304/) (2025)

## Abstract (arXiv)

Phonetic speech transcription is crucial for fine-grained linguistic analysis and downstream speech applications. While Connectionist Temporal Classification (CTC) is a widely used approach for such tasks due to its efficiency, it often falls short in recognition performance, especially under unclear and nonfluent speech. In this work, we propose LCS-CTC, a two-stage framework for phoneme-level speech recognition that combines a similarity-aware local alignment algorithm with a constrained CTC training objective. By predicting fine-grained frame-phoneme cost matrices and applying a modified Longest Common Subsequence (LCS) algorithm, our method identifies high-confidence alignment zones which are used to constrain the CTC decoding path space, thereby reducing overfitting and improving generalization ability, which enables both robust recognition and text-free forced alignment. Experiments on both LibriSpeech and PPA demonstrate that LCS-CTC consistently outperforms vanilla CTC baselines, suggesting its potential to unify phoneme modeling across fluent and non-fluent speech.