Open Automatic Speech Recognition Models for Classical and Modern Standard Arabic
Summary
Arabic speech recognition still has few strong open models. Most existing work covers Modern Standard Arabic (MSA) and largely ignores Classical Arabic (CA), the fully vowelized language of the Quran. Short vowels are usually left out of written Arabic, so systems that drop diacritics produce ambiguous text. The NVIDIA authors built an open preprocessing pipeline for Arabic audio and text in NeMo-speech-data-processor. It fixes the character inventory, normalizes Unicode and numerals, and filters noisy or mislabeled clips. With it they trained two FastConformer models using hybrid RNN-T/CTC decoding on openly licensed corpora: MASC, MCV17.0, FLEURS and EveryAyah. The first model handles MSA and outputs punctuation. The second is described as the first public model covering both MSA and CA, and it also predicts diacritics. The authors report state-of-the-art results for MSA, including blind tests on MGB2 and MediaSpeech, and the best diacritized CA accuracy. Checkpoints and recipes are released under a commercial-friendly license, which gives others a reproducible baseline for Arabic and for diacritized ASR.
Key points
- The two checkpoints on HuggingFace are
stt_ar_fastconformer_hybrid_large_pc_v1.0(MSA, with punctuation) and..._pcd_v1.0(MSA+CA, with punctuation and diacritics). - The output alphabet has 36 Arabic characters: 28 base letters, six Hamza forms, Ta' Marbuta and Alif Maksura. Adding Fathah, Kasrah, Dammah, Sukun, Tanween and Shaddah brings it to 44 symbols. Only three punctuation marks are kept.
- The training corpora are MASC (646h clean + 855h noisy raw), MCV17.0 Arabic, FLEURS Arabic and EveryAyah, with EveryAyah used only for the CA model. MGB2 and MediaSpeech are used solely as blind test sets.
- Filtering with a pretrained model's WER/CER and with word-rate and character-rate checks recovered roughly 120h of extra usable clean MASC audio and 40h of noisy audio.
- The EveryAyah test set had train/test text overlap. Removing it shrank the test set from 100h to 23h, and results are given on both versions. Training used dropout 0.1, SpecAugment with 4 frequency masks and 20 time masks, and a CTC weight of 0.3.
Interesting ideas
- I1. Leakage between train and test is checked only after stripping diacritics and punctuation, because the same sentence can reappear with different markup or a different speaker. — For Mova (learn): Before scoring, deduplicate treebank and silver splits on a normalized form (lowercased, punctuation and casing removed), so a reworded copy of a training sentence cannot inflate LAS.
- I2. An already trained model screens new training data, and clips it transcribes very badly are treated as likely label noise rather than hard examples. — For Mova (learn): Let the witness parsers score incoming silver sentences and drop those where every witness scores very poorly against the proposed tree, keeping noisy text out of training.
- I3. The symbol inventory is closed and explicit: any sample containing an out-of-alphabet character is discarded, and NFKC is applied first so positional letter forms and stacked marks become one canonical sequence. — For Mova (tokens): Declare a fixed character set for the en tokenizer and canonicalize Unicode (ligatures, quote variants, combining marks) before tagging, so that rare glyphs do not create spurious lemmas.
- I4. Each benchmark is scored only after the model output is converted to that benchmark's own normalization (letter folding for MASC and MediaSpeech), and the models are never trained on the evaluation corpus. — For Mova (tree): Evaluate gparse blind on treebanks it never trained on, after converting its output into the target UD dialect, so that the score reflects parsing quality and not annotation-convention mismatch.
- I5. The release keeps two variants of the same model, one with plain output and one that also predicts diacritics, so users can pick the richer layer when they need it without losing the simpler one. — For Mova (back): Generation could likewise offer a plain surface form and an annotated variant with explicit morphology or role marks, checking that both come from the same meaning graph.
Cited by
Cite
@misc{grigoryan2025open,
title = {{Open Automatic Speech Recognition Models for Classical and Modern Standard Arabic}},
author = {Grigoryan, Lilit and Karpov, Nikolay and Albasiri, Enas and Lavrukhin, Vitaly and Ginsburg, Boris},
year = {2025},
doi = {10.48550/arxiv.2507.13977},
eprint = {2507.13977},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2507.13977}
}References
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