MFA Acoustic Model for Quranic Recitation (Hafs)

A Montreal Forced Aligner acoustic model purpose-built for Quranic recitation in the Hafs riwaya, with a pronunciation dictionary derived from a rule-verified phonetic script. Built for phone-level tajweed measurement: madd durations, ghunna, qalqala, not just word timestamps.

What makes it different

Generic Arabic aligners fail on recitation: multi-second madd vowels, ghunna nasals, melismatic (mujawwad) style, and mosque reverb are far outside normal speech. This model was trained and evaluated specifically against those:

• Phone set: derived from the Quran Phonetic Script via quran-transcript, re-encoded so every articulation is ONE phone (ا+ = long vowel of any prescribed length, vs. the source convention of repeating characters, which is degenerate for HMM alignment). 67 symbols; tajweed-bearing segments are single intervals.
• Pronunciation dictionary: whole-ayah contextual phonetization (wasl forms, cross-word idgham/ikhfa/iqlab), never isolated-word forms, which measure 20.5% phone error vs. 1.6% for contextual.
• Training data (~110 h, style-balanced): human-word-count-validated ayah clips from QUL reciters, a targeted lazem/mottasel oversample, and 40 h of mujawwad cut from a large verified crawl. Balance matters: a 5x larger unbalanced corpus degraded mujawwad coverage in our ablations.
• Training config: silence_probability 0.15, boost_silence 1.0 (defaults subsidize the silence model, which then swallows sustained vowels), beams 40/160 for multi-second phones.

Measured performance

Notes for measurement use: word-onset comparisons against QUL word timings are biased: QUL starts are ~245 ms early vs. physical burst landmarks (playback convention). Trust obstruent-anchored spans; treat boundaries inside sonorant runs as untrustworthy and measure rule segments between obstruent anchors. Pre-pause madds benefit from an energy/voicing end-trim (breath and room decay otherwise attach to the final phone).

Files

Usage

mfa align CORPUS_DIR quran_hafs.dict quran_hafs_acoustic.zip OUT_DIR \
  --beam 40 --retry_beam 160

Corpus: one wav (16 kHz mono) + one .lab per ayah clip, .lab containing the Uthmani ayah text (whole words; the dictionary handles phonetization). Keep all paths ASCII (OpenFST on Windows fails on non-ASCII paths).

Limitations

• Hafs only. The phonetizer supports no other riwaya; aligning Warsh/Qalun audio with this model would systematically mislabel exactly the features tajweed cares about.
• Mid-ayah waqf is unmodelled (the Uthmani text carries no waqf marks); a reciter pausing mid-ayah takes pausal forms the dictionary does not offer.
• Mujawwad residual: ~5% of sung speech (mostly pre-breath decrescendos) is attributed to silence; use signal-side end-trims for duration work there.
• One model, deliberately: a mujawwad-specialist ablation underperformed this balanced model, and MFA performs per-speaker adaptation at align time.

Provenance

Built by the Quran-Lab effort on a 59,000-hour multi-site crawl of public recitation audio (verified per-ayah against canonical text before any training; label source is always the canonical Uthmani text, never ASR output). Phone representation and rule index from the companion quran-phones package.