---
language:
- mn
license: apache-2.0
base_model: openai/whisper-small
tags:
- whisper
- automatic-speech-recognition
- mongolian
- cyrillic
- speech
datasets:
- Blgn94/mongolian-stt-dataset-v24
metrics:
- wer
- cer
library_name: transformers
pipeline_tag: automatic-speech-recognition
model-index:
- name: whisper-small-mn-v25
  results:
  - task:
      type: automatic-speech-recognition
      name: Automatic Speech Recognition
    dataset:
      name: mongolian-stt-dataset-v24 (text-disjoint clean split)
      type: Blgn94/mongolian-stt-dataset-v24
      split: validation (clean)
    metrics:
    - type: wer
      value: 21.33
      name: WER
    - type: wer
      value: 19.67
      name: WER (normalized)
    - type: cer
      value: 9.13
      name: CER (normalized)
---

# whisper-small-mn-v25

Fine-tune of [`openai/whisper-small`](https://huggingface.co/openai/whisper-small) for
**Mongolian (Cyrillic Khalkha) speech-to-text**. This is the **v25** run — the winning
configuration of a controlled A/B against a plain fine-tuning baseline, selected on a
**text-disjoint** evaluation set (transcripts that never appear in training) rather than the
optimistic in-domain split.

- **Base model:** `openai/whisper-small` (244M params)
- **Language:** Mongolian, Cyrillic script (mn)
- **Dataset:** [`Blgn94/mongolian-stt-dataset-v24`](https://huggingface.co/datasets/Blgn94/mongolian-stt-dataset-v24) (~148 h of audio)
- **Honest clean WER:** **21.33** (raw) / **19.67** (normalized)

## Results

All numbers are Word/Character Error Rate (lower is better). Normalized = lowercased,
punctuation stripped, NFC-normalized Cyrillic (ё/й) — this is what published benchmarks use,
so compare against the `_norm` columns.

Three evaluation sets are reported:

| eval set | what it is | trust |
|---|---|---|
| **clean** | dev clips whose transcripts **never** appear in training (241 clips) | the honest metric — **model was selected on this** |
| **indomain** | old random split; ~89% of its transcripts also appear in training (300 clips) | optimistic (memorization), kept for continuity |
| **mic** | 10 clips recorded on a laptop mic — real, noisy, out-of-distribution | reported only, too small to trust |

### v25 final metrics

| eval set | WER | CER | WER (norm) | CER (norm) |
|---|---|---|---|---|
| **clean** | 21.33 | 9.78 | **19.67** | 9.13 |
| indomain | 23.01 | 8.40 | 21.04 | 7.92 |
| mic | 84.36 | 48.66 | 72.51 | 44.87 |

Per-source normalized WER on the clean set: **mbspeech 6.03**, **fleurs 21.67**,
**youtube 57.65** (spontaneous speech is the weak spot — see Limitations).

### A/B vs baseline (the reason this recipe was chosen)

Both runs share the identical text-disjoint `clean` eval set, so the comparison is fair.

| metric (normalized) | baseline | **v25** | Δ |
|---|---|---|---|
| **clean WER** (selection metric) | 22.85 | **19.67** | **−3.18** |
| clean CER | 9.82 | 9.13 | −0.69 |
| clean — mbspeech | 8.18 | 6.03 | −2.14 |
| clean — youtube (spontaneous) | 66.15 | 57.65 | **−8.50** |
| mic (real-world) | 87.68 | 72.51 | **−15.17** |
| indomain (optimistic) | 17.07 | 21.04 | +3.97 |

The baseline is a plain fine-tune on the full corpus with no de-duplication or augmentation.
v25 improves the **honest** clean WER by 3.2 points and generalizes markedly better on
spontaneous YouTube speech and on real microphone recordings. The in-domain score *rises* —
this is expected and desirable: capping duplicate transcripts removes the memorization crutch
(the corpus repeats each Common Voice sentence ~14.5×), so the optimistic in-domain number
falls while genuine transcription of unseen speech improves.

## Training data

[`Blgn94/mongolian-stt-dataset-v24`](https://huggingface.co/datasets/Blgn94/mongolian-stt-dataset-v24)
— ~148 h of 16 kHz Mongolian Cyrillic speech across four sources (measured by decoding all clips):

| source | ~hours | notes |
|---|---|---|
| Common Voice | ~126 | read speech; only ~6,000 distinct sentences (~14.5× text reuse) |
| FLEURS | ~14 | read speech |
| MBSpeech | ~7 | read speech |
| YouTube | ~1 | manual-subtitle clips — the only spontaneous speech |

**Known weakness:** the corpus is ~85% Common Voice read speech and very light on spontaneous
speech (~1 h). Read-speech sources score in the single-to-low-twenties WER; spontaneous
YouTube sits near 58%. Expect the model to be strongest on clear, read-style Mongolian and
weaker on conversational/noisy audio.

### v25 corpus shaping (what makes this run different)

- **Per-sentence cap = 4:** at most 4 recordings per distinct transcript, dropping 66.5% of
  rows (95,946 → 32,134) and cutting Common Voice text reuse from 14.5× to 4×. Breaks the
  transcript-memorization shortcut.
- **Source-balanced sampling (α = 0.5):** re-weights so Common Voice does not drown out FLEURS,
  MBSpeech, and YouTube.
- **Audio augmentation (train only; eval always clean):**
  - SpecAugment (time masking, p = 0.05)
  - Waveform augmentation (p = 0.5, up to 2 ops): speed 0.9–1.1×, gain, additive noise at
    10–30 dB SNR, light reverb.

## Training procedure

| | |
|---|---|
| Base model | `openai/whisper-small` |
| Precision | bf16 |
| Effective batch | 16 (batch 4 × grad-accum 4) |
| Learning rate | 1e-5, linear schedule, warmup ratio 0.05 |
| Weight decay | 0.01 |
| Label smoothing | 0.0 |
| Epochs | 4 (8,036 steps) |
| Max label tokens | 440 |
| Seed | 42 |
| Hardware | 1× NVIDIA RTX 5060 (8 GB, Blackwell) |
| Wall-clock | ~2 h 53 m |
| transformers / torch | 5.14.1 / 2.13.0+cu130 |

Model selection: best checkpoint by `eval_clean_wer_norm` (`load_best_model_at_end`).
Labels drop the leading `<|startoftranscript|>` token (the model re-prepends
`decoder_start_token_id`).

### Reproduce

```bash
MAX_PER_SENTENCE=4 SOURCE_ALPHA=0.5 AUG_PROB=0.5 EPOCHS=4 OUT=out_v25 \
  python scripts/train.py
```

Full config and final metrics are in `run_manifest.json` in this repo.

## Usage

```python
import torch
from transformers import pipeline

pipe = pipeline(
    "automatic-speech-recognition",
    model="Blgn94/whisper-small-mn-v25",
    device=0 if torch.cuda.is_available() else -1,
)
result = pipe(
    "audio.mp3",
    generate_kwargs={"language": "mn", "task": "transcribe"},
)
print(result["text"])
```

For long audio, add `chunk_length_s=30`. For raw model + processor access:

```python
from transformers import WhisperForConditionalGeneration, WhisperProcessor

processor = WhisperProcessor.from_pretrained("Blgn94/whisper-small-mn-v25")
model = WhisperForConditionalGeneration.from_pretrained("Blgn94/whisper-small-mn-v25")
```

## Limitations

- **Spontaneous / conversational speech:** weak (~58% WER on YouTube), because the corpus has
  only ~1 h of it. Real-world microphone input is also harder (mic set ~72% WER, but only
  10 clips — treat as directional, not a benchmark).
- **Not evaluated on the official Common Voice test split.** The `clean` set is a custom
  text-disjoint split of v24; it is *not* speaker-disjoint from training, so real-world WER on
  entirely new speakers may be somewhat higher. For a speaker-disjoint reference point,
  `bayartsogt/whisper-small-mn-8` reports ~26.5% WER on the official Common Voice mn test.
- **Cyrillic Khalkha only.** No traditional Mongolian script; not tuned for other dialects.

## License

Apache-2.0, inheriting from the `openai/whisper-small` base model. Note the underlying
training data combines sources under their own licenses (Common Voice, FLEURS, MBSpeech,
YouTube manual subtitles); review those before commercial use.