| --- |
| license: apache-2.0 |
| language: |
| - de |
| tags: |
| - truecasing |
| - text-processing |
| - german |
| - nlp |
| - lstm |
| - crf |
| pipeline_tag: token-classification |
| --- |
| |
| # Truecaser Models |
|
|
| Truecasing models for restoring proper capitalization in lowercase ASR output. Used by [CrispASR](https://github.com/CrispStrobe/CrispASR) via `--truecase-model`. |
|
|
| ## Available Models |
|
|
| | File | Type | Language | Size | F1 | License | Flag | |
| |------|------|----------|------|-----|---------|------| |
| | `truecaser-lstm-de.bin` | BiLSTM char-level | German | 3.2 MB | 97.9% | Apache-2.0 | `lstm` or `lstm-de` | |
| | `truecaser-lstm-en.bin` | BiLSTM char-level | English | 3.2 MB | 93.0% | Apache-2.0 | `lstm-en` | |
| | `truecaser-lstm-es.bin` | BiLSTM char-level | Spanish | 3.2 MB | — | Apache-2.0 | `lstm-es` | |
| | `truecaser-lstm-ru.bin` | BiLSTM char-level | Russian | 4.1 MB | — | Apache-2.0 | `lstm-ru` | |
| | `truecaser-crf-de.bin` | CRF + context | German | 8.5 MB | ~95% | MIT | `crf` | |
| | `truecaser-de.bin` | Statistical freq | German | 1.7 MB | ~93% | MIT | `auto` | |
|
|
| ## BiLSTM Truecaser (recommended) |
|
|
| Converted from [mayhewsw/pytorch-truecaser](https://github.com/mayhewsw/pytorch-truecaser) (Apache-2.0). |
|
|
| - **Architecture**: Embedding(202, 50) → BiLSTM(50→150, 2 layers) → Linear(300, 2) |
| - **Labels**: L (lowercase), U (uppercase) — per character |
| - **Training**: WMT monolingual text (de: 2.6M tokens, 97.86% F1; en: Wikipedia, 93.01% F1; es: WMT; ru: LORELEI) |
| - **Original paper**: Mayhew et al., "NER and POS When Nothing is Capitalized" (2019) |
| - **Source**: [mayhewsw/pytorch-truecaser v1.0](https://github.com/mayhewsw/pytorch-truecaser/releases/tag/v1.0) — `wmt-truecaser-model-de.tar.gz` |
|
|
| ### Example |
|
|
| ``` |
| Input: die schnelle braune katze springt über den faulen hund |
| Output: Die schnelle braune Katze springt über den faulen Hund |
| ``` |
|
|
| Correctly handles: |
| - Adjective vs noun: "braune" (lowercase) vs "Katze" (capitalize) |
| - Formal pronouns: "Ihnen" (capitalize) |
| - Compound words and proper nouns |
|
|
| ## CRF Truecaser |
|
|
| Trained on 245K sentences of WMT News Crawl German using [python-crfsuite](https://github.com/scrapinghub/python-crfsuite). |
|
|
| - **Features**: word identity, 3-char suffix, noun suffixes, previous/next word, article context |
| - **Decode**: Viterbi over linear-chain CRF (3 labels: lc, u1, uc) |
| - **Training data**: WMT News Crawl 2023 German (8.5 MB model, MIT license) |
|
|
| ## Statistical Truecaser |
|
|
| Simple word-frequency lookup trained on WMT News Crawl 2023 German. |
|
|
| - **Entries**: 71,142 unique words |
| - **Size**: 1.7 MB |
| - **Approach**: for each word, pick the casing variant (lowercase/capitalize/uppercase) seen most often |
| - **Training data**: WMT News Crawl 2023 German (278K sentences), MIT license |
|
|
| ## Usage with CrispASR |
|
|
| ```bash |
| # BiLSTM (recommended) |
| crispasr --backend wav2vec2-de -m model.gguf --truecase-model lstm -f audio.wav |
| |
| # CRF |
| crispasr --backend wav2vec2-de -m model.gguf --truecase-model crf -f audio.wav |
| |
| # Statistical |
| crispasr --backend wav2vec2-de -m model.gguf --truecase-model auto -f audio.wav |
| |
| # Combined with punctuation restoration |
| crispasr --backend moonshine -m model.gguf --punc-model punctuate-all --truecase-model lstm -f audio.wav |
| ``` |
|
|
| ## Conversion |
|
|
| ```bash |
| # BiLSTM: download from mayhewsw, convert to binary |
| wget https://github.com/mayhewsw/pytorch-truecaser/releases/download/v1.0/wmt-truecaser-model-de.tar.gz |
| tar xzf wmt-truecaser-model-de.tar.gz |
| python models/convert-lstm-truecaser-to-bin.py --input wmt-truecaser-de/ --output truecaser-lstm-de.bin |
| |
| # CRF: train from Wikipedia |
| python models/train-truecaser-crf.py --output truecaser-crf-de.bin |
| ``` |
|
|
