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Foreign English Accent Adjustment by Learning Phonetic Patterns

Paper · 2018 · Fedor Kitashov, Elizaveta Svitanko and Debojyoti Dutta

Summary

Speech recognizers perform poorly on rare foreign accents because there is little accented training data. The authors aim to learn accent patterns automatically, instead of relying on rules written by hand by phonologists. They use the Speech Accent Archive (GMU), where speakers from many language backgrounds read the same "Please call Stella" paragraph. They align IPA transcriptions of these readings with General American English (GAE) pronunciations. For every sound, they count how often it is replaced, deleted, or has another sound inserted before or after it. These counts become probabilities, which they apply to the CMU Pronouncing Dictionary to synthesize about a million accented word transcriptions. On the detailed GMU symbol set, the statistics recover all 20 expert-listed generalizations. On the reduced CMU inventory they recover 13. A character-level seq2seq LSTM is then trained to map Russian-accented transcriptions back to standard ones, in the manner of a spell-checker, and reaches 59% accuracy. The study shows that a small set of expert transcriptions can be expanded into large synthetic training data.

Key points

  • Source data is the GMU Speech Accent Archive: 2511 recordings covering 239 ethnology codes, about half of them transcribed in IPA. The data covers 69 words of the elicitation paragraph.
  • A reduction dictionary collapses 169 distinct GMU transcription characters into the 39 sounds used by the CMU Pronouncing Dictionary.
  • Per-sound statistics include total count, replacements, deletions, and insertions before and after the sound. Multi-sound substitutions are allowed, such as [p] becoming [b@].
  • Learned generalizations match 20/20 expert features on the full GMU symbols but only 13/20 on the simplified CMU set. The CMU dictionary grows from about 103,000 single-accent entries to about one million multi-accent samples.
  • The correction model is an encoder-decoder LSTM with 256 units, trained with RMSprop, batch size 4096, for 100 epochs. Training uses about 800,000 Russian-accented samples split 80/10/10. Words up to 14 characters cover 99% of the corpus. Reported accuracy is 59%.

Interesting ideas

  • I1. Learn a per-symbol edit model (substitute, delete, insert left or right) from a handful of aligned variant/standard pairs, then sample from it to produce realistic noisy variants at scale; this is cheap and easy to interpret.
  • I2. Treat accent normalization as spelling correction, and train the corrector only on synthetic noise derived from a clean dictionary, because the small real dataset just gets memorized.
  • I3. Map a rich annotation inventory onto a coarser one, then measure explicitly which expert-known distinctions survive (20 versus 13). This makes the cost of simplification visible rather than hidden.
  • I4. Validate automatically induced rules by checking them against an independent list of rules that experts compiled by hand.

For Mova

How these ideas could serve Mova, our small open language model — its files, stages and tests:

  • I1 (tokens): Counts learned from real misspellings or nonstandard spellings could generate noisy word forms for stress-testing the tokenizer, tagger and lemmatizer, with each variant traceable to explicit edit statistics.
  • I2 (learn): Silver training data for a normalizer could be built by corrupting clean lexicon entries with learned edit probabilities, keeping real samples only for evaluation.
  • I3 (tree): When converting between UD dialects or tagsets, a checklist of linguistically known distinctions could show which ones a conversion keeps and which it erases.
  • I4 (learn): Self-induced repair rules could be scored on how many hand-written grammar facts they rediscover, giving an explainable sanity check alongside accuracy.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Fields, topics and concepts

Cite

Cite as Fedor Kitashov, Elizaveta Svitanko and Debojyoti Dutta. 2018. Foreign English Accent Adjustment by Learning Phonetic Patterns. arXiv:1807.03625.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.1807.03625 · arXiv 1807.03625

@misc{kitashov2018foreign,
  title = {{Foreign English Accent Adjustment by Learning Phonetic Patterns}},
  author = {Fedor Kitashov, Elizaveta Svitanko and Debojyoti Dutta},
  year = {2018},
  doi = {10.48550/arxiv.1807.03625},
  eprint = {1807.03625},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.1807.03625}
}

References

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