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Joint Modeling of Accents and Acoustics for Multi-Accent Speech Recognition

Paper · 2018 · Xuesong Yang, Kartik Audhkhasi, Andrew Rosenberg et al.

Summary

Speech recognizers lose accuracy when test speakers have an accent that differs from the training data. Earlier multi-accent acoustic models relied on accent information only indirectly, for example through separate phone sets per accent. Yang et al. instead train an accent identification (AID) network together with a multi-task acoustic model. Both are built on bidirectional LSTMs. The acoustic part uses CTC loss, with shared lower layers and a separate DNN output branch for each accent. The AID part pools frame representations into one utterance-level decision. In the joint model, AID serves as an auxiliary objective on the lower layers, and the two losses are mixed with a tuned weight. At test time, the AID output acts as a hard switch that picks which accent-specific output layer to use. On the WSJ American English and Cambridge British English corpora, the joint model beats a strong multi-task baseline, with relative WER gains of 5.94% on British and 9.47% on American English. Accent identification also improves under joint training. The work suggests that explicit accent supervision helps acoustic modeling.

Key points

  • Data: WSJ-1 (American English) and Cambridge (British English), about 15 hours each. Their phone inventories overlap but differ, with 42 and 45 phones. 5% of the training data was held out for development.
  • Features: 40-dimensional log-Mel filter banks with per-utterance cepstral mean subtraction and no VTLN. Neighbouring frames are stacked into 80-dimensional vectors at half the frame rate.
  • The AID model uses BLSTMs, DNN projections and average pooling, with a single sigmoid output for US vs UK. It is trained with cross-entropy and thresholded at 0.5 to select the output head.
  • Joint objective: (1−α)·L_AM (CTC) + α·L_AID (cross-entropy). Because the two losses sit on different scales, α is tuned on development data.
  • Results: relative WER reductions of 5.94% (UK) and 9.47% (US) over the multi-task AM. The switch was tested with both oracle and predicted accent labels.

Interesting ideas

  • I1. Supervise the lower layers with an auxiliary "which variety is this?" task while the main task sits higher, so shared layers explicitly encode variety rather than discovering it on their own.
  • I2. Keep one shared trunk with separate variety-specific output heads, and let a visible classifier decision choose the head for each input. The choice is a discrete, inspectable step rather than a hidden blend.
  • I3. When the evidence for a property is not present at every position, pool over the whole sequence before classifying instead of deciding locally.
  • I4. When two losses on different scales are combined, treat the mixing weight as a tuned hyperparameter selected on held-out data rather than fixing it at 0.5.
  • I5. Evaluate the pipeline with both the gold (oracle) upstream decision and the predicted one, so the cost of upstream errors is measured separately.

For Mova

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

  • I1 (tree): gparse could add a treebank/genre-source classifier on its lower encoder layers, which would help it separate UD dialect conventions before predicting arcs.
  • I2 (tree): treebank-specific arc/label heads could be selected by a predicted source label, and that label logged so every parse states which convention it followed.
  • I3 (tokens): register or variety detection (e.g., British vs American spelling, informal text) could pool over all tokens of a sentence or document before choosing lemmatization or spelling rules.
  • I4 (learn): multi-objective training of the parser (arcs, labels, auxiliary tags) could tune its weights on a dev split alongside the negative-control evaluation.
  • I5 (learn): run frames and answer evaluations once on gold UD trees and once on predicted trees, to attribute failures to the correct stage.

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

 Institutions

 Fields, topics and concepts

Cite

Cite as Xuesong Yang, Kartik Audhkhasi, Andrew Rosenberg, Samuel Thomas, Bhuvana Ramabhadran and Mark Hasegawa-Johnson. 2018. Joint Modeling of Accents and Acoustics for Multi-Accent Speech Recognition. arXiv:1802.02656.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.1802.02656 · arXiv 1802.02656

@misc{yang2018joint,
  title = {{Joint Modeling of Accents and Acoustics for Multi-Accent Speech Recognition}},
  author = {Xuesong Yang, Kartik Audhkhasi, Andrew Rosenberg, Samuel Thomas, Bhuvana Ramabhadran and Mark Hasegawa-Johnson},
  year = {2018},
  doi = {10.48550/arxiv.1802.02656},
  eprint = {1802.02656},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.1802.02656}
}

References

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