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Support hotword boosting feature and lexicon based decoding #222

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@Sushmitha-Deva Sushmitha-Deva commented Nov 16, 2023

This pull request includes modifications that enable hotword boosting, lexicon-based decoding, and the build configuration for the ctcdecode library.

Hotword boosting:

  • This feature is supported for both character and wpe based (allowed characters a-z and an apostrophe) ASR labels.
  • Scoring logic for hotwords is inspired from the pyctcdecode package, where partial weight will be added to the path score containing the hotword tokens, and in case a complete hotword is not formed, it will reset the score to the original.
  • Tests for using this feature is added in this PR

Lexicon based decoding:

  • Lexicon based decoding ensures to penalize the path that's going to form an invalid word, thereby giving priority to paths containing valid spellings
  • During decoding, it compares the beam path with the lexicon FST and then applies penality for unknown path formation.
  • A constant negative value unk_score will be used as a penalty.
  • Results indicate a 90% reduction in spelling mistakes after applying this decoding. Increase in unk_score, will lead to a 100% reduction.
  • Create the lexicon FST using the build_fst tool . See tools/README.md for usage

@Sushmitha-Deva Sushmitha-Deva changed the title Support hotword boosting feature Support hotword boosting feature and lexicon based decoding Nov 18, 2023
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