Eesen – End-to-End Speech Recognition using Deep RNN Models and WFST-based Decoding

The Eesen framework drastically simplifies the existing pipeline to build state-of-the-art ASR systems. Acoustic models in Eesen are deep bidirectional RNNs trained with the CTC objective function.

Eesen contains 4 key components to enable end-to-end ASR:

  • Acoustic Model — Bi-directional RNNs with LSTM units.
  • Training — Connectionist temporal classification (CTC) as the training objective.
  • WFST Decoding — A principled decoding approach based on Weighted Finite-State Transducers (WFSTs), or
  • RNN-LM Decoding — Decoding based on (character) RNN language models, when using Tensorflow.

Acoustic modeling in Eesen involves learning a single recurrent neural network (RNN) predicting context-independent targets (phonemes or characters). To remove the need for pre-generated frame labels, the connectionist temporal classification (CTC) objective function is adopted to infer the alignments between speech and label sequences. A distinctive feature of Eesen is a generalized decoding approach based on weighted finite-state transducers (WFSTs), which enables the efficient incorporation of lexicons and language models into CTC decoding. Experiments show that compared with the standard hybrid DNN systems, Eesen achieves comparable word error rates (WERs), while at the same time speeding up decoding significantly.

Features include:

  • The WFST-based decoding approach can incorporate lexicons and language models into CTC decoding in an effective and efficient way.
  • The RNN-LM decoding approach does not require a fixed lexicon.
  • GPU implementation of LSTM model training and CTC learning, now also using Tensorflow.
  • Multiple utterances are processed in parallel for training speed-up.
  • Fully-fledged example setups to demonstrate end-to-end system building, with both phonemes and characters as labels, following Kaldi recipes and conventions.

Developer: Yajie Miao and contributors
License: Apache License 2.0

Eesen is written in C++. Learn C++ with our recommended free books and free tutorials.

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