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Speech Recognition System Comparison: Microsoft vs IBM 2016

Just a quick comparison between the two very interesting articles.

This article compares the IBM 2016 Speech Recognition Systems (article: The IBM 2016 English Conversational Telephone Speech Recognition System by G Saon etc. a.k.a ISR2016) and the Microsoft 2016 Speech Recognition Systems (article: The Microsoft 2016 Conversational Speech Recognition Systems by W Xiong etc. a.k.a. MSR2016). I have also previously wrote about the Microsoft paper here.

Data Extraction and Preprocessing

Data Extraction: same. 25ms analysis frame and 10ms frame-shift.

Data Processing:

MSR2016: log-filterbank features extracted

ISR2016:

Speaker Adaptation Model:

MSR2016: 100 dimension i-vector

ISR2016: 100 dimension i-vector, VTL, PLP etc.

Data Source

Training Data:

ISR2016:

  • SwitchBoard 1: 262 hours
  • Fisher: 1698 hours
  • CallHome: 15 hours

MSR2016 Acoustic Training Data:

  • Switchboard-1 Release 2 (LDC 97S62)
  • Fisher English Training Speech Part 1 Speech (LDC 2004S13)
  • Fisher English Training Part 2, Speech (LDC 2005S13)
  • 2002 Rich Transcription Broadcast News and Conversational Telephone Speech (LDC 2004S11)
  • NIST Meeting Pilot Corpus Speech (LDC 2004S09)

MSR2016 Language Training Data: CTS transcripts from the DARPA EARS program:

  • Switchboard (3M words),
  • BBN Switchboard-2 transcripts (850k),
  • Fisher (21M),
  • English CallHome (200k),
  • the University of Washington conversational Web corpus (191M).

Testing Data:

ISR2016 - Hub5 2000:

  • SwitchBoard Data: 2.1 hours with 21.4K words and 40 speakers
  • CallHome Data: 1.6 hours with 21.6K words and 40 speakers

MSR2016 appears to use CallHome and Switchboard testing data. Not specified in the article.

Acoustic Model Training

ISR2016:

  • Recurrent nets with maxout activations trained with Hessian-free sequence discriminative training
  • Very deep convolutional networks: similar to VGG: cross-entropy training + NAG?
  • Bidirectional LSTM

MSR2016:

  • CNN variant — VGG
  • CNN variant — Residual Net
  • CNN variant — LACE (layer-wise context expansion with attention) model
  • Bidirectional LSTM

MSR2016 uses cross-entropy training plus lattice-free maximum mutual information (LFMMI) training.

Language Model Training

ISR2016:

  • vocabulary size is 85K
  • trained a 4-gram model with modified Kneser-Ney smoothing
  • linearly interpolated with weights chosen to optimize perplexity on a held-out set
  • Entropy pruning
  • LM Rescoring: model M (a class-based exponential model) and feed-forward neural network LM (NNLM)

MSR2016:

An initial decoding is done with a WFST decoder, using the architecture described in [31]. We use an N-gram language model trained and pruned with the SRILM toolkit [32]. The first-pass LM has approximately 15.9 million bigrams, trigrams, and 4grams, and a vocabulary of 30500 words. and gives a perplexity of 54 on RT-03 speech transcripts. The initial decoding produces a lattice with the pronunciation variants marked, from which 500-best lists are generated for rescoring purposes. Subsequent N-best rescoring uses an unpruned LM comprising 145 million N-grams. All N-gram LMs were estimated by a maximum entropy criterion as described in [33].

CUED-RNNLM toolkit is used to train and score various LM RNNs: forward predicting RNNLM and backward RNNLM.

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