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B.2 Acronyms

AENN Auto-Encoder Neural Network ASR Automatic Speech Recognition

BAMA Buckwalter Arabic Morphological Analyzer

BC Broadcast Conversation

BIC Bayesian Information Criterion

bMMI boosted Maximum Mutual Information

BN Broadcast News

CD Contrastive Divergence

CER Character Error Rate

CLM Class-based Language Model

CMLLR Constrained Maximum Likelihood Linear Regression

CN Confusion Network

CRP Chinese Restaurant Process

DARPA Defense Advanced Research Projects Agency

DAT Dialog Act Tagging

DMC Discriminative Model Combination

DNN Deep Neural Network

DNNLM Deep Neural Network Language Model

DP Dynamic Programming

DT Discriminative Training

EA Evolutionary Algorithms

ECA Egyptian Colloquial Arabic

EM Expectation Maximization

EPPS European Parliament Plenary Sessions

FFT Fast Fourier Transform

FLM Factored Language Model

fMLLR f eature space Maximum Likelihood Linear Regression G2P Grapheme-to-Phoneme Conversion

GA Genetic Algorithm

GD Graph Density

GER Graph Error Rate

GMLM Gaussian Mixture Language Model

GMM Gaussian Mixture Model

GPB Generalized Parallel Backoff

GT Gammatone filter

HCRP Hierarchical Chinese Restaurant Process HLDA Heteroscedastic Linear Discriminant Analysis

HMM Hidden Markov Model

HPY Hierarchical Pitman-Yor

HPYCLM Hierarchical Pitman-Yor Class-based Language Model HPYLM Hierarchical Pitman-Yor Language Model

IBM International Business Machines Corporation

Appendix B Symbols and Acronyms

IKN Interpolated Kneser-Ney Smoothing

KN Kneser-Ney Smoothing

LDA Linear Discriminant Analysis

LM Language Model

LSA Latent Semantic Analysis

LSTM Long Short-Term Memory Neural Network LSTMLM Long Short-Term Memory Language Model LVCSR Large Vocabulary Continuous Speech Recognition

MADA Morphological Analyzer and Disambiguator tool for Arabic

MAP Maximum A-posterior

MDL Minimum Description Length

MFCC Mel-Frequency Cepstral Coefficients

MKN Modified Kneser-Ney

ML Maximum Likelihood

MLLR Maximum Likelihood Linear Regression MLP Multilayer Perceptron Neural Network

MPE Minimum Phone Error

MSA Modern Standard Arabic

MSE Mean Square Error

MT Machine Translation

NER N-best Error Rate

NNLM Neural Network Language Model

OOV Out-Of-Vocabulary

PER Phoneme Error Rate

PLP Perceptual Linear Predictive features

POI Probability Of Improvement

POS Part-Of-Speech

PPL Perplexity

PY Pitman-Yor

RBM Restricted Boltzmann Machines

RNN Recurrent Neural Network

RNNLM Recurrent Neural Network Language Model RWTH Rheinisch Westf¨alische Technische Hochschule

SAT Speaker Adaptive Training

SNN Shallow Neural Network

SNNLM Shallow Neural Network Language Model SRILM SRI Language Modeling Toolkit

STC Semi-Tied Covariance

SVD Singular Value Decomposition

TC Telephone Conversations

TDP Time Distortion Penalty

TMLM Tied-Mixture Language Model

TMLM-CO Tied-Mixture Language Model with bigram CO-occurrence based features TMLM-NN Tied-Mixture Language Model with Neural Network based features

B.2 Acronyms

VTLN Vocal Tract Length Normalization

WER Word Error Rate

WFST Weighted Finite State Transducer

WSJ Wall Street Journal

List of Figures

1.1 Basic architecture of a statistical automatic speech recognition system according to [Ney 1990]. . . 3 1.2 6-state hidden Markov model in Bakis topology for the triphone sehv in the word “seven”

and the resulting trellis for a time alignment. The HMM segments are denoted by <1>,

<2>, and <3>. . . 6 1.3 An example of a word lattice (taken from [Schwenk 2007]). The lattice is produced using

a trigram LM, where each word has a unique bigram context. For simplicity, acoustic and language model scores are not shown on arcs ([fw]: filler word; [breath]: breath noise). . . 11 1.4 An example of a confusion network (CN) derived from a lattice. The figure shows: the

original lattice, a derived CN, and an intermediate lattice in which all paths have the same length. The positions for the insertions of the -arcs are derived from the CN according to the algorithm described in [Hoffmeister 2011]. The number that appears on each arc corresponds to the CN slot to which the arc is assigned. . . 12 3.1 Optimization of the number of full-words retained in the sub-word based vocabularies. . . . 42 3.2 Optimization of the overall vocabulary sizes for full-word and sub-word based experiments. 43 3.3 The best sub-word based experiments compared to the best full-word based experiments

on Arabic, German, and Polish corpora. . . 44 4.1 (a) An example of a general backoff graph showing all possible backoff paths from top to

bottom. (b) An example of a backoff graph where only a subset of the possible backoff paths are allowed. . . 57 4.2 Topologies of the Arabic FLMs using the format specifications of the SRILM-FLM

exten-sions (W: word; M: morph; L: lexeme; P: pattern). . . 62 4.3 Backoff graphs for AR−F LM1∶5, detailed topologies are given in Figure 4.2 (W: word; M:

morph; L: lexeme; P: pattern). . . 63 4.4 Topologies of the German FLMs using the format specifications of the SRILM-FLM

exten-sions (W: word; L: lexeme; I: class-index; P: POS-tag). . . 65 4.5 Backoff graphs for GR−F LM1∶7, detailed topologies are given in Figure 4.4 (W: word; L:

lexeme; I: class-index; P: POS-tag). . . 66 4.6 Comparison of recognition WERs [%] on Arabic and German corpora using different LMs. 73 4.7 Interpolation weights of individual Arabic morpheme-based LMs, models with negligible

weights are not shown in the figure. . . 74 4.8 Interpolation weights of individual German morpheme-based LMs, models with negligible

weights are not shown in the figure. . . 75 5.1 Architecture of a shallow NNLM (SNNLM) that estimates the model p(wn∣wnn−1−m+1). . . 81 5.2 Architecture of a deep NNLM (DNNLM) that estimates the model p(wn∣wnn−1−m+1). . . 82 5.3 Architecture of a deep NNLM (DNNLM) with input classes. The input encoding uses

sep-arate vectors for words and their classes for every history position. The network estimates the model p(wn∣wn−1cn−1wn−2cn−2). . . 83 5.4 Architecture of a deep NNLM (DNNLM) with input classes. The input encoding uses

one combined vector for each word and its class for every history position. The network estimates the model p(wn∣wn−1cn−1wn−2cn−2). . . 84 5.5 General steps of a greedy layer-wise unsupervised pre-training algorithm. . . 88

List of Figures

5.6 Optimization of the number of decomposable full-words retained in the morpheme-based vocabulary performed over eca-dev corpus using overall vocabulary size of 250k (best WER

= 56.8% with 5k full-words). Baseline WER on eca-dev using 350k full-words vocabulary

= 56.9%. . . 93 5.7 Comparison of recognition WERs [%] on Egyptian Arabic eca-eval corpus using different

LMs. . . 94 5.8 Interpolation weights of individual morpheme-based LMs. . . 95

List of Tables

1.1 Different Arabic words derived from the same root “ktb”. . . 15

3.1 Arabic solar and lunar consonants (bw: using Buckwalter transliteration; ar: using Arabic script). . . 31

3.2 An example of the alignment process for the word-pronunciation pair (phase,feIz). . . 35

3.3 Recognition experiments on Arabic corpora using morpheme-based LMs with 70k vocabu-laries. . . 35

3.4 Recognition experiments on Arabic corpora using full-words, morphemes, and diacritized morphemes for LMs with very large vocabularies. . . 36

3.5 word- and character-level perplexities for full-word and sub-word based LMs on Arabic corpora (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol). . . 37

3.6 Recognition experiments on German corpora using morpheme-based LMs with 100k vo-cabularies. . . 37

3.7 Recognition experiments on German corpora using 100k full-words as a baseline vocabulary and adding different fragment-based and morpheme-based graphones. . . 38

3.8 Recognition experiments on German corpora using full-words, morphemes, and morphemic graphones for LMs with very large vocabularies. . . 39

3.9 word- and character-level perplexities for full-word and sub-word based LMs on German corpora (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol). . . 39

3.10 Recognition experiments on Polish corpora using morpheme- and syllable-based LMs with 300k vocabularies. . . 40

3.11 Recognition experiments on Polish corpora using full-words, syllables, and syllabic gra-phones for LMs with very large vocabularies. . . 41

3.12 word- and character-level perplexities for full-word and sub-word based LMs on Polish corpora (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol). . . 41

3.13 Analysis of improvements in the best sub-word based system compared to the best full-word based system for Arabic, German, and Polish corpora. Amount of reduction in WER is divided into (ins: reduction in insertion rate; OOV del/sub: reduction in deletion/-substitution rate of OOV words; INV del/sub: reduction in deletion/deletion/-substitution rate of INV words). Note: a negative reduction means an increase. . . 45

3.14 Examples of words for which recognition is improved using the best sub-word based systems. 45 3.15 List of participants in different evaluation campaigns. . . 46

3.16 Quaero German ASR evaluation 2010. . . 46

3.17 Quaero German ASR evaluation 2011. . . 47

3.18 Quaero German ASR evaluation 2012. . . 47

3.19 Quaero Polish ASR evaluation 2012. . . 47

3.20 Quaero German ASR evaluation 2013. . . 47

3.21 IWSLT German ASR evaluation 2013. . . 48

3.22 OpenHaRT Arabic handwriting recognition evaluation 2013. . . 48

4.1 Recognition experiments on Arabic ar-tune07 corpus using different factored LMs (vocab-ulary: 70k full-words, OOV rate = 3.6%, N-best size = 1000, N-best error rate (NER) = 7.3%; W: word; M: morph; L: lexeme; P: pattern). . . 63

List of Tables

4.2 Perplexities for the German FLMs GR −F LM1∶7 measured on the German gr-dev09 cor-pus. Exact FLM topologies are given in Figures 4.4 and 4.5 (word-based: 100k full-words vocab; morpheme-based: 100k morpheme-based vocab with 5k full-words + 95k mor-phemes; W: word; L: lexeme; I: class-index; P: POS-tag). . . 64 4.3 Recognition WERs [%] on German corpora using different factored LMs (N-best size =

1000; word-based: 100k full-words, OOV rate = [gr-dev09: 5.0%, gr-eval09: 4.8%], N-best error rate (NER) = [gr-dev09: 23.6%, gr-eval09: 21.4%]; morpheme-based: 5k full-words + 95k morphemes, OOV rate = [gr-dev09: 1.5%, gr-eval09: 1.4%], N-best error rate (NER) = [gr-dev09: 20.0%, gr-eval09: 18.8%]). . . 67 4.4 Recognition WERs [%] on Arabic ar-dev07 corpus using stream- and class-based LMs built

over words and morphemes (N-best size = 1000; word-based: 70k full-words, OOV rate

= 3.7%, N-best error rate (NER) = 9.5%; morpheme-based: 20k full-words + 50k mor-phemes, OOV rate = 1.4%, N-best error rate (NER) = 8.2%). . . 67 4.5 Recognition experiments on Arabic corpora using class-based LMs, factored LM (AR −

F LM4), and hierarchical Pitman-Yor LMs built over words (vocabulary: 750k full-words; OOV rate = [ar-dev07: 0.5%, ar-eval07: 0.7%]; N-best size = 1000; N-best error rate (NER) = [ar-dev07: 7.6%, ar-eval07: 9.1%]). . . 68 4.6 Word- and character-level perplexities on Arabic corpora for LMs that utilize word-level

classes (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol). . . 68 4.7 Recognition experiments on Arabic corpora using class-based LMs, factored LM (AR −

F LM4), and hierarchical Pitman-Yor LMs built over morphemes (vocabulary: 20k full-words + 236k morphemes; OOV rate = [ar-dev07: 0.5%, ar-eval07: 0.7%]; N-best size = 1000; N-best error rate (NER) = [ar-dev07: 7.6%, ar-eval07: 8.8%]). . . 69 4.8 Morpheme- and character-level perplexities on Arabic corpora for LMs that utilize

morpheme-level classes (inv: perplexity for in-vocabulary text excluding the unk symbol; all: per-plexity for the whole text including the unk symbol). . . 69 4.9 Number of instances of every class for Arabic vocabularies. . . 69 4.10 Recognition WERs [%] on German corpora using stream- and class-based LMs built over

words and morphemes (N-best size = 1000; word-based: 100k full-words, OOV rate = [gr-dev09: 5.0%, gr-eval09: 4.8%], N-best error rate (NER) = [gr-dev09: 23.6%, gr-eval09:

21.4%]; morpheme-based: 5k full-words + 95k morphemes, OOV rate = [gr-dev09: 1.5%, gr-eval09: 1.4%], N-best error rate (NER) = [gr-dev09: 20.0%, gr-eval09: 18.8%]). . . 70 4.11 Recognition experiments on German corpora using class-based LMs, factored LM (GR −

F LM5), and hierarchical Pitman-Yor LMs built over words (vocabulary: 750k full-words; OOV rate = [gr-dev09: 2.3%, gr-eval09: 2.1%]; N-best size = 1000; N-best error rate (NER) = [gr-dev09: 20.6%, gr-eval09: 18.9%]). . . 71 4.12 Word- and character-level perplexities on German corpora for LMs that utilize word-level

classes (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol). . . 71 4.13 Recognition experiments on German corpora using class-based LMs, factored LM (GR −

F LM5), and hierarchical Pitman-Yor LMs built over morphemes (vocabulary: 5k full-words + 495k morphemes; OOV rate = [gr-dev09: 0.9%, gr-eval09: 0.7%]; N-best size = 1000; N-best error rate (NER) = [gr-dev09: 19.1%, gr-eval09: 17.3%]). . . 72 4.14 Morpheme- and character-level perplexities on German corpora for LMs that utilize

morpheme-level classes (inv: perplexity for in-vocabulary text excluding the unk symbol; all: per-plexity for the whole text including the unk symbol). . . 72 4.15 Number of instances of every class for German vocabularies. . . 73 5.1 Recognition experiments on CallHome Egyptian colloquial Arabic (ECA) evaluation corpus

eca-eval using word-based neural network LMs (NNLMs) for lattice rescoring. vocabulary:

350k full-words, OOV rate = 1.4%, graph (lattice) error rate (GER) = 37.2%. . . 92

List of Tables

5.2 Recognition experiments on CallHome Egyptian colloquial Arabic (ECA) evaluation cor-pus eca-eval using morpheme-based neural network LMs (NNLMs) for lattice rescoring.

vocabulary: 250k (5k words + 245k morphemes), OOV rate = 0.9%, graph (lattice) error rate (GER) = 32.3%. . . 93 5.3 Word-/morpheme-level and character-level perplexities on CallHome Egyptian colloquial

Arabic (ECA) evaluation corpus eca-eval for different LMs (inv: perplexity for in-vocabulary text excluding the unk symbol; all: perplexity for the whole text including the unk symbol;

units: words or morphemes). . . 94 A.1 Experimental corpora for: modern standard Arabic, German, Polish, and Egyptian

collo-quial Arabic. BN: broadcast news; BC: broadcast conversation; EPPS: European parlia-ment plenary sessions; PC: Podcast; TC: Telephone Conversations. . . 103

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