CREATING A SIMPLE ASR SYSTEM IN KALDI TOOLKIT FROM SCRATCH USING SMALL DIGITS CORPORA
IN OTHER WORDS: KALDI FOR DUMMIES
Author: W. Zieliński
--------------
AGENDA
--------------1. INTRODUCTION
2. ENVIRONMENT
3. DOWNLOAD KALDI
4. KALDI DIRECTORIES STRUCTURE
5. YOUR EXEMPLARY PROJECT
6. DATA PREPARATION
7. PROJECT FINALIZATION
8. RUNNING SCRIPTS CREATION
9. GETTING RESULTS
10. SUMMARY
----------------------------
1. INTRODUCTION
----------------------------This is a step by step tutorial for absolute beginners on how to create a simple ASR (Automatic Speech Recognition) system in Kaldi toolkit using your own set of data. I really would have liked to read something like this when I was starting to deal with Kaldi. This is all based on my experience as an amateur in case of speech recognition subject and script programming as well. If you have ever delved through Kaldi tutorial on the official project site and felt a little bit lost, well, my piece of art might be the choice for you. You will learn how to install Kaldi, how to make it work and how to run an ASR system using your own audio data. As an effect you will get your first speech decoding results.
First of all - get to know what Kaldi actually is and why you should use it instead of something else. In my opinion Kaldi requires solid knowledge about speech recognition and ASR systems in general. It is also good to know the basics of script languages (bash, perl, python). C++ migh be useful in the future (probably you will want to make some modifications in the source code).
To read:
http://kaldi.sourceforge.net/about.html &
http://kaldi.sourceforge.net/tutorial_prereqs.html---------------------------
2. ENVIRONMENT
---------------------------Rule number 1 - use Linux. Although it is possible to use Kaldi on Windows, most people I find trustworthy convinced me that Linux will do the job with the less amount of problems. I have chosen Ubuntu 14.10. This was (in 2014/15) a rich and stable Linux representation which I honestly recommend. When you finally have your Linux running properly, please open a terminal and install some necessary stuff (if you do not already have it):
(has to be installed)
atlas – automation and optimization of calculations in the field of linear algebra,
autoconf – automatic software compilation on different operating systems,
automake – creating portable Makefile files,
git – distributed revision control system,
libtool – creating static and dynamic libraries,
svn – revision control system (Subversion), necessary for Kaldi download and installation,
wget – data transfer using HTTP, HTTPS and FTP protocols,
zlib – data compression,
(probably has to be installed)
awk – programming language, used for searching and processing patterns in files and data streams,
bash – Unix shell and script programming language,
grep – command-line utility for searching plain-text data sets for lines matching a regular expression,
make – automatically builds executable programs and libraries from source code,
perl – dynamic programming language, perfect for text files processing.
Done. Operating system and all the necessary Linux tools are ready to go.
---------------------------------
3. DOWNLOAD KALDI
---------------------------------Just follow the instruction:
http://kaldi.sourceforge.net/install.htmlIf you do not have much idea about how to use GIT, please read about it:
http://kaldi.sourceforge.net/tutorial_git.htmlI installed Kaldi in this directory (called 'Kaldi root path'): /home/{user}/kaldi-trunk
---------------------------------------------------------
4. KALDI DIRECTORIES STRUCTURE
---------------------------------------------------------Try to acknowledge where particular Kaldi components are placed. Also it would be nice if you read any "README" files you will find.
'kaldi-trunk' - main Kaldi directory which contains:
'egs' – example scripts allowing you to quickly build ASR systems for over 30 popular speech corporas (documentation is attached for each project),
'misc' – additional tools and supplies, not needed for proper Kaldi functionality,
'src' – Kaldi source code,
'tools' – useful components and external tools,
'windows' – tools for running Kaldi using Windows.
The most important directory for you is obviously 'egs'. Here you will create your own ASR system.
--------------------------------------------------
5. YOUR EXEMPLARY PROJECT
--------------------------------------------------For the purpose of this tutorial, imagine that you have the same simple set of data as me (described below, in 6.1. AUDIO DATA section). Then try to 'transpose' every action I do straight into your own project. If you completely do not have any audio data or you want to follow my tutorial in an identical way, feel free to record your own tracks - it will be even bigger experience to play with ASR. Here we go.
YOUR PRECONDITION:
You have some amount of audio data that contain only spoken digits (zero, one, two...) by at least several different speakers. Each audio file is an entire spoken sentence (e.g. 'one, nine, five').
YOUR PURPOSE:
You want to divide your data into train and test sets, set up an ASR system, train it, test it and get some decoding results.
YOUT FIRST TASK:
Something to begin with - create a folder 'digits' in kaldi-trunk/egs/ directory. This is a place where you will put all the stuff related to your project.
------------------------------------
6. DATA PREPARATION
------------------------------------
6.1. AUDIO DATA
--------------------------I assume that you want to set up an ASR system, basing on your own audio data. For example - let it be a set of 100 files. File format is WAV. Each file contains 3 spoken numbers recorded in english language, one by one. Each of these audio files is named in a recognizable way (e.g. 1_5_6.wav, which in my pattern means that the spoken sentence is 'one, five, six') and placed in the recognizable folder representing particular speaker during a particular recording session (there may be a situation that you have recordings of the same person but in two different quality/noise environments - put these in separate folders). So to sum up, my exemplary data set looks like this:
- 10 different speakers (ASR systems must be trained and tested on different speakers, the more speakers you have the better),
- each speaker says 10 sentences,
- 100 senteces/utterances (in 100 *.wav files placed in 10 folders realted to particular speakers - 10 *.wav files in each folder),
- 300 words (digits from zero to nine),
- each sentence/utterance consist of 3 words.
Whatever your first data set is, adjust my example to your particular case. Be careful with big data sets and complex grammars - start with something simple. Sentences that contain only digits are perfect in this case.
TASK:
Go to kaldi-trunk/egs/digits directory and create 'digits_audio' folder. In kaldi-trunk/egs/digits/digits_audio create two folders: 'train' and 'test'. Select one speaker of your choice to represent testing data set. Use this speaker's 'speakerID' as a name for an another new folder in kaldi-trunk/egs/digits/digits_audio/test directory. Then put there all the audio files related to that person. Put the rest (9 speakers) into 'train' folder - this will be your training data set. Also create subfolders for each speaker.
6.2. ACOUSTIC DATA
--------------------------------Now you have to create some text files that will allow Kaldi to communicate with your audio data. Consider these files as 'must be done'.
TASK:
In kaldi-trunk/egs/digits directory, create a folder 'data'. Then create 'test' and 'train' subfolders inside. Create in each subfolder following files (so you have files named in THE SAME WAY IN 'test' AND 'train' SUBFOLDERS BUT THEY RELATE TO TWO DIFFERENT DATA SETS that you created before):
a.) spk2gender
This file informs about speakers gender. As we assumed, 'speakerID' is a unique name of each speaker (in this case it is also a 'recordingID' - every speaker has only one audio data folder from one recording session). In my example there are 5 female and 5 male speakers (f = female, m = male).
PATTERN: <speakerID> <gender>
----- exemplary spk2gender starts -----
july f
cristine f
dad m
josh m
# and so on...
----- exemplary spk2gender ends -----
b.) wav.scp
This file connects every utterance (sentence said by one person during particular recording session) with an audio file related to this utterance. If you stick to my naming approach, 'utteranceID' is nothing more than 'speakerID' (speaker's folder name) glued with *.wav file name without '.wav' ending (look for examples below).
PATTERN: <uterranceID> <full_path_to_audio_file>
----- exemplary wav.scp starts -----
july_1_2_5 /home/{user}/kaldi-trunk/egs/digits/digits_audio/train/july/1_2_5.wav
july_6_8_3 /home/{user}/kaldi-trunk/egs/digits/digits_audio/train/july/6_8_3.wav
dad_4_4_2 /home/{user}/kaldi-trunk/egs/digits/digits_audio/train/dad/4_4_2.wav
# and so on...
----- exemplary wav.scp ends -----
c.) text
This file contains every utterance matched with its text transcription.
PATTERN: <uterranceID> <text_transcription>
----- exemplary text starts -----
july_1_2_5 one two five
july_6_8_3 six eight three
dad_4_4_2 four four two
# and so on...
----- exemplary text ends -----
d.) utt2spk
This file tells the ASR system which utterance belongs to particular speaker.
PATTERN: <uterranceID> <speakerID>
----- exemplary utt2spk starts -----
july_1_2_5 july
july_6_8_3 july
dad_4_4_2 dad
# and so on...
----- exemplary utt2spk ends -----
e.) corpus.txt
This file has a slightly different directory. In kaldi-trunk/egs/digits/data create another folder 'local'. In kaldi-trunk/egs/digits/data/local create a file corpus.txt which should contain every single utterance transcription that can occur in your ASR system (in our case it will be 100 lines from 100 audio files).
PATTERN: <text_transcription>
----- exemplary corpus.txt starts -----
one two five
six eight three
four four two
# and so on...
----- exemplary corpus.txt ends -----
6.3. LANGUAGE DATA
----------------------------------This section relates to language modelling files that also need to be considered as 'must be done'. Look for the syntax details here:
http://kaldi.sourceforge.net/data_prep.html (each file is precisely described). Also feel free to read some examples in other 'egs' scripts. Now it is the perfect time.
TASK:
In kaldi-trunk/egs/digits/data/local directory, create a folder 'dict'. Then create 'test' and 'train' subfolders inside. In kaldi-trunk/egs/digits/data/local/dict create following files:
a.) lexicon.txt
This file contains every word from your dictionary with its 'phone transcriptions' (taken from /egs/voxforge).
PATTERN: <word> <phone 1> <phone 2> ...
----- exemplary lexicon.txt starts -----
!SIL sil
<UNK> spn
eight ey t
five f ay v
four f ao r
nine n ay n
one hh w ah n
one w ah n
seven s eh v ah n
six s ih k s
three th r iy
two t uw
zero z ih r ow
zero z iy r ow
----- exemplary lexicon.txt ends -----
b.) nonsilence_phones.txt
This file lists nonsilence phones that are present in your project.
PATTERN: <phone>
----- exemplary nonsilence_phones.txt starts -----
ah
ao
ay
eh
ey
f
hh
ih
iy
k
n
ow
r
s
t
th
uw
w
v
z
----- exemplary nonsilence_phones.txt ends -----
c.) silence_phones.txt
This file lists silence phones.
PATTERN: <phone>
----- exemplary silence_phones.txt starts -----
sil
spn
----- exemplary silence_phones.txt ends -----
d.) optional_silence.txt
This file lists optional silence phones.
PATTERN: <phone>
----- exemplary optional_silence.txt starts -----
sil
----- exemplary optional_silence.txt ends -----
------------------------------------------
7. PROJECT FINALIZATION
------------------------------------------Last chapter before runnig scripts creation. Your project structure will become complete.
7.1. TOOLS ATTACHMENT
----------------------------------------You need to add necessary Kaldi tools that are widely used in exemplary scripts.
TASK:
From kaldi-trunk/egs/wsj/s5 copy two folders (with the whole content) - 'utils' and 'steps' - and put them in your kaldi-trunk/egs/digits directory. You can also create links to these directories. You may find such links in, for example, kaldi-trunk/egs/voxforge/s5.
7.2. SCORING SCRIPT
----------------------------------This script will help you to get decoding results.
TASK:
From kaldi-trunk/egs/voxforge/local copy the script score.sh into exactly same location in your project (kaldi-trunk/egs/digits/local).
7.3. CONFIGURATION FILES
-------------------------------------------It is not necessary to create configuration files but it can be a good habit for future.
TASK:
In kaldi-trunk/egs/digits create a folder 'conf'. Inside kaldi-trunk/egs/digits/conf create two files (for some configuration modifications in decoding and mfcc feature extraction processes - taken from /egs/voxforge):
a.) decode.config
----- exemplary decode.config starts -----
first_beam=10.0
beam=13.0
lattice_beam=6.0
----- exemplary decode.config ends -----
b.) mfcc.conf
----- exemplary mfcc.conf starts -----
--use-energy=false
----- exemplary mfcc.conf ends -----
---------------------------------------------------
8. RUNNING SCRIPTS CREATION
---------------------------------------------------Your first ASR system written in Kaldi environment is almost ready. Your last job is to prepare running scripts to create ASR system of your choice. I put some comments in prepared scripts for ease of understanding.
These scripts are based on solution used in /egs/voxforge directory. I decided to use two different training methods:
- MONO - monophone training,
- TRI1 - simple triphone training (first triphone pass).
These two methods are enough to show noticable differences in decoding results using only digits lexicon and small training data set.
TASK:
In kaldi-trunk/egs/digits directory create 3 scripts:
a.) cmd.sh
----- cmd.sh script starts here --------------------------------------------------
# Setting local system jobs (local CPU - no external clusters)
export train_cmd=
run.plexport decode_cmd=
run.pl----- cmd.sh script ends here --------------------------------------------------
b.) path.sh
----- path.sh script starts here --------------------------------------------------
# Defining Kaldi root directory
export KALDI_ROOT=`pwd`/../..
# Setting paths to useful tools
export PATH=$PWD/utils/:$KALDI_ROOT/src/bin:$KALDI_ROOT/tools/openfst/bin:$KALDI_ROOT/src/fstbin/:$KALDI_ROOT/src/gmmbin/:$KALDI_ROOT/src/featbin/:$KALDI_ROOT/src/lm/:$KALDI_ROOT/src/sgmmbin/:$KALDI_ROOT/src/sgmm2bin/:$KALDI_ROOT/src/fgmmbin/:$KALDI_ROOT/src/latbin/:$PWD:$PATH
# Defining audio data directory (modify it for your installation directory!)
export DATA_ROOT="/home/{user}/kaldi-trunk/egs/digits/digits_audio"
# Variable that stores path to MITLM library
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(pwd)/tools/mitlm-svn/lib
# Variable needed for proper data sorting
export LC_ALL=C
----- path.sh script ends here --------------------------------------------------
c.) run.sh
----- run.sh script starts here --------------------------------------------------
#!/bin/bash
. ./path.sh || exit 1
. ./cmd.sh || exit 1
nj=1 # number of parallel jobs - 1 is perfect for such a small data set
lm_order=1 # language model order (n-gram quantity) - 1 is enough for digits grammar
# Safety mechanism (possible running this script with modified arguments)
. utils/parse_options.sh || exit 1
[[ $# -ge 1 ]] && { echo "Wrong arguments!"; exit 1; }
# Removing previously created data (from last run.sh execution)
rm -rf exp mfcc data/train/spk2utt data/train/cmvn.scp data/train/feats.scp data/train/split1 data/test/spk2utt data/test/cmvn.scp data/test/feats.scp data/test/split1 data/local/lang data/lang data/local/tmp data/local/dict/lexiconp.txt
echo
echo "===== PREPARING ACOUSTIC DATA ====="
echo
# Needs to be prepared by hand (or using self written scripts):
#
# spk2gender [<speaker-id> <gender>]
# wav.scp [<uterranceID> <full_path_to_audio_file>]
# text [<uterranceID> <text_transcription>]
# utt2spk [<uterranceID> <speakerID>]
# corpus.txt [<text_transcription>]
# Making spk2utt files
utils/
utt2spk_to_spk2utt.pl data/train/utt2spk > data/train/spk2utt
utils/
utt2spk_to_spk2utt.pl data/test/utt2spk > data/test/spk2utt
echo
echo "===== FEATURES EXTRACTION ====="
echo
# Making feats.scp files
mfccdir=mfcc
# utils/validate_data_dir.sh data/train # script for checking if prepared data is all right
# utils/fix_data_dir.sh data/train # tool for data sorting if something goes wrong above
steps/make_mfcc.sh --nj $nj --cmd "$train_cmd" data/train exp/make_mfcc/train $mfccdir
steps/make_mfcc.sh --nj $nj --cmd "$train_cmd" data/test exp/make_mfcc/test $mfccdir
# Making cmvn.scp files
steps/compute_cmvn_stats.sh data/train exp/make_mfcc/train $mfccdir
steps/compute_cmvn_stats.sh data/test exp/make_mfcc/test $mfccdir
echo
echo "===== PREPARING LANGUAGE DATA ====="
echo
# Needs to be prepared by hand (or using self written scripts):
#
# lexicon.txt [<word> <phone 1> <phone 2> ...]
# nonsilence_phones.txt [<phone>]
# silence_phones.txt [<phone>]
# optional_silence.txt [<phone>]
# Preparing language data
utils/prepare_lang.sh data/local/dict "<UNK>" data/local/lang data/lang
echo
echo "===== LANGUAGE MODEL CREATION ====="
echo "===== MAKING lm.arpa ====="
echo
loc=`which ngram-count`;
if [ -z $loc ]; then
if uname -a | grep 64 >/dev/null; then
sdir=$KALDI_ROOT/tools/srilm/bin/i686-m64
else
sdir=$KALDI_ROOT/tools/srilm/bin/i686
fi
if [ -f $sdir/ngram-count ]; then
echo "Using SRILM language modelling tool from $sdir"
export PATH=$PATH:$sdir
else
echo "SRILM toolkit is probably not installed.
Instructions: tools/install_srilm.sh"
exit 1
fi
fi
local=data/local
ngram-count -order $lm_order -write-vocab $local/tmp/vocab-full.txt -wbdiscount -text $local/corpus.txt -lm $local/tmp/lm.arpa
echo
echo "===== MAKING G.fst ====="
echo
lang=data/lang
cat $local/tmp/lm.arpa | arpa2fst - | fstprint | utils/
eps2disambig.pl | utils/
s2eps.pl | fstcompile --isymbols=$lang/words.txt --osymbols=$lang/words.txt --keep_isymbols=false --keep_osymbols=false | fstrmepsilon | fstarcsort --sort_type=ilabel > $lang/G.fst
echo
echo "===== MONO TRAINING ====="
echo
steps/train_mono.sh --nj $nj --cmd "$train_cmd" data/train data/lang exp/mono || exit 1
echo
echo "===== MONO DECODING ====="
echo
utils/mkgraph.sh --mono data/lang exp/mono exp/mono/graph || exit 1
steps/decode.sh --config conf/decode.config --nj $nj --cmd "$decode_cmd" exp/mono/graph data/test exp/mono/decode
echo
echo "===== MONO ALIGNMENT ====="
echo
steps/align_si.sh --nj $nj --cmd "$train_cmd" data/train data/lang exp/mono exp/mono_ali || exit 1
echo
echo "===== TRI1 (first triphone pass) TRAINING ====="
echo
steps/train_deltas.sh --cmd "$train_cmd" 2000 11000 data/train data/lang exp/mono_ali exp/tri1 || exit 1
echo
echo "===== TRI1 (first triphone pass) DECODING ====="
echo
utils/mkgraph.sh data/lang exp/tri1 exp/tri1/graph || exit 1
steps/decode.sh --config conf/decode.config --nj $nj --cmd "$decode_cmd" exp/tri1/graph data/test exp/tri1/decode
echo
echo "===== run.sh script is finished ====="
echo
----- run.sh script ends here --------------------------------------------------
----------------------------------
9. GETTING RESULTS
----------------------------------TASK:
Now all you have to do is to run run.sh script. If I have made any mistakes in this tutorial, logs from the terminal should guide you how to deal with it.
Besides the fact that you will notice some decoding results in the terminal window, go to newly made 'kaldi-trunk/egs/digits/exp'. You may notice there folders with 'mono' and 'tri1' results as well - directories structure are the same. Got to 'mono/decode' directory. Here you may find result files (named in a 'wer_{number}' way). Logs for decoding process may be found in 'log' folder (same directory).
----------------------
10. SUMMARY
----------------------This is just an example. The point of this short tutorial is to show you how to create 'anything' in Kaldi and to get a better understanding of how to think while using this toolkit. Personally I started with looking for tutorials made by the Kaldi authors/developers. After succesful Kaldi installation I launched some example scripts (Yesno, Voxforge, LibriSpeech - they are relatively easy and have free acoustic/language data to download - I used these three as a base for my own scripts).
Make sure you follow
http://kaldi.sourceforge.net/index.html (now moving to
http://kaldi-asr.org/) - official project website. There are two very useful sections for beginners inside:
a.)
http://kaldi.sourceforge.net/tutorial.html - almost 'step by step' tutorial on how to set up an ASR system; up to some point this can be done without RM dataset. It is good to read it,
b.)
http://kaldi.sourceforge.net/data_prep.html - very detailed explaination of how to use your own data in Kaldi.
More useful links about Kaldi I found:
https://sites.google.com/site/dpovey/kaldi-lectures - Kaldi lectures created by the main author
http://www.superlectures.com/icassp2011/category.php?lang=en&id=131 - similar; video version
http://www.diplomovaprace.cz/133/thesis_oplatek.pdf - some master diploma thesis about speech recognition using Kaldi
---
This is all from my side. Good luck!