Hello Everyone,
Today I’m going to tell you how to expand dictionary of acoustic model for Sphinx4. In simple words, This tutorial will tell you how you can add more words in Sphinx’s words database (Dictionary) and let it recognize those words, which are not available in default acoustic models provided by CMU Sphinx. This tutorial is based on “HelloWorld” example provided by CMU Sphinx.
Important Files in this example :
1 ) HelloWorld.java
2) hello.gram
3) helloworld.config.xml
Acoustic Model used in this example :
WSJ_8gau_13dCep_16k_40mel_130Hz_6800Hz.jar
Lets say, We are creating a SR system for ABC National airlines. Everything will go fine and Sphinx will recognize most of the words except the name of cities and states of India. Now, I will tell you, How to add name of cities and states in dictionary.
PART ONE
Step 1 : Create a txt file “words.txt”, Write all the names of cities and states in it and save.
Step 2 : Open this link : http://www.speech.cs.cmu.edu/tools/lmtool.html
Step 3 : On that page, go to “Sentence corpus file:” section, Browse to “words.txt” file and click “Compile Knowledge Base”.
Step 4 : On next page, Click on “Dictionary” link and save that .DIC file.
PART TWO
Step 1 : Extract WSJ_8gau_13dCep_16k_40mel_130Hz_6800Hz.jar file.
Step 2 : Go to edu\cmu\sphinx\model\acoustic\WSJ_8gau_13dCep_16k_40mel_130Hz_6800Hz\dict folder.
Step 3 : Open “cmudict.0.6d” file in that folder.
Step 4 : Copy data from .DIC file, you have downloaded in PART ONE, paste it in “cmudict.0.6d” file and save.
Step 5 : Zip the extracted hierarchy back as it was and Zip file named should be same as JAR file.
Now, remove “WSJ_8gau_13dCep_16k_40mel_130Hz_6800Hz.jar” file from Project’s CLASSPATH and add “WSJ_8gau_13dCep_16k_40mel_130Hz_6800Hz.zip” instead of it.
That’s it ! We are done. Now Sphinx will also recognize all name of cities and states that we wrote in “words.txt” file.
Now, FAQ time. I will be posting FAQ and few important notes in comments. 
If you have any quires, Please feel free to ask.
Regards,