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  The Automatic Speech Recognition engine is used to convert speech to text. It is an alternative User Interface to DTMF in IVR applications.


 Click here to expand Table of Contents


Automated Speech Recognition is currently available via mod_pocketsphinx and mod_unimrcp.

Engines from the following vendors have been evaluated.


Nuance is the monopolistic supplier of speech recognition engines. Accuracy and performance are good but cost is prohibitively high for most applications. The SDK is free trial for 2 months. Cost of per port perpetual license varies from $800 - $2000 depending on vocabulary size and natural language. Indian English and Hindi are good. Other Indian languages are available but need to be evaluated for accuracy.




 CentOS 5.5 x86_64


 tar xvzf NRec-9.0.19-i386-rhel3.tar.gz
 tar xvzf NRec-9.0.1-en-IN.i386-rhel3.tar.gz
 tar xvzf NRec-9.0.1-hi-IN.i386-rhel3.tar.gz
 rpm -ivh NRec-en-IN-9.0-1.i386-rhel3.rpm
 rpm -ivh NRec-hi-IN-9.0-1.i386-rhel3.rpm

License Manager

 yum -y install redhat-lsb
 tar xvzf NLICMGR-11.7.0-x86_64-linux.tar.gz
 cd Nuance_License_Manager
 cd /usr/local/Nuance/license_manager/license
 cp /root/eval-rec-9.lic .
 cd ../components
 ./ /usr/local/Nuance/license_manager/license/eval-rec-9.lic

Check that the license log file /usr/local/Nuance/license_manager/license/nuance-lic.log has the following contents, which means that the evaluation license file has been correctly configured by the License Manager.

 19:55:22 (lmgrd) License file(s): /usr/local/Nuance/license_manager/license/eval-rec-9.lic
 19:55:22 (lmgrd) lmgrd tcp-port 27000
 19:55:22 (lmgrd) Starting vendor daemons ...

Check that the Nuance License Manager is running.

Nuance License Manager


Start and Test Speech Server

 service NSSservice start

Check that Nuance client is able to talk to Nuance Speech Server from a different machine.


Nuance Recognizer logs are in /usr/local/Nuance/Recognizer/data

mod_unimrcp configuration

cat conf/mrcp_profiles/nuance-5.0-mrcp-v2.xml




cat conf/autoload_configs/unimrcp.conf.xml



Sample Lua IVR

In dialplan conf/dialplan/default.xml put the following extension

Dialplan Example


cat scripts/names.lua

Lua ASR Script


Sample English Grammar

cat grammar/sr.gram

English Grammar File

Sample Hindi Grammar

cat grammar/test.gram

Hindi Grammar File


Started off from Sphinx, the free and open source project at CMU but considerable proprietary development has been done for MRCP and acoustic modelling. Indian English and Hindi are available but the cost of SDK is around $4000, so evaluation looks expensive.


Vestec provides SDK for $25 or free evaluation. Per port license fee is around $200. Indian English and Hindi are available and to be evaluated.


Simmortel uses a mix of open source and proprietary product to deliver good accuracy for medium vocabulary applications in Indian English and Hindi. However, MRCP is not available and CPU usage for concurrent calls is very high.


Provides good European languages. Acquired by Nuance.


Sphinx is open source and free. It works well if you have a trained acoustic model for your language and application. MRCP integration needs to be done for any real application.