We’ll go through the process of installing and Configuring Festival Speech-to-text utility developed by University of Edinburgh, UK community.
Text-to-speech conversion is very crucial when working with Asterisk Pbx or any Media servers used for routing calls. Text-to-speech utilities are used to convert strings of words into audio that can be played to the callers using the system. Text-to-speech is not a replacement for professionally recorded prompts.

How to install Asterisk PBX 13.x on CentOS 7 step by step guide

Festival is free to use text-to-speech utility that works on all Linux systems. It is not recommended for production use because its sound quality is not clear enough, but used very often for development and testing purposes. For production use, you can have a look at Cepstral.

How to install Festival on CentOS and RHEL

sudo yum install festival

How to install Festival on Ubuntu

sudo apt-get install festival

Configuring Festival for use with Asterisk

After installing Festival, we would like to configure it to allow use with Asterisk PBX. To do this, we just have to edit festival.scm file located in /usr/share/festival/ directory. Open the file with any text editor you have.I will use vim:

vim /usr/share/festival/lib/festival.scm

Add the the following text just above the last line; (provide ‘festival):

(define (tts_textasterisk string mode)
(let ((wholeutt (utt.synth (eval (list 'Utterance 'Text string)))))
(utt.wave.resample wholeutt 8000)
(utt.wave.rescale wholeutt 5)
(utt.send.wave.client wholeutt)))

Save changes and restart the Festival server

sudo festival_server 2>&1 > /dev/null &

Go to your Asterisk source directory and verify that the app_festival application is selected under Aplications heading. If not, use make menuselect command to install Festival() diaplan apllication.If you had used my tutorial at

How to install Asterisk PBX 13.x on CentOS 7 step by step guide

as a reference for your installation, type

cd /usr/src/asterisk-13/asterisk-13.7.0/
make menuselect

Make sure it’s checked.See screen shot below

make install

Asterisk has to be configured to connect to Festival server on festival.conf file. There is a sample configuration file located in the Asterisk source directory.W e’ll copy it to /etc/asterisk/ directory then edit.

cd /usr/src/asterisk-13/asterisk-13.7.0/
cp configs/samples/festival.conf.sample /etc/asterisk/festival.conf

The default configuration is enough to connect to Festival server provided both are running on a local machine. If Festival service is running on a remote device, we’ll change the host parameter. All other configuration parameters will be left to default.

vim /etc/asterisk/festival.conf

Change where necessary.
To verify that Festival() dialplan application is running, type following command on Asterisk command line interface.

core show application festival

If you don’t get any output, first load the app_festival.so module:

module load app_festival.so 
module show app_festival.so

You can check file availability in /usr/lib/asterisk/modules.If you used my tutorial to install Asterisk, you may have realized that I compiled asterisk with libdir being –libdir=/usr/lib64. For this case, the module will be on

ls -lh /usr/lib64/asterisk/modules/app_festival.so

else:

ls -lh /usr/lib/asterisk/modules/app_festival.so

From here. you can create simple dialplan like one below for testing:

exten => 110,1,Verbose(2,Performing Festival test)
same => n,Answer()
same => n,System(echo "We are now doing Festival Test after successful installation" | /usr/bin/text2wave -scale 1.5 -F 8000 -o /tmp/test.wav)
same => n,Playback(/tmp/test)
same => n,System(rm -f /tmp/test.wav)
same => n,Hangup()

If you dial extension number 110, it should automatically record test.wav audio file from the string “We are now doing Festival Test after successful installation” and play it back to you.
Hope this tutorial helped someone.
You may also check on the following related tutorials:

How to Integrate Openfire XMPP Chat Server with Asterisk PBX server

Configuring Mapping between Openfire XMPP users and Asterisk SIP users

How to Install Latest Kamailio SIP Server on CentOS 7

Complete guide on how to Install Openfire XMPP chat server on Centos 7