Text-To-Speech Guide

© 2014 I6NET Solutions and Technologies, all rights reserved


The VXI* VoiceXML browser integrates an HTTP client interface to connect to an HTTP text-to-speech (TTS) server. This allows for dynamically generated audio content with a text-to-speech engine. Most VoiceXML browsers have an MRCP (Media Resource Control Protocol) interface to access text-to-speech features. The advantage however, of using the HTTP connector is that the “speech” generated is cached by the VoiceXML Browser, and re-used the next time. The text is posted via an HTTP request then the server responds with a standard wav file. Users can use the TTS to generate menus prompts, for example, without need to purchase a lot of TTS licenses. The integrated TTS packages use PHP, so you need to have an Apache/PHP already installed on your server (MySQL is optional, it allows to produce “CDR” like reporting information to evaluate the TTS using).



You can you two type of connections

  • HTTP access
  • MRCP access


To use TTS by HTTP, you need to configure vxi. In /etc/openvxi/client.cfg set POST value in client.prompt.resource.0.method key

client.prompt.resource.0.method             VXIString   POST


To use TTS by MCRP, you need to configure vxi, and configure asterisk to use TTS with MRCP.

To configure VXI, set in /etc/openvxi/client.cfg the ASTERISK in client.prompt.resource.0.method key

client.prompt.resource.0.method             VXIString   ASTERISK

To configure asterisk, update the file /etc/asterisk/mrcp.conf

version = 1
server-ip =
server-port = 554
resource-location = media
speechsynth = speechsynthesizer
speechrecog = speechrecognizer
rtp-ip =
;rtp-ip =
;rtp-ext-ip = auto
rtp-port-min = 5100
rtp-port-max = 5999
playout-delay = 50
;min-playout-delay = 20
max-playout-delay = 200
ptime = 20
codecs = PCMU PCMA L16/96/8000
rtcp = 1
rtcp-bye = 2
rtcp-tx-interval = 5000
rtcp-rx-resolution = 1000
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