IGEL Linux version 5.08.100 contains Nuance Citrix Client Audio Extension for Linux 7.47.0. The extension configures audio redirection on a Linux thin client in a Citrix environment, to provide optimal support for speech recognition.

Thin clients supported

Nuance supports the following IGEL thin clients with firmware version LX 5.08.100:

  • UDC2

Audio devices supported


Sound card ID

Sound card name


Philips SpeechMike III


SpeechMike III

Philips SpeechMike Premium


SpeechMike III

Grundig Digta SonicMic II


Digta Sonic Mic II

Grundig Digta SonicMic II (US edition)


Digta SonicMic II US

Grundig Digta SonicMic 3


Digta SonicMic 3

Button controls are not supported with the firmware available at the release of Capture Services (Desktop) 5.0

For the selection of audio devices, the following priority conditions apply:

  • If the environment variable NUANCE_USED_SOUNDCARDNUMBER has a valid sound card number, the corresponding audio device is used.
  • If one of the known sound card IDs is found in the system, the corresponding audio device is used. The sound card IDs are searched for in the order listed in the table above.
  • If no sound card ID is found, the default audio device is used.

Audio formats

The following audio formats are supported:

  • Nuance CELP 8 kHz 16-bit mono
  • Nuance CELP 16 kHz 16-bit mono
  • PCM 8 kHz, 16-bit mono
  • PCM 16 kHz, 16-bit mono
  • Speex


Installing on an IGEL thin client (firmware version 5.08.100 or higher):

In version 5.08.100 and higher, the Nuance Citrix Client Audio Extension is delivered with the IGEL firmware. To activate the extension, do the following:

  1. Start the IGEL Setup utility.
  2. In the Sessions tab, browse for: Citrix XenDesktop / XenApp > HDX / ICA Global > Mapping > Device Support
  3. Enable Nuance Channel for Dictation.


To enable logging, do the following:

  1. Make sure that log4crc is available in the $HOME directory of the user who starts the client and rename it to .log4crc. For example:
    cp /usr/lib/ICAClient/log4crc /userhome/.log4crc
    Open .log4crc; if the file is read-only change it to read/write (you must have permissions to change the file).
  2. Set the priority to trace (for detailed logging) or error (for error logging only) and change the line which begins with category name = to:
    Audio extension: nuance.smac.citrix.sbext
    Mixer: nuance.smac.citrix.mixer
    If you do not want logging, comment out these lines or remove the .log4crc file completely.


  • To change the destination of the logging directory the ICA client user must have write permissions to the directory and it must exist. The default output folder is: logdir="/tmp/"
  • The log file prefix is the first part of the file name. The default settings are:
    Audio extension: prefix="nca_ica_log"
    Mixer: prefix="nca_ica_mixer_log"

Audio extension names are nca_ica_log.n and mixer nca_ica_mixer_log.n (where n is a consecutive number).

  • Every log file has a number appended to its prefix name. Numbers begin at 0 and existing log files are renamed to next consecutive number; the newest log file always has the number 0.
    maxnum sets the maximum number of log files created. To have 5 log files, set the maxnum as follows: maxnum="5"
    Older files are deleted when there are more than 5 files.
  • maxsize sets the maximum size of a log file in bytes. If the maximum size is reached, the log file will be renamed to next number following the policy from maxnum and a new log file is created with the number 0. The default settings are:
    Audio extension: maxsize="20000000"
    Mixer: maxsize="5000000"

Philips SpeechMike

Button redirection: For Philips SpeechMike and Foot Control devices contact Philips Speech Processing Solutions. The Nuance Citrix Audio Extension does not provide support for SpeechMike button redirection.

SpeechMike (USB) audio: To use the Philips SpeechMike if it is not the default audio device, set the environment variable NUANCE_USED_SOUNDCARDNUMBER to the sound card number of the SpeechMike. If the environment variable does not exist or is invalid, the default sound card will be used.

Internal sound card

Recording with the internal sound card is not supported.

Using the internal sound card in parallel with a USB audio device is currently not possible because it is not possible to set the internal sound card as the default sound card when a USB default audio device is plugged in.