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Voice Recognition


To use the London Control voice recognition function, the Microsoft voice recognition software must be installed on your computer (SAPI version 5.1 or 5.3). If you are running Windows XP, go to: http://www.microsoft.com/downloads/details.aspx?
and download the Speech SDK 5.1 (68MB approx), which also includes several tools to help with speech training etc.

To check whether you already have the voice recognition software installed on your computer, open the Control Panel. If you have a Speech icon double click on it. If this includes a Voice Recognition tab that includes an English Recogniser (v5.1 or later), then you have the correct software installed.

An English Recognizer must be installed to use the London Control voice recognition function. (Note that Windows Vista and Windows 7 Home and Business editions do not normally include an English Recognizer in non-English speaking countries. However, it is possible to install and run London Control and SAPI 5.1 on Vista and Win7 using the Microsoft Windows XP Mode. See our support page for more information.)

Using Voice Recognition in London Control

The London Control voice recognition function will recognise clearances and instructions spoken using proper R/T phraseology. The set of phrases that it will recognise consists of the most commonly used ATC instructions, and it is possible to combine many of these together to give multiple instructions to the same aircraft. The phraseology that can be recognised is defined in a Grammar Reference document that can be downloaded by clicking here.

There are a few things to note when using voice recognition:

  • The voice recognition only registers instructions when you press the Press To Talk switch (control keys and middle mouse button). Don't forget to release it as well. Also, don't forget to have your Mic set up as the source for sound input using your volume control (mixer).
  • The Microsoft voice recognition software takes control of the microphone and interferes with the London Control sidetone function. You will probably find that you need to set the sidetone volume to zero (use <Alt> <S> <R> to open the radio control window for this).
  • You will probably find that the voice recognition works better after some training (if you haven't trained it already).
  • You may want to set the Speech "Accuracy vs Response Time" setting a bit higher. It slows things down a bit, but gives better results. Go to Control Panel -> Speech -> Settings to do this.
  • If you have a stubborn aircraft that won't reply, try saying just the part of the callsign after the airline code (eg say "four six x-ray charlie climb flight level 320" for BAW46XC).
  • There are some new features included that are only accessible by voice command, like "squawk ident" and "report your heading".

Other FIRs

If you wish to use voice recognition in the Amsterdam or Scottish FIRs, you will need to download the appropriate grammar files. Click here to download the files. You will need to open the zip file and save the atc.cfg files to the appropriate folders in your London Control installation.

Voice Test Program

We have developed a little test program to allow you to see what London Control will recognise when you use it. This can be useful for testing the speech recognition after you have trained it. This program doesn't run London Control or do anything with the speech commands except display them on screen.

You can download the Voice Test Program here. The program downloads as a Zip file. Save this file to your hard drive, open it and run the program "LCVoiceTest.exe".

The Voice Test Program simply shows a list of the clearances and instructions that it recognises as you speak. There is no need to use the Press To Talk switch. There is also an audio level meter to assist in determing whether your microphone is set-up correctly.

Please note that the Voice Test Program displays the recognised speech as it will be processed by London Control. This means that the words you see will not necessarily match the exact phrase that was spoken. For example, extraneous words may be omitted and callsigns may be slightly garbled. This doesn't necessarily matter as London Control itself carries out further processing on the speech to determine more precisely what was said.

Voice Training

The speech recognition greatly improves if you train it. You can follow the standard Microsoft training sessions, from the Speech Control Panel, and these help a lot. One of our customers has also prepared some voice training files that are specific to London Control and include the main words and phrases used to issue clearances and instructions to aircraft. They can be downloaded (in a zip file) by clicking here.

There is a ReadMe file included that gives instructions on how to use the training files, and our own Voice Test Program is also included. (Please note that you can only use the Voice Test Program if you have already bought and installed London Control.)


When I try to run London Control Iget an "OLE error 8004503A".
The Microsoft voice recognition software isn't installed. Look under the Requirements heading above for information on how to do this.

London Control pauses for a long time when I press the PTT switch.
Make sure the Microsoft voice recognition software is installed. If it is, uninstall and reinstall it.

Aircraft never respond when I give a voice command.
Check that your microphone is set up properly. Run the microphone configuration tool in the Speech control panel. Try training the voice recognition software. Depending on the performance of your computer, it may take a few seconds for aircraft to respond to your voice commands.

LCVoice works for the London FIR, but not for Amsterdam or Scottish.
Check that the file atc.cfg is installed in the Amsterdam and Scottish FIR directories. If not, download the grammar files and copy them to the appropriate FIR directories.

When running London Control on Windows Vista I get an error telling me to check my audio settings.
Make sure that you have an English Recognizer installed and selected in your speech recognition control panel and that you have your microphone plugged in and set up.


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